Drilling Down into the Code: Part 3

The Code for Sustainable Homes is a hotch potch. Whilst zero carbon and, to a much lesser extent, water use reduction have been discussed at length, if you were to build the most energy and water efficient house possible, you’d still only score 44% of the maximum available eco points. That would get you to Code Level 1. Code Level 6, the top level, requires a score of 90%.

So how would you go about garnering the other percentage points required to lever your house up from Code Level 1 to Level 6?

The answer is that you have to accumulate credits (of varying value) by undertaking all manner of other actions. Some are relatively easy:
• Provision for cycle storage — score 2.5%
• Provision of a home office — score 1.25%
• Provision of recycling bins and a compost bin — 4.75%
• Use EU approved insulation — 0.6%

Others are more taxing and potentially a lot more costly
• Build to Lifetime Homes standards — 4.75%
• Build to Secured by Design standards — 2.25%
• Improve on Part E sound regulations — 4.75%
• Use A+ rated materials from the Green Guide for Specification — 4.5%
• Build into the basement or the loftspace — 2.65%

You can only afford to lose 10% of the credits available if you want to qualify for Code Level 6. As there are likely to be some areas where your site cannot score at all, the likelihood is that designers will be forced to incorporate practically every feature mentioned in the Code. The elbow room for trade-off is remarkably limited.

This is where the Code gets into sticky ground. A lot of these features — there are 34 tests applied in all — are concerned with good design and best practice, but not necessarily to do with sustainability. For instance, having your builder signed up for the Considerate Contractors Scheme (worth 2.25%) is all very well but doesn’t really make much difference to climate change. So why is it being included in the Code?

And the requirement for A or A+ rated materials is effectively going to blacklist an awful lot of C rated materials. I am not sure the PVCu manufacturers have yet twigged this, but the Code has it in for them.

New urban design in practice

I made my second visit to Upton this week. For those of you not in the know, Upton is the new Poundbury. Sort of. It’s an urban extension (fancy modern term for a housing estate), tacked onto the edge of Northampton, and it’s full of weird and wonderful homes. I was there as part of a Princes Foundation seminar group and the guiding hand of this group is evidenced all over the development, though its much more diverse than Poundbury. Although at first glance it looks all very traditional, there are modernist schemes here as well and Bill Dunster’s Zed factory is hard at work on one corner delivering what they claim to be the first Code for Sustainable Homes Level 6 homes onto the market.

Only the southern side of the development is complete, the rest is still very much a building site. However, enough is there to give an impression of what it will be like when all 1200 homes are all done and dusted. In many ways, it’s the complete antithesis of selfbuild. Like Poundbury, the whole scheme is about urban design and master planning, building model settlements where everything is thought through and everything hopefully functions smoothly. It’s just as much about social engineering as it is architecture and consequently it all has a rather prissy, manicured feel to it.

But behind the glossy veneer of this exemplar development, most of the work is being undertaken by warts–n-all housebuilders and developers, and it’s not an easy site for them. Kim Slowe, of Cornhill Estates, one of the Upton developers, who cut his teeth at Poundbury, gave a very interesting presentation to the group and was quite upfront about the problems encountered. “Whereas homes in Poundbury sell for between £230 and £260 per square foot, up here in Upton we are lucky to get £165. It’s a very different social mix and quality building is a much harder sell. It’s challenging.”

And whereas the scheme density, the parking restrictions and the pepperpotting of social housing throughout the site doesn’t appear to cause any problems in Poundbury, these issues have all become thorns for the developers trying to woo in private buyers at Upton. By way of example, Slowe indicated that theft of building materials was an ongoing issue on this site. “It’s all very well using lead-lined canopies over the front doors, but the lead keeps getting stripped off.” Just around the corner from Slowe’s houses, I walked straight into the evidence that this was indeed the case – see image.

The verdict on the success or otherwise of Upton will be some time in coming, but you have to admire the vision and drive which enabled it all to get out of the ground. Do take a detour to go and visit the scheme and make your own mind up.


BTW, it’s not very well signposted. It’s on the western fringe of Northampton, next to the Sixfields football ground, the home of Northampton Town FC. Set your sat nav for NN5 4EZ and it should take you to Upton Square, the pulsing heart of the place, right next to the brand new primary school.

Offsite 2007

Four and a half hours scampering around the BRE car park in Watford today brought on a familiar feeling of having been here before. New housing exhibitions opening, like Offsite 2007, are always accompanied by a feeling of excitement, anticipation, even euphoria, but I come away a little let down and rather bemused. “What was all that about?” I ask myself. It was rather like Offsite 2005 – hardly surprising because it was largely the same people on the same site. But it also reminded me of the Milton Keynes Energy World exhibition in 1986. Twenty years on, what has really changed? On the one hand, you want to congratulate everyone for the phenomenal amount of work undertaken to get everything up and running for the opening event. On the other, you can’t help wondering who this is intended to impress, especially as I understand the public don’t get access to the BRE site.

The star of the show was the Kingspan Lighthouse, the first house in the country to achieve Level 6 of the Code for Sustainable Homes – i.e. it’s zero carbon. It was a peculiar looking affair with lots of chestnut siding wrapped around a tall thin three-storey structure. It didn’t really look like a house, but I think that was the point. In fact, none of the new exhibits looked like houses that we would instantly recognise as houses. Tear up the old, bring in the new. You get the message: this is about re-engineering our lives just as much as re-engineering our homes.

The guys in Stewart Milne’s Sigma showhouse seemed just a little miffed. Their house only got to Level 5 and that thanks to three roof-mounted wind turbines which, of course, weren’t even spinning, let alone producing any electricity. “We’d get a six if we built them in a courtyard setting,” explained their minder. It’s all got very competitive, very quickly.

The Hanson Eco-Oast House made the nicest space, making use of one large room upstairs room, lit and ventilated by the huge vaulted roof. It was the only one with any wow factor, the sort of thing to excite the middle classes. Everyone had balconies, lots of balconies and there was timber in every shade and species you could think of.

So well done everyone who has chipped into this event. But is this the roadmap for tomorrow’s housing? We’ll have to wait and see.

On Dynamic Insulation

Ever heard of dynamic insulation? It’s an idea that’s been knocking around for a long time, always in the category of academic curiosity, but now at long last someone is coming forward with a marketable product called Energyflo which, they hope, will bring the concept to the masses and, just possibly, sell in great quantities.

So what is it and how does it differ from ordinary insulation? In conventional building models, heat leaks out gradually through the fabric, be it a wall or a roof. Dynamic insulation seeks to capture that leaking heat and feed it back into the building. It does this by making the insulation layer air permeable (by punching loads of holes in it) and then de-pressurising the house so that air is drawn into the house, heating up as it passes through the walls or roof. In theory, if you get it right, you can recapture all the leaking heat and you could produce a wall with a U value of near zero, without having to use more than about 90mm of insulation.

To get it to work, you have to get a fan sucking like hell inside the building to pull the air inside. What happens to the air being sucked through the fan? Well, here it starts to unravel a little because it gets dumped outside. But in fairness, warm air is going to get dumped outside in any event because you need to have some form of ventilation built into the house and you may just be able to get a second bite at that dissipating heat if you plug in a heat recovery unit.

Last Wednesday (May 30), I sat in on a presentation given by Mohammed Imbabi and Andrew Peacock of Environmental Building Partnership, a spin out from Aberdeen University, which is planning to market Energyflo as the basis of a low energy building solution. They reckon that with no airflow at all, the U value of the 95mm expanded polystyrene panels would be around 0.35, but with the airflow working as planned, the U value falls to around zero: i.e. there will be no heat loss at all.

Of course, it’s early days for this product. It’s still undergoing tests, most notably at a CALA homes site in Edinburgh where it’s been installed in the roofspace. There are also plans for it to be used on a big apartment site in Dubai.

I don’t think the presentation met with quite the level of appreciation the backers were hoping for. Many of the questions expressed a surprising level of scepticism. To work as designed, the Energyflo cells have an air filter embedded within them: someone suggested that this would rapidly clog up in Dubai where there are frequent dust storms. And there appeared to be a finite life to the cells as well, which was determined by the site characteristics (i.e. how much pollution) and the thickness of the filter. But if you are building the insulation into the fabric of the structure, how are you meant to replace it?

Perhaps its churlish to be too critical. As a product, it’s only just making it’s first tentative steps away from the research labs and there is doubtless much to be learned en route. To establish a foothold in the insulation market, it will have to be monitored on a number of different buildings over a lengthy time period, something we in the UK are not good at doing. So I wish them well, but don’t expect to be seeing a whole mass of dynamically insulated buildings tomorrow or in fact anytime soon.

Dunstervision Part 2

Yesterday, I went to Think07, a new conference/exhibition put on at London’s Excel by CMP Information, owners of Building magazine and Property Week. With my press pass whisking me hither and thither, I spent a really enjoyable six hours there talking to a variety of people and listening to talks from a number of distinguished speakers including green skyscraper-builder Ken Yeang, Sainsbury’s boss Justin King (very slick performer, a politician-in-the-making) and BedZed’s Bill Dunster. Having featured Dunster in this blog very recently (Apr 3rd) and been somewhat critical of his obsession with wind turbines and PV cells, I thought it would be a good opportunity to see what he has to say about the matter.

To his credit, he doesn’t shrink this issue. “Let’s throw away this offsetting concept,” he said. “The job we have ahead of us is to get the world ready to run on renewable energy because fossil fuels are running out.” So far so good, I am right with him. However, he then launches into some very contentious stuff which he admitted got him into long arguments with engineering buffs. Firstly he insists that renewable energy will only ever be capable of supplying 30% of our current electricity use and, furthermore, that a green grid would only be able to supply about half of this 30% and that, consequently, the rest had to come from on site renewables.

I quizzed him about this in the Q&A session at the end, chaired by Zero Champion’s Phil Clark. “Bill,” I said, somewhat over familiarly perhaps, but what the heck, this was my moment in the limelight, “generating renewable power using mega wind turbines is much more efficient than on site. Isn’t it a mistake to mess around with microgeneration and shouldn’t we be concentrating on greening the grid instead?” Bill wouldn’t be moved. “It’s not either or, it’s both,” he said. “There simply isn’t the capacity to be able to produce that much renewable power from the grid.” It’s not exactly easy to have a conversation when you are in a room with about 100 other people listening in, but I managed a counterblast. “The North Sea is very big, you can get an awful lot of wind turbines out there.” Bill was unmoved. “It’s not nearly big enough. You are restricted to the Continental Shelf and you have to leave a large gap between each turbine and there simply isn’t enough space out there to generate all the electricity we need.” And that was the sum of our discourse.

Bill Dunster has done his homework. I can’t fault him for that. But has he got it correct? I had no idea. This morning I got out that swot’s handbook, Wikipedia, and started to look for an answer.

As you’d expect, there isn’t exactly a simple answer to such a question, but there are lots of pointers to suggest that I am right and Bill Dunster is wrong. Denmark, the country that pioneered wind turbines, already draws 20% of its electricity from wind and plans to make that 50% over the coming years. OK, it’s a small country, but it’s hard to imagine that the UK couldn’t do the same. There is another telling sentence in the article on renewable energy, although of course being Wikipedia there is no way of verifying it. Globally, the long-term technical potential of wind energy is believed to be five times current production global energy consumption or 40 times current electricity demand.

George Monbiot looks at this problem too in his book Heat where he has a chapter called How much energy can renewables supply? He mentions a 2005 government White Paper paper called
Offshore Renewables — The Potential Resource which confirms the figures coming out of Wikipedia — i.e. that our potential offshore wind generation capacity is enormous, over eight times our total current electricity demand. Obviously, there is a big gulf between what is potential and what will ever be practical but exactly what the limits to practicability are remains a matter of conjecture. What is clear is that assumptions are constantly changing and that off shore wind turbines seem to be getting bigger, and are getting placed further from shore and at ever deeper locations which suggest that the Danish expectation of delivering 50% of its electricity requirements from wind may not be far fetched at all. There is obviously a problem with the fact that wind is intermittent and that therefore wind on its own may never be able to supply all the electricity requirements. But then there are other technologies that may step up to the plate and fill the gap.

In truth, I haven’t spent as much time as I should researching this fascinating subject, but you can see that you don’t have to delve very deeply into it to see that Dunster’s contention that we will only ever be able to supply a small fraction of our electricity needs from large scale renewables looks pretty silly, as Denmark has already shown. So no, Bill, I am yet to be convinced that every home needs to be covered in PV cells and have a micro wind turbine attached to it.

There was another aspect of Dunster’s 40-minute lecture which raised the hackles of someone else in the audience. It was his contention that ground source heat pumps are bad news: “There is no heat pump anyone has yet designed that doesn’t double the electricity load.” As heat pumps are a form of electric heating, this is hardly surprising, but a heat pump can reduce the overall carbon emissions from a house because of their gearing effect — they manage to shift three or four units of heat energy from the ground outside into the house for every one unit of electricity used to run them. So to dismiss them out of hand because they use electricity does seem a tad eccentric.

Bill Dunster’s goal is, it seems, to always aim for zero-carbon on a site-by-site basis so the fact that heat pumps get you only part of the way there becomes a big drawback for him. Instead, he seems to prefer burning biomass. He mentioned something I hadn’t come across before, a National Biomass Quota, which suggests that each individual in the UK can burn up to 250kg of dry biomass per annum without causing undue stress on our resources. I think this is a concept born out of his own research and I have no idea how you would check it (Wikipedia doesn’t seem to have heard of it), but I can at least see where he is coming from. The problem for many biomass schemes is that whilst they can be seen to work fine for a handful of small developments, they don’t really represent a mass-market solution because of a shortage of biomass to burn. Whether this is so or not, who knows, but I guess that a Biomass Quota is an attempt to quantify just how much there is out there.

But the net upshot of all this is that Bill Dunster comes with lots of opinions and lots of baggage. He therefore causes debate and controversy. Put simply, not every agrees he’s got it right. His Zed Standard, which he touts as the best solution for zero energy living, is even more prescriptive than the German Passivhaus standard which I have been mildly critical of over recent months for itself being too prescriptive. At one point in his presentation, he asked, almost poignantly, “Why does the industry have such a negative view of BedZed?” This was very revealing because, by and large, I don’t think the industry does have a bad opinion of Bedzed. Far from it. Rather they maybe don’t have quite such a high opinion of it as Bill himself does. They give it 8 out of 10, not 10. I think he could more usefully ask: “Why doesn’t everyone agree with me?”

Passive Passive Houses

Spent the day in Nottingham at the School of the Built Environment, talking with its head, Prof Brian Ford, and two of his colleagues, Rosa Schiano-Phan and Mark Gillott. They had contacted me about my PassivHaus musings: it seems I am not the only one who has had a few doubts about whether this standard is all that it is cracked up to be.

In particular, they wanted to talk about low energy performance standards in warm (i.e. Mediterranean) climates. They have been part of a group of institutions, funded by the EU, which have been looking into creating a sort of PassivHaus-lite standard which would be better suited to Spain and Italy and, just possibly, to the UK and Ireland as well. Nottingham has a particular interest in natural ventilation techniques and they are worried that the German PassivHaus standard shuts out all but mechanical ventilation with heat recovery (MVHR) solutions. I share their disquiet. There remain a number of doubts as to whether MVHR is the best solution for all housing. What doubts?

• It’s mechanical: it requires a fan to operate: it therefore uses power.
• As it’s mechanical, it will require servicing. This may or may not get done. And it will of course break down from time to time.
• This raises one or two health issues. As PassivHaus is nearly airtight, indoor air quality is dependent on fans. What happens if the fans stop? Will anyone notice? Could it even be dangerous?
• People have raised concerns over the health implications of drawing input air through long lengths of ducting. In an ideal world, the ducting should be demountable for cleaning purposes but such a requirement doesn’t form part of the PassivHaus standard and seems likely to be ignored.
• In short, there is concern that the PassivHaus standard has got the balance wrong between carbon reduction and personal health.

But the Nottingham crew have further misgivings. They reckon the maximum space heating requirement figure, the famous 15kWh/m2/annum (the very nub of the PassivHaus standard), was actually too generous for warm climates. It seems to have been set with Germany or southern Sweden in mind: in the Mediterranean you simply don’t need that much heating, or to put it another way, you don’t have to build to PassivHaus standards to get such a predicted annual heat load. In fact, the cooling load is far more significant in the Mediterranean climate and they think it’s a much better approach to incorporate natural ventilation techniques, which can keep the air fresh in winter and cool in summer.

How does this relate to the UK? Here we are in mid-April with the daily maximum temperatures well into the 20s, and having just experienced nothing more than a one-week winter. It’s hard not to conclude that the climate we are experiencing has already changed significantly. The question is why are we getting obsessed with a performance standard (i.e.PassivHaus) which is a) not entirely applicable to our climate and b) over-prescriptive about U values, air tightness and ventilation techniques? They are worried that the PassivHaus standard will somehow morph its way into our SAP ratings as the only way to build a zero-carbon house and that other more compelling options will be effectively shut out.

To this end, the Nottingham group are working up an alternative low energy standard, a naturally ventilated version of PassivHaus (maybe that’s a Passive Passive House), which they think is better suited to warm climates and, just possibly, to the UK as well. They are planning a launch event and a very active debate about the pros and cons of PassivHaus in September (18th and 19th).

The other really interesting thing they are up to is building a series of experimental houses on the campus, to be known as the Creative Energy Homes. They already have one experimental house built on site seven years ago; now they will be erecting another six. There will be public access for some time and it’s sure to be a big draw. Pictured here is the Stoneguard C60 steel framed house, as it looked this afternoon in the balmy sunshine.

Dunstervision

This week’s Sunday Times has an article about Bill Dunster, rightly described as one of Britain’s foremost green architects and pictured here at his home with wife Sue. He’s still best known as the designer of
BedZed, the south London housing scheme that sits at the top of every magazine and newspaper’s stock photo library and gets aired every time they want to illustrate a feature on low energy housing. His more recent work expands upon the reputation he established there and he’s sort of trademarked the Zed-bit so that anything with a Zed in it, like ZEDHomes or ZEDFactory, is likely to have Dunster’s imprint on it. It’s easy to overlook the fact that ZED, in this instance, stands for Zero Energy Development, a critical feature of all his designs.

But Dunster’s not without his foibles. One of the things he’s really into is thermal mass, which requires the use of tonnes and tonnes of concrete to act as a heat store for his houses. This is done to facilitate passive solar design, already discussed on the blog (see Feb 21st 2007 entry). But using masses of readymix concrete upsets a lot of greens because, well, it’s concrete. And it also upsets the MMC set, because you can’t sensibly prefabricate it in a factory.

He also manages to upset the PassivHaus crowd by rejecting mechanical ventilation with heat recovery and instead espousing wind-assisted passive stack ventilation. This is indeed the raison d’etre behind the massive multi-coloured cowls that sit on top of BedZed, which make the place both other-worldly and photogenic. As you can see, Bill Dunster is not everyone’s cup of green tea.

Personally, I don’t have a problem with using lots of concrete or not using any fans. He puts forward credible arguments for both viewpoints and is all for recapturing the carbon used to make the concrete over the lifetime of the buildings.

But there is one aspect of Dunster’s vision that does trouble me. That is his predilection for site-generated renewable power. In the quest to create zero carbon developments, Dunster seems to have gone overboard on installing renewable technologies, and wind turbines in particular, that really don’t make much sense. And the Sunday Times feature has an interesting clue as to why that might be. In discussing Bill and Sue Dunster’s own house in East Molesey, Surrey, it states “Last year, the Dunsters took great pleasure in disconnecting from mains gas.”

Just why should this fact be a cause for celebration chez Dunster? I am going out on a limb here and speculating that it all stems from a peculiarly British strand of green building, which seeks autonomous or self-sufficient development as an end in itself. There were the John Seymour books published in the 1970s which put forward self sufficiency as a desirable goal, and there were also Brenda & Robert Vales’s books, the Self Sufficient House and the Autonomous House. These plotted a vision where each house was a little island which produced its own food, generated its own energy and disposed of its own waste. These self-sufficient stirrings were being mirrored on the TV at the same time by the antics of Tom and Barbara in The Good Life, a sitcom set in Surbiton — very close as it would happen to East Molesey, home of Bill and Sue.

But I didn’t get self-sufficiency back in the 1970s and I still don’t get it. What is the point? We are social creatures, born to trade and barter, and we get ahead by specialising, by getting a skill set that others don’t have and by making ourselves useful to a wide number of people. Aiming to be self-sufficient seems to be running counter to all this: you need to be part gardener, part engineer, part builder and part composter. In fact, you need to be full time peasant. It may well suit some people but methinks not that many. Most people would prefer to live by their wits and get specialists to look after these aspects of their lives, which is why supermarkets, builders and utility companies always do good business, whatever the economic outlook.

Following on from this, the trends towards decentralised power and, in particular, on-site renewables seems to be driven in good part by a Tom & Barbara agenda. We have a country criss-crossed with energy supply lines, and we have professional power supply companies queuing up to deliver renewably generated electricity into the grid, planning problems not withstanding. Yet at the same time we are being encouraged to bake our own electricity on site, as if this in itself was a worthy goal, and despite the fact that common sense says it would be much more efficiently generated off site. There is now a healthy ongoing debate about just what exactly the definition of on site should be, at least from a power generation standpoint. Could it include a neighbourhood wind turbine? Or a combined heat and power plant for an estate? Or, heaven forbid, just buying green electricity from the grid. You might think it’s all a bit academic, but it’s a point that has become central to the definition of what a zero-carbon home may or may not be. And it’s become central to the work of Bill Dunster, because without on site renewables he can’t build a ZEDHome.

But does it really make sense as a model by which to power the carbon-lite economy? Or are on-site renewables just a throwback to 1970s woolly thinking?

Low energy housing in Sweden, Denmark & Germany

On Friday, I attended the debriefing session run by the DTI Global Watch Mission, which sent a small party to Sweden, Denmark and Germany in November. It was similar, in many ways, to the PassivHaus study tour, which I went on in February, but it was a longer tour looking at a wider range of low energy housing projects.

The general consensus was also pretty similar to that drawn by the PassivHaus study tour. In all three countries, they were looking at the same sort of things: a small number of exemplar projects, all with the emphasis is on pretty much the same features: massive insulation levels, air tightness, triple glazing, mechanical ventilation with heat recovery and a little booster heating to get things up to par. It’s a recurring theme: you’d be tempted to think that maybe they have the solution to the conundrum of how best to construct low energy housing.

However, there are subtle differences between the three national approaches. In no particular order, here are some of the notes and calculations I made, as a result of attending the session.

• 80% of new homes in Sweden are heated with electric heat pumps, of which over 60% are ground source heat pumps. Remember, Sweden has loads of hydro-electricity, so electric heating makes sense for them in ways it doesn’t in other territories. They use to prefer the cheaper air-to-air heat pumps but people found them noisy and the growth in the market is now happening with ground source heat pumps.

• In Denmark, 60% of homes have a supply of hot water pumped into the house from a district heating system.

• The Germans pay 50 cents (33p) per kWh for renewably generated electricity sold on to the grid. No other nation does this. Consequently, German roofs are covered in PV arrays.

• Micro Combined Heat and Power plant (CHP), fired by the Stirling engine, throw off one unit of electricity for every seven units of heat. You end up with far too much heat for optimal use. However, the next generation of fuel cell-based CHP, which should be commercially available by around 2010, should produce roughly equal amounts of heat and electricity. This should address the output issue, but at the moment fuel cell CHP is anything but micro: it requires a dedicated plant room.

• There is yet another low energy standard that was mentioned that I hadn’t come across before. The 3-litre house. This refers to the amount of heating oil required to provide space heating for each square meter of a house each year. 3-litres is reckoned to be the bees knees for renovations. 7-litre houses are something close to the building regs standard in Germany: in contrast, the PassivHaus standard is lower still, probably around 1.5-lts. This fascinating new take on a performance standard sent me scurrying off to my Excel spreadsheet which analyses our home usage. On this basis, I reckon ours is an 8-litre house! For a house built 15 years ago, that’s not too bad but I am not sure I should boast about it.

• The 2006 Part L building regulation for England & Wales indicates a space heating requirement or around 40kWh/m2/annum. I reckon that could be termed as a 4-litre house. Or maybe it’s nearer 5.

• Don’t say it too loudly, but we use another 4 litres per annum per m2 just to heat our domestic hot water. These extra litres are somehow overlooked from the standard.

• The Swedes, the Danes, the Germans and the Brits all seem to design homes with a 60-year lifespan. Quite where this 60-year figure came from, I have no idea. Why not 50? Or 75? How come everyone settled on 60?

• Having said that, only around 15,000 homes are demolished every year in the UK. That is one tiny number when compared to the 180,000 new ones built and the 25 million homes that currently exist. At that rate, it will take 1667 years before we manage to replace all the existing homes we have built, which is precisely 1607 years more than their design life. Does anyone foresee any problems building up here?

• The NHBC reckon that currently 47% of new homes being built in the UK are apartments. How long are they going to have to last?

PassivHaus v Passive Solar

I keep posting about Passive Houses and I must move on to something new. But before I get there, a query has come up that deserves a detailed response. What is the difference between a Passive House and a Passive Solar House? Are they the same thing? If not, how are they related? A bit of history is order here.

The Passive Solar House
Passive solar houses have been around a long time, arguably since we started putting windows in houses, whenever that was. It is a term used to describe a design principle that seeks to orientate a house so that the main living areas face the sun. The idea being that the sunshine heats the house, even on the most gloomy winter’s day, and that if the house contains enough heavy material, this free heat is stored overnight and slowly dissipates.

People got terribly excited about such concepts back in the 1970s and 80s. My very first building job, in 1980, involved doing a passive solar makeover of my house in Cambridge, carried out to the plans of Robert & Brenda Vale, who have since become the godparents of the UK’s green building movement. The house is still very much around (pictured here) and I revisited late last year: the current owner is aware of its history but is largely unimpressed by the thermal performance. “I don’t think my heating bills have been especially low, that’s for sure,” she told me, good-naturedly. She didn’t buy the house to save on heating costs: just as well.

Whereas it seems some climates, notably New Mexico and Arizona, seem to be ideally suited to passive solar designs, wet and cloudy Britain most definitely isn’t. That’s not to say that you can’t get any benefit from passive solar design, but it’s far more limited than its proponents make out. You have to build a high thermal mass house, which doesn’t suit everyone or every budget; you have to get the orientation right, which isn’t always possible; and you have to take extra measures to ensure you don’t suffer from summer overheating.

That’s not to say there isn’t still huge interest in passive solar as a design concept. Back in January, I was in the Building Centre Bookshop in London and there, on prominent display, was James Kachadorian’s The Passive Solar House. Kachadorian was custom homebuilder from Vermont who discovered passive solar design in the 1970s and built around 300 passive solar homes for his customers. He started designing in air ducts built into the floor, which he referred to as the Solar Slab and, despite lots of other people having very similar ideas at the time, he took out patents to try and protect his designs. When the patents ran out, he wrote the details up in this book, which he sees as a primer for passive solar designers.

However, his schemes started to unravel when there were outbreaks of mould inside his some of his air ducts and also when people started to realise that his houses certainly weren’t “homes without heating” which is how Kachadorian was (and continues) spinning it. “A beautiful, comfortable home that needs a backup furnace (boiler) or air conditioner only rarely” is how he puts it in the blurb of the book. But the text reveals a very different story: there is a still a significant heat load and a typical requirement is for a 12kW furnace, not small by current standards. Insulate the house better and you wouldn’t require nearly so much heat in the first place.

In fact, this is one of the problems with passive solar design. As you increase the amount of insulation in the fabric of the building, you decrease the heat load and you decrease the length of the heating season too. Instead of needing space heating on from say, September to April, a super-insulated house only requires it on from November to February. So your passive solar input just isn’t required so much and when you do need it, in the depths of winter, it’s delivering the least energy. The concept works best in the so-called shoulder seasons and, with a super-insulated house, you simply don’t need much extra heat at these times.

So the two principles, passive solar design and super insulation, are to some extent working against each other. In contrast to the Passive Solar Home, the German PassivHaus standard sits firmly in the super-insulation camp. Which begs another question. Why exactly did they call it PassivHaus?

PassivHaus
Whereas I think the original use of the term passive solar was to distinguish it from active solar, as used for specific applications like solar panels, the Germans seem to be using the term in a different sense which I can only liken to lying easy of the planet. Rather than actively consuming lots of the world’s resources, a PassivHaus will sit there in the background not doing any harm. Being passive, in fact.

Now a PassivHaus doesn’t need to be a passive solar house. It doesn’t need to be orientated towards the sun, nor does it requires tonnes and tonnes of thermal mass, though the great majority of German PassivHauses are masonry. These factors are taken into account on the modelling software used to determine the thermal performance of the design, and they will contribute to the overall performance, but they are not essential.

So in summary, passive solar house is a concept borne out of the first energy crisis in the 1970s and is all to do with using sunshine to heat the house. PassivHaus is a 90s concept, a rigorous performance standard emphasising the importance of super-insulation. As so often, Wikipedia is excellent on the differences in definition. Search on passive solar and passive house and you get two very different entries.

So what is a Passive House?

Passive House
The anglicised version of PassivHaus is not really defined at all. Hence the confusion. I have been using it interchangeably with PassivHaus, the German performance standard, but I guess there will be a lot of people around who are still far more familiar with the older concept of the Passive Solar House and will assume that this is what is being talked about. And I expect this confusion to persist for a while yet now that George Monbiot has latched onto the concept and seems to be writing about it frequently in his Guardian column. We can expect the phrase Passive House to get widespread media coverage in the months and years ahead.

But I wonder how many people will be aware of the nuances at work here. Or how many of them will just resort to the sloppy thinking which defines it as neither as a passive solar house nor a super-insulated house but simply as a House that doesn’t need a heating system. Which, as it turns out, is not the case for either meaning.

The Passive House: thoughts and reflections

There were a couple of moments when the PassivHaus study tour seemed to lose all contact with normality and enter into a surrealist daydream. Picture around 20 people, crammed into a cellar, with a few more hanging out in the passageway outside unable to get in for lack of space. We were listening, or trying to listen, to the architect, Carsten Grobe, who was explaining with the aid of a translator about the mechanical systems employed to heat the Passive House, which he had designed and built back in 1998 and in whose basement we were now standing.

One of our party asked what the carbon emissions were like for this house. Carsten gave a long and detailed explanation as to why the indoor air quality was very good and insisted that they had no problem at all with carbon emissions. It was an eloquent answer to a very different question.

You might think that this was just a translation problem and that he hadn’t understood the question. But similar misunderstandings happened throughout the tour. Whilst the Germans had no problem explaining how they have engineered these houses to reduce space-heating demand to an absolute minimum, they looked flummoxed when we started going on about carbon emissions or used the dreaded phrase “zero carbon.” I began to realise that these are concepts that the Germans actually felt uncomfortable about and it highlighted a surprising difference in emphasis between Germany’s PassivHaus builders and the UK’s “carbon busters.”

You see, it’s no accident that one of the key benchmarks for Passive Houses is a maximum allowance for space heating requirements for each house and it is expressed in kilowatt-hours per square metre per annum — 15 is the magic number they are looking for in this context. In contrast, the UK regs now work in terms of carbon dioxide emissions per square metre per annum. Whilst the two units are related, they are not the same, not by a long chalk.

The kilowatt-hour (kWh) has the benefit of being simple to understand. It’s the unit we buy our gas and electricity in, and the related kilowatt is the preferred unit of power for our boilers, fires and electrical equipment. Even light bulbs are routinely rated in watts. Most people are familiar and easy with the watt, the kilowatt and the kilowatt-hour.

Carbon dioxide emissions, in contrast, are much trickier. They vary a lot depending on the type of fuel being burned. A kWh of gas releases less than half the CO2 of a kWh of electricity. Every fuel has a conversion factor, related back to mains gas, and some fuels have several. So the fuel you choose to burn in your house has a critical effect on the CO2 emissions but no effect on the kWh you use. Consequently, Carsten Grobe saw no contradiction in using electricity exclusively to power his ventilation/warm air heating system and to heat his domestic hot water when the solar panels weren’t producing.

The three schemes we visited around Hanover were all different, designed to show the different aspects of PassivHaus living. Carsten Grobe’s selfbuild represented one strand, the upmarket detached family home: we also saw a block of flats in Hanover itself and a terraced house set out on the Expo site to the south of the city. The weather was wet — very wet in fact — but not particularly cold for February, around 7°C, and I was certainly a little surprised to find radiators on in both the detached house and the flat. In fact, I was surprised to even find radiators at all, though they were small and unobtrusive.

Most Passive Houses are built without radiators, except for towel radiators in bathrooms. They aim to maintain an even temperature throughout the structure and Carsten explained that the only reason they had a radiator in their house at all was for odd occasions when their elderly parents came to stay and they appreciated a bit of extra warmth.

But just because Passive Houses rarely use radiators, it doesn’t follow that Passive Houses are “Homes without Heating” as we sometimes think of them as being. The actual space heating arrangements vary from site to site but the overriding principle seems to be to
a) having insulated the fabric down to a very low U value and having designed out all thermal bridges
b) you then fit energy-efficient triple-glazing into the openings
c) and then ensure that the resulting structure is virtually airtight.
d) Now you build in a mechanical ventilation system to supply fresh air
e) and you use a heat exchanger to take every available bit of heat from the extracted air and add it to the incoming air.
f) You then pass this pre-heated air through something called a post heater (a term I had not come across before) which brings it up to a comfortable temperature.

How much work this post heater has to do depends on how warm you like your house. The one in the terraced Passive House was capable of delivering 1.5kW and could produce an air temperature of 50°C if required. I was frankly surprised at this: it seemed to me that this was essentially a warm air heating system.

The standard method of heating new homes in Germany is to use underfloor heating combined with a gas boiler. PassivHaus eschews this approach on the grounds that you don’t need a full heating system in a Passive House. But it seems to me to offer an alternative that is no cheaper to install and possibly burns more carbon because it relies on electricity to power the fans and the air heater. It would certainly be no cheaper to run because electricity is habitually three times the price of gas.

And yet Passive Houses sell themselves in part by saying that you can offset the extra costs of building to the higher standard by saving money on not having to install a full heating system. Hmm. I was beginning to have my doubts.

Carsten gave us another little trick used by PassivHaus designers. He said it was extremely difficult to get a really low theoretical heat demand from a detached two-storey structure as there is just too much external envelope in proportion to floor area. An easy way around this conundrum was to add a third storey, in his case a basement, and to include this in the heated envelope. The floor area goes up 50% whilst the space heating demand rises much less. As you are looking to meet a target expressed in kWh/m2/annum, the job of reaching PassivHaus standard becomes that much easier.

You could argue that this is daft and that the total energy load is actually increased in order to meet some notional standard. In fact, you’d be right but it’s a criticism that can be levied at most of the other energy rating schemes as well, certainly all the ones that work on a floor area basis.

Maybe, I am carping. I suppose I do carp rather a lot. But I know others were also uneasy. We had Julia Hailes, author of the Green Consumers Guide, with us in our party and she was flabbergasted to see that Carsten’s house was full of halogen and tungsten lights with not a CF bulb anywhere to be seen. There is in fact no particular requirement in the PassivHaus code to use energy efficient lighting or appliances: this seems bizarre. Julia also asked at one point just how you would incorporate a cat flap into a Passive House, a question that was met by complete bafflement from our hosts. Maybe the word cat flap was lost in translation, or maybe it was another case of different agendas.

The embodied energy question was raised several times by various delegates. Was the extra investment in, say, triple-glazing filled with krypton really worth it either financially or in terms of carbon emissions? Again, it seemed to be something that the Germans hadn’t addressed. They seemed to be solely interested in designing homes which required less than 15kWh/m2/annum for space heating: there didn’t seem to be any room for critical reflection about this.

The first day of the tour was spent in the hotel listening to various presentations. One of the most interesting presentations was delivered by John Willoughby, the energy consultant and sage, who gave a 20-minute slide show on the History of Low Energy Building in the UK. He ran through many projects starting with the Wallasey School (1961), the Wates House at CAT (1976 and still the best insulated building in Britain), various solar houses in the 1970s, the Pennyland and Linford projects in Milton Keynes in the 1980s, right through to Hockerton and Bedzed, both realised within the past few years. He also drew our attention to the increasing number of energy codes:
• Code for Sustainable Homes
• EST Good-Best-Advanced Standards
• Eco Homes
• Bill Dunster’s Zed Standard
• PassivHaus
• AECB Gold and Silver Standard

He suggested we were becoming good at standards but not very good at implementing them. He also referred to another energy sage, David Pickles, who I remember seeing give a talk once where he said that low energy living is 10% technology and 90% lifestyle. This little aphorism kept plopping into my head as we made our way around the three Passive House sites the following day. The German PassivHaus builders really didn’t seem to care about this aspect of energy efficiency at all: they just wanted to get their buildings up to PassivHaus standard and move onto the next one. PassivHaus seems to be very much an engineering concept, designed to provide comfortable space heating with the minimum energy possible. But that, unfortunately, is it.

So I came away feeling PassivHaus is a flawed standard. It’s very good on space heating demand (in advance of anything we have built in the UK, except for a tiny number of exemplar projects like Bedzed), but questionable on heat delivery systems, so-so on hot water heating and almost non-existent on lighting and electrical goods used within the home. What is more, there don’t appear to be any plans to update or improve the PassivHaus standard to take into account the rising concerns about carbon emissions. As such, I really don’t see PassivHaus translating wholesale across to the UK, but we can certainly learn a lot from what they have achieved to date.

The principle lesson perhaps being that, whilst it is all too easy for me to carp on about what is wrong with the PassivHaus standard, or why it is not quite the dog’s bollocks (try translating that!), they have built loads of them. And the more they build, the less theoretical it becomes and the more practical it appears. Whereas we may be full of good intentions, the Germans (and the Austrians, who seem to be even more enamoured of PassivHaus than the Germans) have now built around 6,000.

They are also very keen to promote the PassivHaus concept to the non-German speaking world. To this end, the next PassivHaus annual conference will for the first time be bi-lingual in German and English. So if you want to go and learn more about it, you need to head for Bregenz in Austria on April 13/14.

Images from the Passive House Study Tour

First stop on our tour was this owner-architect built passive house in Ottbergen. The house was built in 1999 and is on three floors, each just over 100m2.



Carsten Grobe, the owner-architect, gave us a guided tour and spoke at length about construction and the mechanicals which are used to provide heating.




John Letton, MD of Formworks UK, pictured here in the living room of the Ottbergen house. Behind him are the triple glazed window units complete with integrated blinds.



Our second stop was this block of flats in Hanover, designed by architect Christian Grubert who was on hand to show us around.




The flat we looked at had a surprisingly large radiator in the living room which was definetly hot. In fact this flat has radiators in all the rooms.



Our group seemed to spend an inordinate amount of time in basements and cellars, looking at various bits of plant. Here under the Hohe Strasse flats, the architect explains how the building is heated and ventilated. The main point of interest here was a pellet boiler.



Our last port of call was a series of terrace houses at Kronsberg, a new development to the south of Hanover on the EXPO site. These 32 terraced houses are all built to the PassivHaus standard and have been extensively monitored. Note that each flat has a turf roof. The two projecting poles through the roof are the inlet and outlet for the ventilation system.



The particular houses are hybrid timber frame and masonry. The gable walls and party walls are precast concrete: thewalls between are timber frame. Here is a cut away of the timber frame walls exhibiting 300mm of insulation.



These terraces have no basement, unusual for new housing in Germany. The plant room is consequently in the loft, pictured here. Here John Willoughby and Gavin Hodgson (BRE) inspect the loft with our guide. The whole site is fed by a CHP plant which supplies pumped hot water into all homes. This is one of the pipes in the LH wall. To the right of the hot water tank is a post heater, wrapped up in silver foil.

Are Passive Houses the answer?

Tomorrow I am off on a Passive House (PassivHaus) study tour. I take an evening flight to Hanover and join seventy others at the Loccumer Hof Hotel for a day of lectures on Monday followed by a full day’s itinerary visiting three PassivHaus sites. Sandwiched between this is a gala evening meal at Hanover City Hall for which they have thoughtfully emailed us the menu. It looks to consist of about half the annual produce of Lower Saxony and I don’t anticipate many of the guests will be clubbing into the small hours after that lot.

For those of you who know little or nothing about Passive Houses or, more specifically, the PassivHaus standard, I can’t do better than to suggest you mug up at the relevant Wikipedia page.

The Passive House concept is beginning to get wide coverage in the UK media. It’s seen as the most advanced example of low energy housing anywhere on the planet and over 6,000 have been completed to date, mostly in Germany and Austria. In the UK, the BRE have taken it under their wing and it is they who are organising this study tour. The question we will no doubt all be asking is: “Is this the future of low carbon housebuilding?”

Whilst there are lots of plus points, there are also serious doubts in my mind about whether the PassivHaus standard is the perfect solution. In particular, what irks me most is that it sells itself as a performance standard – it is quite specific about just how much energy can be consumed per square metre of floor area — but it also adds several other stipulations about what you can and can’t include in a passive house. For instance, you must have mechanical ventilation with heat recovery, whether you want it or not, and you must have windows with ultra-low U values. Why is it so prescriptive about these items? Are they saying you can’t meet the performance standard without these features? Or is there some other reason for including them?

They say that passive houses can be either masonry or timber frame? But German timber frame is very different to British timber frame: is our local version of timber frame suitable or does it need more thermal mass? What about using other build systems like SIPS or ICFs?

There are also lots of issues to discuss like costs and transferability to other nations? As discussed on the blog recently, the UK has the smallest homes in Europe. It’s harder to lose 300mm of wall insulation in a rabbit hutch. Does it make sense to do so? And does the standard restrict house design to the rectangular box? Or can it be adapted to the more varied UK styles?

Another issue is the requirement for triple glazing: is the extra expense, not to mention the embodied energy used in manufacture, ever justifiable in the British climate? In fact, I hope the whole house embodied energy argument gets aired. It’s hardly worth reducing the annual carbon emissions from 5 tonnes to 2 tonnes if it’s going to take an extra 60 tonnes of carbon to manufacture and build. Whether it does or doesn’t, I have no idea. But it’s the time and the place to speculate about these issues and I’ll be posting my answers when I get back mid week.

Zero carbon: just another stupid target

I have been arguing for a little while now that the zero carbon home is not a sensible policy goal. The twin aims of low-energy housing and renewable power generation are both worthy in themselves but it make little sense for developers to be forced into providing both on each and every site, which by current reckoning will be the case after 2016.

Many low energy houses will be built at locations unsuitable for renewable power plant and, conversely, there is absolutely no reason why renewables shouldn’t be employed in all manner of places which have very little to do with low-energy buildings. By asking for both elements to be incorporated into new housing schemes, the government is once again making a target which will end up distorting common sense and ultimately wasting energy and resources.

Nevertheless, I have been surprised just how quickly the deceit that is the zero carbon home has started to unravel. A report in last week’s Building magazine states that two independent reports, both commissioned by housebuilders, have concluded that the best way that housebuilders can meet the zero carbon target on their forthcoming developments will be to switch from selling to leasing the finished product.

What possible difference can this make to energy consumption? Absolutely none at all. But, by so doing, the developers can enter into contracts with the leaseholders to force them to purchase electricity from a renewable power supplier, and that way the developers can claim the houses are zero carbon. Apparently, EU energy rules insist that homeowners must be able to choose any power supplier on the market and the only way of ensuring that the householders don’t switch to non-renewable supplies is to remove the rights that go with property ownership.

Talk about the tail wagging the dog. This really is a ridiculous situation. But this is what happens when you have government by soundbite. Silly targets get set and then clever people find ways of meeting these targets, without the underlying problems being properly addressed.

Thermal mass: does it really save energy?

There is quite a significant body of opinion that holds that high thermal mass is one of the keys to low energy consumption. A house with high mass can absorb passive solar gain in winter and takes less energy to keep cool in summer. That is the theory. I think it’s questionable at best. Let’s examine the issues.

Firstly, what is meant by thermal mass? The mass bit refers to the heaviness or density of an object or a material. High mass building materials are concrete, brick, stone and tiles. In the low mass corner, we have not so much materials like timber and plasterboard, which are still relatively heavy, but the hollow, lightweight building systems such as timber or steel frame. Already, you can see that what we are lining up here is a re-run of the old timber frame versus brick and block argument.

The thermal bit refers to the capacity of a material to absorb heat. Broadly speaking, the heavier and denser an object or a material, the more heat is absorbs. A cubic metre of concrete can store around 80kWh of heat energy: in contrast, a cubic metre of air holds almost nothing. A whole house full of air, kept 20°C above external temperature, holds as little as 5kWh of heat energy. The structural fabric enclosing it holds anywhere between 50kWh — if it’s lightweight — up to 500kWh if it’s really heavyweight. Heavyweight doesn’t just mean masonry. Although all forms of masonry construction are heavier than framed techniques, concrete and dense blocks are much heavier than aerated concrete blocks, as made by Celcon and Thermalite.

Now, according to the theory of passive solar design, if you can capture lots of free solar energy (via large glazed walls or conservatories), you can store this heat inside the walls and floors of your heavyweight structure. Then during the night, instead of having to put the heating system on full whack, you can enjoy a free ride from the heat stored inside the structure.

But here is Problem No 1. You need lots of glazing to draw lots of heat during the day: at night time, this glazing will be leaking much of this stored heat back outside. In fact, even really good double glazed units leak six times more heat at night than walls or roofs. You can design this problem out by using insulated shutters, which cover the glazing during the night but, for many reasons, insulated shutters have never caught on and seem unlikely to do so. The fashion for large glazed areas doesn’t go with shutters or even heavy draped curtains. An awful lot of your passive solar gains will be given back through the glazing at night.


Problem No 2. In climates like the UK, you can’t get more than a proportion of your winter space heating from solar radiation. It’s often estimated to be in between 20% and 35% of the total space heating load. It’s difficult to increase this proportion because if you insulate the house massively, you reduce the overall heat load but, in so doing, you also reduce the useful contribution from solar gain. Why? Because a massively insulated house shortens the period for which you require space heating to the just the very coldest months of the year, precisely the time when passive solar has the least energy on offer.

Problem No 3 concerns winter holidays. If you were to go on holiday for a while and turn the heating off, then all the heat stored in your high mass building will leak away. This is something I have learned from bitter experience, having twice returned to a freezing cold house in the depths of winter to find that it takes 48 hours of continuous heating for it to become comfortable. And that’s in a house that has been built using heavy masonry materials only on the ground floor.

The phenomenon at work here is referred to as coolth. That is what happens when the surrounding surfaces are relatively cool and you yourself radiate a lot of your own body heat out towards them. This makes you feel colder than the air temperature suggests. As the surfaces warm up, you radiate less, which in turn makes you feel warmer.

In winter, coolth is bad news and takes a lot of energy to eliminate. But in summer, it’s a very different story. The physics at work in summer is no different to what happens in winter – you feel cooler than the air temperature because you are radiating large amounts of heat towards a cool surface. Because of this, the high massers contend that you need a lot less air conditioning in a high mass house. Not that we use a lot of air conditioning in the UK yet, but global warming is expected to change all that very soon. In the USA, the summer cooling demand is almost as large as that for winter heating so an ability to cope with this energy load is likely to become a significant part of our future fuel bills.

However, there is a snag here as well. Call it Problem No 4. During a prolonged hot spell, the structure eventually achieves equilibrium with the surrounding air temperature. Consequently, your body stops radiating heat away and the coolth effect vanishes. A massive structure will still tend to even out the difference between day and night time temperatures, this is true, but this means that whilst you will feel marginally cooler in the day time, you will feel just a little bit hotter during the night. Now whilst this is not a problem in offices and schools, it is with housing, an awful lot of which is empty during the day. Now, the high massers argue that air conditioning is less likely to be turned on in a heavy house because of the coolth effect, but methinks they are exaggerating the effect of the phenomenon. There is no coolth to be had in the middle of the night during a heatwave.

So, as regards low energy building strategies, I believe thermal mass is a classic case of the curate’s egg — i.e. it’s good in parts. It’s probably seen at its best in places which are occupied mostly during the daylight hours — schools, offices, workshops. It can be a useful technique to employ with buildings in constant use such as hospitals and rest homes and, indeed, some housing. But to get any benefit, these homes must be occupied throughout the year and throughout the day. Or, as we have learned to say, 24/7/365. If the occupation is going to be intermittent then there is every chance that high mass can end up being an energy drain.

Baufritz, the biological housebuilders

Last week I went on a rare expenses paid jolly to Germany. I was guest of Bavarian housebuilder Baufritz who, like many others in Germany, have watched Huf Haus blaze a trail into the UK selfbuild market and would like to do the same themselves.

There are something like a hundred fertighaus (factory house) companies in Germany, in the Huf Haus/Baufritz mould. They typically build a few hundred homes each year, similar in size to what several timber frame housebuilders do over here. The German businesses are also usually timber frame but it’s not timber frame as we know it in the UK. Here, we tend to supply just the timber skeleton, the superstructure, which then has to be finished on site. The Germans, by contrast, assemble most of the house, including internal and external wall finishes, in what is sometimes referred to as a closed-panel system.

To a visitor from the UK, the gleaming efficiency of the production lines is a site to behold. It’s reminiscent of car factories with wall and roof panels moving through assembly lines with a minimum of human intervention. If you want to read up more on it, there is a very funny description on the But She’s a Girl blogsite. Baufritz produce around 250 houses a year with a staff of 260, of which around 80 work in the factory and a further 60 work on site as erection crews. Work it out: it’s roughly one house per person per year. Say 1800 hours input. In the UK, you would expect to see between 3000 and 5000 hours work go into a traditionally-built house of similar size, and not that much less for a timber-frame one.

The reasons for this different approach are several.
• German’s pay high tax on overtime so there is an incentive to increase production from regular working hours.
• Germany hasn’t experienced the housing booms and busts that we have had in the UK. Consequently, German builders are confident enough to invest in manufacturing facilities.
• Unlike in the UK, Germans rarely seem to sell family companies and they tend to invest for the long term. Baufritz is a good example: it is owned and managed by the fourth generation of the Fritz family.
• The basic German house shape is simpler and less variable than its British equivalent. It lends itself to prefabrication.
• Planning permission for homes in rural districts is much easier to obtain in Germany and the selfbuild market is much larger, maybe ten times the size of the UK
• Without wishing to resort to oversimplistic stereotypes, Germans seem to be naturally good at organisation, teamwork and manufacturing. In contrast, Brits are more inventive, more willing to experiment and quicker to embrace change. All these factors combine to explain why prefabrication has taken off in Germany but struggled in the UK, for it’s expensive to change horses when you have invested huge amounts of money on one particular method.

And there are elements of German housebuilding that are surprisingly conservative. Various innovations which have been widely taken up in British housebuilding have seemingly been ignored in Germany. Trussed roofs, engineered timber beams, precast concrete flooring: no sign of these in Germany, as far as I can work out. In fact, most fertighaus builders lay a wet concrete screed within the intermediate floor, just because that’s the way it has always been done, despite the fact that it stops the house erection process stone dead whilst the concrete dries.

Consequently, German housebuilders tend to be looked at as being much of a muchness. Very, very good at what they do, but a rather limited range. Huf Haus stand out because they have gone down a most unusual design route and have decided to build these iconic black wood and glass houses, designer conservatories for the minamalistically inclined. But how does the competion differentiate itself?

Well, Baufritz specialise in what they call the biological approach to homebuilding, as promoted by the IBN (Institut fur Baubiologie) in Neubeuern. If I can summarize just what it is Baufritz’s take on a healthy house is, it seems to be:
• avoid all products from the petro-chemical industry
• use only untreated timber (and lots of it)
• insulate with compressed wood shavings treated with whey (for fireproofing) and soda (as an insect repellent)
• rely on natural ventilation– avoiding mechanical ventilation systems
• shield against electro-magnetic radiation
• use radiant heating systems — both underfloor and in-wall

Their take on mechanical ventilation is certainly unconventional and puts them at odds with the Passive Haus movement, who promote ultra low energy housing in Germany. Not that a Baufritz house is a high energy burner: on the contrary, they seem to be building some of the best insulated homes I have ever seen. The biological builders approach is simply to monitor indoor air quality via a carbon dioxide detector and then to open a window if things look to be a little struffy. They also don’t insist on extractor fans nor trickle vents, two of the banes of UK building regs. A Baufritz home doesn’t suffer from condensation - it’s simply too warm and well insulated.

The other really revealing technological aspect of their homebuilding is their using a specially-prepared plasterboard with a carbon skin which attracts and earths electro magnetic radiation. I have never seen nor heard of such a thing before. They take electrosmog very seriously and insist on getting radiation levels right down to trace levels, and have equipment on hand to prove it. Having written somewhat dismissively about the threat of electrosmog on this blog in June, I must admit that I am beginning to start getting worried about it!

The healthy house is a difficult call from a marketing point of view. Whilst no one would possibly object to living in a healthy house, there is just a slight fear that paying good money for levels of protection not available in normal housing is verging on being paranoid. People may worry about microwave ovens and mobile phones, but not enough to stop using them and so they may well feel that buying a biological home is a bit weird. I asked the heavily-pregnant owner/manager, Dagmar Fritz, pictured here, how many of their sales resulted specifically from customers demanding healthy homes and she admitted the number wasn’t that high. The reason they build biologically is because of a family commitment to the issue and Baufritz have established a unique reputation amongst German factory house builders and are now poised to see what the UK makes of their offerings.

It will be fascinating to find out. Oliver Rehm, a friend of Dagmar’s since student days, and a UK resident has gone into partnership with Baufritz to sell their houses into the British market. They have established an office in Cambridge are currently working through various technical approval issues. They don’t have any brochures or pattern books; everything is bespoke. Prices have yet to be finalised but expect a Baufritz house to cost something similar to a Huf Haus, that is to say around the £1500 per sq metre mark, making a four- bedroom, 2,000 sq m house £300,000. That puts it firmly at the upper end of the cost spectrum, and probably aims it at the prosperous South East corner of the country. Still, I can see them going well with people who admire the quality of German factory housebuilders and yet don’t want something quite as severe as Huf Haus.

Bill Dunster's walls

Bill Dunster is, for want of a better word, an ecotect. That is an architect with a passion for green design. He sprang to fame with a project known as BedZed, a development of live-work units built on a disused sewage farm in Beddington, South London. It’s had acres of publicity and is rightly held up as an exemplar of how multiple housing units should be built in the future. But BedZed has now been finished for three years and Dunster has found it a hard act to follow. Developers and social housing landlords have not been falling over each other to repeat “the experiment” and he has been frustrated by planners who haven’t been prepared to loosen the planning corset just because a scheme is green.

But at last, Dunster has another scheme to showcase his talent. This time it’s a four-storey block of key worker flats on the St Matthews council estate in Lambeth, South London. It’s not quite as big or prestigious as BedZed but in some ways it’s more technically advanced. Building carried a feature on it this week, which caught my eye: in particular, the wall detailing. The outer walls are no less than 550mm wide, compared with just under 300mm in conventional housing. They are made up of 150mm blockwork inside 300mm of expanded polystyrene insulation filling the cavity, behind a 100mm brick skin, which is what them outside world sees. The plus point is of course that, with this much insulation, you have got a tremendously low U value – reckoned to be just 0.1W/K/m2. But against this, on a 60m2 apartment, you are loosing up to 25% of the footprint to walling.

Yikes. That’s a hell of a lot, especially considering we are being encouraged to build smaller and smaller units. Dunster is a big fan of heavy mass construction, which means little or no timber frame and little or no off-site pre-fabrication. He believes in the importance of thermal mass (concrete in other words) in regulating the temperature characteristics of a home and in reducing the effects of summer over-heating. But is thermal mass really such a wonderful concept that you have to loose 20% or more of your floor area just to accommodate it? If there wasn’t quite so much south-facing glazing — another of his betes verts — then perhaps the designs wouldn’t require quite so much thermal mass and the walls wouldn't have to be quite so thick.

Another problem comes with the adoption of a 300mm cavity, shown here in diagramatic form, (ref Building magazine). How do you manage the openings? In particular, how do you ensure that the water penetrating the outer brickwork is directed back out of the external wall rather than dripping down into the joinery? You’ve left the world of conventional construction far behind here: there are no off-the-peg wall ties this long and there are no pre-formed cavity trays this wide. Dunster’s solution has been to design a wrap-around cavity tray around each window. To me, it sounds just like the sort of detail which is likely to fall victim to sloppiness on site. Done perfectly, there should never be any problem but construction isn’t a perfect world.

One other feature of this article stands out. The costings. £1600/m2. This isn’t, in fact, far out of line with many other innovative social housing projects being built around the country at the moment, but it’s about twice the rate that selfbuilders hope to complete their projects for. Why the huge discrepancy? A good question, which will have to wait for another blog.