How should we handle Humidity?

I still hear the old canard that 80% of our body weight is made up of water. I remember hearing it back at school and I’ve had it repeated to me by my children, so it feels like it’s still doing the rounds. Actually, that fount of all knowledge, Wikipedia, reckons it’s rather less, around 55% for men and 51% for women (more fat). I am not going to argue. It’s perhaps not 80% but it’s still a hell of a lot of water.

What you don’t so often hear — in fact just about never — is what proportion of your home is made up of water. I am not talking about water in the pipes and in the hot water cylinder and various tanks: I am referring to water bound up in the fabric of the house. There’s a surprising amount: nothing like the 50-odd% that exists in the human body but very possibly around 10% of the mass of a house will be made up of bound-water. Timber, for instance, has a moisture content which varies from as little as 5% (incredibly dry) up to over 30% (dripping wet), but often tends to settle down in a centrally heated house at around 10%. Masonry materials, even concrete, are hygroscopic to a surprising extent and can take on and release moisture according to conditions. You only have to drop a brick in a bucket of water to see the effect it has on its weight.

The fact is that a detached house, which can weigh anything between 50 and 200 tonnes, depending on size and construction methods (and that’s excluding all the foundations), could be holding as much as 10 tonnes of bound water within the walls, floors and roofing, and a lot more within the fixtures and fittings as well.

What does 10 tonnes of water look like? Due to the miracle of metricated measurements, 10 tonnes of water turns out to be 10m3 in volume, about the size of a small bedroom, or perhaps 70 bathfulls, if you prefer that. It also turns out to be 10,000litres, which is the amount of water a typical household uses in about two weeks, or around 1500 flushes on a 6lt low flush toilet.

All this bound-water doesn’t have to stay bound. When conditions dictate otherwise, it can either absorb more water or it can release water via evaporation. This does rather depend on the surfaces surrounding the materials: some are very water permeable, others are not. Exactly how much water transfers between the solids in the house and the air in and around it is unknown - it’s never been measured, as far as I know – but it’s likely to be fairly substantial. If it amounted to a change of just 1% of water by weight, we would be talking about 100 litres of water.

Now on a typical day in the life of a detached house, there is usually between 2 and 4 litres of water vapour suspended in the internal air. Take a house with a floor area of 160m2 (comfortable 4-bedroomed job): it will have around 400m3 of conditioned (heated) air space within. In winter, this will be kept at something like 20°C and 50% relative humidity, which should hold around 9gms water vapour/m3. That equates to 3.6kg or 3.6litres for the whole house. If the relative humidity increases above 75%, you start to notice the atmosphere becoming uncomfortably fuggy and if it gets much higher than this you start to see condensation on hard, cold surfaces, typically glass in windows. Indeed, persistently high relative humidity levels at whatever temperature tend to cause all manner of nasty problems connected with condensation.

A typical household will also be producing water vapour during their day-to-day activities. Humans will give off between 0.5 and 1lt per day each, animals slightly less. Cooking, washing and showering also contribute. In fact you might expect around 5 to 10 litres of water vapour a day to emanate from human activity in a typical working house. It’s still a pretty paltry amount, but it has to be dissipated because if it’s allowed to build up without check, the relative humidity will reach dangerous levels. In fact, our domestic ventilation strategies are predicated on the fact that the No 1 enemy is water vapour. If water vapour is kept at reasonable levels, then all the other concerns like cooking smells, off gassing from solvents, body odour and carbon monoxide poisoning will take care of themselves.

This is the way your winter ventilation strategy is worked out. The external air (let’s say it’s 5°C and 90% relative humidity, it often is) holds around half the amount of water vapour per m3 than the internal air (20°C and 50% RH). The maths is a little complex because warm air takes up far more water vapour than cold air and though the relative humidity levels make it look like there is less humidity in the warm house, the absolute humidity levels tell a different story.

Because the water vapour is floating around in the air, if you swap the internal air for some external air, then you will also be swapping the water vapour levels as well. You are basically sucking water vapour out of the house.

Diffusion is ignored in all this. The fact that there is over a thousand times more water bound up inside the building than there is floating around in its airspace just doesn’t come into the equation, despite the fact that everyone agrees that moisture levels within a building are constantly changing. Doesn’t it seem strange that we should spend so much effort and energy expelling 10 litres of water vapour a day from our homes, when they are 10,000 litres of water already sitting in the fabric?

There are alternative water vapour management strategies out there. The best established one hails from Germany and it consists of fitting highly permeable materials to be used as a reservoir to store moisture, with a view to letting it be evaporated back inside when conditions allow. In Germany, it is seen as part of the Building Biology movement and they regard the use of humidity-buffering materials as one of their key principles. Needless to say, they regard the use of mechanical ventilation as an anathema. A lot of building scientists regard the Baubiologists as cranks, but there was some independent testing of their humidity buffering principles carried out in Canada in 1997 by Straube and Burnett which found that what they called the Dynamic Hydric Response of a wood wool board (Durisol) was excellent. They found that when the relative humidity in the room was increased from 30% to 70%, the Durisol responded by absorbing 7% of its dry mass weight. Straube and Burnett worked out that in a typical situation where humidity was rapidly increased from around 50% RH to 80% RH, the extra water vapour could easily be absorbed by the Durisol board.

It’s not a property exclusive to Durisol. They looked at the water vapour permeability of a whole range of products and estimated the following sorption ratings:

• Plasterboard painted with emulsion - score 40
• Concrete, unfinished – score 90
• Brick, natural finish – score 110
• Softwood, unfinished – score 150
• Strawbale behind lime plaster – score 240
• Durisol board behind lime plaster – score 250

They reckoned that anything with a score of 50 or higher would work as a humidity buffer. They also pointed out that such walls work automatically, don’t break down and require no energy to operate. Unlike mechanical ventilation, of course. Another issue with mechanical ventilation, which is seldom touched on, is that it won’t work consistently in all spaces: there are places within rooms — the classic one being ‘behind the wardrobe’ — which remain largely stagnant and simply never get ventilated. Humidity buffers work by diffusion and don’t require air movement to operate effectively.

The proponents of humidity buffering don’t suggest that it becomes a replacement for ventilation, rather that it’s much more efficient at removing excess humidity from the air inside a house and that this should in turn reduce the requirement for current ventilation strategies. Now take the process one stage further and reduce or remove materials from the house which off gas or contain solvents, and remove the threat of carbon monoxide by having no gas burning indoors, and you have a home where ventilation at half an air change per hour is simply uncalled for.

This way of building in fact brings about an alignment of the interests of the natural building materials crowd and the energy efficiency tyros, two standpoints which have been traditionally been divided over the issue of how to best ventilate a house.

On a personal note, I am hoping that the house we are planning to build next year with Baufritz will be able to push the boat out a little and to explore some of these humidity buffering strategies. Baufritz already use them in the homes they build in Germany but have so far run into a wall of blinkered red tape in the UK. “If it’s not in Part F, you can’t do it” seems to be the mentality here. Maybe with a little coaxing, they will allow us to experiment. I’d like to build a house without mechanical ventilation, without trickle vents and without extract fans, just to prove that it can be done and that indoor air quality won’t suffer and that energy efficiency won’t be compromised. Will it be possible? Watch this space.

Bob Matthews on Ventilation

Good series of articles recently on home ventilation in Selfbuild & Design by Bob Matthews, the oldest surviving selfbuild writer in the business. In June, he summarised his findings. In July, he peered into the future. There simply aren’t that many writers out there who would even know where to begin in handling such an assignment. I hope his readers appreciated it.

What did Bob conclude?

• SAP 2005 presumes a ventilation rate of 4 litres/second/occupant, that’s 14.4m3/hr each. I didn’t know that: it seems quite low. For four people living in a 350m3 house, that’s one air change every four hours. Conventionaly, we’ve worked on around one air change every two hours, but I don’t think there is much evidence that this ventilation rate is actually required.

• That 4lts/sec/person requires 100watts of heat to keep at 20°C above outside temps. So for four people, that’s 400 w. And for double the amount of air changes, that would be 800w. Generally, ventilation systems are set up to move much larger amounts of air than this 4lts/sec/person would indicate, so there is a design inefficiency built into most systems.

• Part F of the building regs suggests that you have a 10mm gap undercut on every door, to facilitate air movement around the house. A lot of people won’t like that because it increases noise transfer.

• The default system of home ventilation is trickle vents for supply air extract fans in the wet rooms. Trickle vents must be 5000mm2 in dry rooms (inlets) and 2500mm2 in wet rooms (outlets).

• Passive Stack Ventilation is one of the main alternatives. Trickle vents stay but the extract fans are replaced by air ducts rising from wet rooms to ridge. Kitchen extract requires 125mm tube, utility room, bathroom – 100mm, WC – 80mm or opening window. It doesn’t work in every configuration – bungalows are not tall enough and room-in-the-roof designs have nowhere to run the ducts, and some critics suggest that it only ever works intermittently anyway.

• Assisted Passive Stack is where a fan is added to the system, to ensure it works at all times.

• Central Extract: very similar to assisted passive stack. One fan in the loft pulls air from all the wet rooms. Works with smaller trickle vents than default, and lower extract rates, but designed for continuous operation.

• Positive Input: in many ways the opposite to Central Extract. Instead of drawing air out of the house, it blows it in, putting the house as a whole under a slight positive pressure. The chief exponents of this system are Nuaire. I’ve been rude about Positive Input Ventilation before, but Bob is much more generous.

• Mechanical Ventilation with Heat Recovery (MVHR): discussed in some detail in recent post. Bob reckons that air leakage should be below 4 q50 (don’t ask – it’s a measurement of air leakage under pressure), which is much lower than we are currently achieving on non-manufactured houses. The current building reg standard is 10 q50, whilst the Passivhaus standard calls for 0.6 q50. Quite a difference. MVHR is the only system here that requires both input and output to be balanced, as they are both controlled by the fan or fans. Everything else is either entirely passive (i.e. no fans) or has fan controlled output or input (only one here). This balancing requirement is a crucial and little discussed feature of MVHR. I suspect it needs adjusting quite frequently but is rarely done.

• Individual Room Ventilators with Heat Recovery: rather than whole house solution, you have a individual room ventilators with a heat recovery capability. Designed for continuous operation.


And what did Bob speculate about in the later article?

• He cast doubt the accepted mantra of the current generation of energy wonks: Build Tight, Ventilate Right. Systems like dynamic insulation (see recent post) mean that airtightness may not be quite the holy grail that it is held up to be.

• Intelligent trickle vents, which self-adjust according to wind speed, air pressure and humidity levels.

• Intelligent controls for mechanical ventilation: at the moment, it’s off/on/boost. In the future, systems may begin to emulate the sophistication now seen with space heating controls.

• Supply Air Windows: Howarth are now making these windows which work by drawing air in between the two panes and pre-heating it on its way into the house. In effect, it’s a sort of heat recovery trickle vent, designed to work with the house under negative pressure, so usually installed with passive stack ventilation, or continuous central extract fan.

• Earth tubes: these draw supply air through underground pipes in order to pre-heat or cool the air before it gets to the house. Much experimented with over the years, but nowhere widely adopted. There are fears about contamination and mould growth within the underground tubes and this seems to hold back more widespread adoption of the technique.

• Dynamic Insulation: the capacity of walls and roofs to draw air in through their structure and to pre-heat it on its travels. A topic covered in a recent blog post here.

In fact, supply air windows, earth tubes and dynamic insulation are all ways of passively pre-heating the supply air. All have great potential but they are all also a long way from becoming mainstream.

I particularly like Bob’s concluding remarks. In the future, we will probably reach more understanding about ventilation processes, and we will be able to design systems more accurately. Then there will be less need to over-ventilate in order to be on the safe side, as at present. There is a need for greater knowledge about the complex issues involved in domestic ventilation. A lot more research is required so that we can create healthy environment in our homes while at the same time minimising the damage we do to the environment as a whole.

There are indeed lots of issues still to be resolved:
• Our understanding of house ventilation seems to be being driven by cold climate countries like Canada and Sweden, where ventilation is more critical. Does their take on it really transfer across to our lukewarm, maritime climate?
• Specifically, is airtightness quite as important as we are being led to believe?
• Are fully passive ventilation systems reliable? Or do we require fans to drive at least part of the system?
• Should we be driving towards more sophisticated controls and sensors in order to balance running costs with air quality? Or is dumb good?
• Are the health concerns about drawing supply air through ducting legitimate, or just a fear of the unknown?

Mechanical Ventilation with Heat Recovery

One of the little discussed details surrounding the Passive House debate is the use and abuse of mechanical ventilation. The Passivhaus standard insists on it: other low energy standards are not so prescriptive. I believe that the way the new Code for Sustainable Homes standards have been drafted, the top levels more or less ape the Passivhaus standard and therefore mechanical ventilation with heat recovery will become de rigeur.

The issue underlying all this is the ever-present contradiction between saving energy and maintaining good indoor air quality. You have to have fresh air inside a home and this fresh air has to be heated (or sometimes cooled) in order for it to remain comfortable indoors. However well you insulate the fabric of the structure, you still have this energy demand to deal with. The energy load naturally varies according to the outside conditions, but it can often be more than 1kW, sometimes even 2kW. That represents around half the overall heat load for the house.

Now the Passive House approach is to first reduce the air leakage of the structure to an absolute minimum. This ensures that you don’t have to heat more air than you actually require. Then you run inlet and outlet ducts around the house and you draw in the fresh air via a heat exchanger, which pulls as much heat as possible out of the exhaust air. This is what is known as a Mechanical Ventilation System with Heat Recovery. The acronym we use in the UK is MVHR.

These air-to-air heat exchangers have been getting more and more efficient over the years and some claim to recapture as much as 90% of the heat from the exhaust air. Also the electric fans that drive them have also been getting more efficient, thus further increasing the CoP (Coefficient of Performance).

Even with a 90% recovery rate, you still need an additional heat source to keep the house warm, but not much. You have reduced the overall heat loss to a minimum. The structure doesn’t transmit much heat, the air leakage is all but eliminated and the supply air is pre-heated by the exhaust air. It’s technically very difficult to do much more than this and this is essentially why the Passivhaus standard is regarded so highly by our energy wonks.

But there are health concerns that have yet to be fully addressed here. Whilst much of the world lives fairly happily with ducted air heating systems, they are not without their problems and issues. And the typical North American home, where this form of heating and air conditioning is the norm, is not built to anything like the airtightness specifications demanded by the Passivhaus standard. What will happen if you a) force people to build to really demanding air tightness levels and then b) force them to use mechanical systems to manage their air supply? We’ve seen a few thousand homes built to these exacting standards in Europe and as yet no one has reported any major problems with air quality. But the UK is proposing to roll out such standards on an unprecedented scale, albeit after 2016. Is this really practicable? Or even sensible?

Take a look at this guidance, emanating from the Canada Mortgage and Housing Corporation recently, on what you need to do to keep your MVHR (which they refer to as HRV) systems tickety-boo. There is a surprisingly long list of maintenance issues to be attended to. Do you really think all UK homeowners will do this? And what will happen if (and when) they don’t?

MAINTAINING YOUR HEAT RECOVERY VENTILATOR (HRV)

Your heat recovery ventilator (HRV) can help make your house a clean, healthy living environment, while keeping fuel bills down. But your HRV can't do all this without your help.
It only takes seven simple steps to keep your HRV happy…

The Seven Steps to a Happy HRV

First turn off the HRV and unplug it.

• Step 1: Clean or Replace Air Filters
Dirty or clogged filters can lower ventilation efficiency. Try to clean your filters at least every two months. Filters in most new HRVs can be easily removed, cleaned with a vacuum cleaner, then washed with mild soap and water before being replaced. Older units have replaceable filters. If your HRV is easily accessible, this is a 5 minute job.

• Step 2: Check Outdoor Intake and Exhaust Hoods
Remove leaves, waste paper or other obstructions that may be blocking the outside vents of your HRV. Without this vital airflow, your HRV won't function properly. During winter, clear any snow or frost buildup blocking outside vents.

• Step 3: Inspect the Condensate Drain
Check to see if your HRV has a condensate drain, a pipe or plastic tube coming out of the bottom. If it does, slowly pour about two litres of warm, clean water in the drain inside the HRV to make sure it's flowing freely. If there's a backup, clean the drain.

• Step 4: Clean the Heat Exchange Core
Check your HRV owner's manual for instructions on cleaning the heat exchange core. Vacuuming the core and washing it with soap and water will reduce dust which can build up inside the core.

• Step 5: Clean Grilles and Inspect the Ductwork
Once a year, check the ductwork leading to and from your HRV. Remove and inspect the grilles covering the duct ends, then vacuum inside the ducts. If a more thorough cleaning is required, call your service technician.

• Step 6: Service the Fans
Remove the dirt that has accumulated on the blades by gently brushing them. Most new HRVs are designed to run continuously without lubrication, but older models require a few drops of proper motor lubricating oil in a designated oil intake. Check your manual for complete instructions.

• Step 7: Arrange for Annual Servicing
Your HRV should be serviced annually. If you are not comfortable doing it yourself, contact a technician accredited by the Heating, Refrigerating and Air Conditioning Institute of Canada. Make sure the technician you call has been trained by the manufacturer of your HRV.

Check Your HRV Balance: the Garbage Bag Test
HRVs need to be balanced, with the fresh air flow matching the exhaust flow. If you do not know if the HRV was balanced when installed or if you have changed or added HRV ducts, you may want to check the balance with the following simple procedure. This rough test will take about 10 minutes.

Use a large plastic leaf collection bag, typically 1.2m (48 in.) long. Untwist a wire coat hanger. Tape the wire to the mouth of the bag to keep it open. You now have a garbage bag flow tester. Go outside to where your HRV ducts exit the foundation.

• Step 1:
Crush the bag flat and hold the opening tightly over the exhaust hood. The air flowing out of the hood will inflate the bag. Time the inflation. If the bag inflates in eight seconds or more, go to Step 2. If the bag inflates in less than eight seconds, turn the HRV to a lower speed, and repeat the test. Then go to Step 2.

• Step 2:
Swing the bag to inflate it and hold the opening against the wall around the HRV supply hood. The air going into the HRV will now deflate the bag. Time the deflation. If your HRV is balanced, air going into the HRV will balance the air coming out of the HRV. The inflation and deflation times should be roughly equal. If you find that the bag inflates twice as fast as it deflates, for instance, your HRV is unbalanced. If you can see no problem with the filters that would cause such an imbalance, you should call a service person to test and adjust your HRV.

Please don't ignore your HRV. Just a little bit of your time is all it takes to keep it running smoothly.

• April or May
— Turn dehumidistat (the adjustable control on many HRVs which activates the HRV according to relative humidity) to HIGH setting or to OFF.

• September or October
— Clean core
— Check fans
— Check condensate drain
— Check grilles and ducts in house
— Reset humidistat (40%–80%)

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.

Who'd be a pressure tester?

I spent yesterday morning with Keith Bartlett who runs a business called Air Leakage Testing based in Saffron Walden in Essex. Keith had a pressure test booked on a renovated house in Greenwich, SE London, and I was getting to ride shot gun with him, picking his brains as we travelled down the M11 in his van with all the kit in the back.

Keith’s background is running a building business erecting steel structures as industrial units. A requirement for air pressure testing for buildings larger than 1000m2 in floor area came into effect in 2002 and Keith took a view that this was the start of a trend and decided, with two partners, to start this new venture to get in on the beginning of a new business opportunity. Together, they have invested something like £150,000, not to mention thousands of hours labour, to get things up and running and they fully expected to be rushed off their feet by now, since the requirement for air pressure testing was extended to new homes in April this year, under the changes to Part L of the building regs.

But it hasn’t worked out quite that way. At least, not yet. Building inspectors have yet to get to grips with the changes in Part L and there is still only a tiny trickle of work coming their way, despite their being less than a dozen firms offering a similar service. In theory, when the new Part L bites, air pressure tests should be carried out on every dwelling type used in a development. That’s a difficult figure to put an exact number to but it must be of the order of 10 to 20 thousand a year throughout the country, not to mention a significant increase in commercial work as well as here the size limit for testing has been reduced from 1000m2 to 500m2. If Keith’s business is typical, it appears that the actual number of air pressure tests being carried out is less than 10% of this figure.

What appears to be happening is that as many as 80% of qualifying commercial buildings are passed by building control without a pressure test. It seems building control are happy to accept “robust details” as an alternative method of compliance, despite there being officially no allowance for this in Part L. This may also prove to be the case with domestic work as well, although the reasons here for slow take-up of pressure testing are to do with the delayed adoption of the 2006 Part L regulations by local authorities.

Thus far the main take up in the domestic sector has been from architects and interested clients who are testing the water and trying to get to grips with the concept air pressure testing. Keith told me: “Architects are in fact often their own worst enemies because the buildings they design are over-complex and full of junctions, just the type of structures that perform badly in an air pressure test.”

The actual test normally takes a couple of hours but there is usually a costly transport element to be taken into account because testers are thin on the ground and one test frequently takes up a full day. So the cost is typically around £300 plus transport for a single house, though it can be much less if there are multiple houses ready to test on the same site. “Most builders feel that they have carried out a reasonable job and are deeply suspicious of pressure testing. If the readings suggest that the house is leaky, they start questioning the accuracy of the equipment. So then we do a smoke test and this shows precisely where the leaks are. Then they believe.”

I was hoping to witness and photograph the test in Greenwich. But the traffic around the Blackwall Tunnel was gridlocked and after sitting in the van for two and a half hours without even reaching our destination, Keith aborted the mission and rescheduled for another day. With more than a touch of irony, I reflected on how the intention of an air pressure test is to save energy consumption, but London’s chaotic road system had ended up with us wasting rather a lot of fuel, achieving precisely nothing. That’s the politics of energy for you.

The Shutters of Old Nice

Nice is famous for its shutters. They form an integral part of the streetscape in the old parts of town, as they do across much of southern France, but in Nice the intensity of the Mediterranean light plus the combination of the pastel shutter shades with the earthy wall colours makes for a quite stunning spectacle. Consequently, the shutters appear on the cover of guidebooks and in countless postcards and have become icons in their own right.

The shutters aren’t just for show. They are immensely practical and are a good example of what we once called appropriate technology, essentially a low-tech solution to a problem, in this instance how to keep cool in a hot climate. The Brinkleys have just spent a week in the apartment I part-own in Nice and, once we mastered just how to get the best out of the shutters, the rooms stayed cool and fresh all day and all night, despite the daytime temperatures peaking in the 30s.

The apartment has a high-tech Daikin air conditioning system and for the first couple of days we played with it incessantly, trying to get it to work perfectly. But air conditioning can be, and often is, frustrating to live with. To get it to work well, you have to close all the windows, but if you then leave it on for a long time, it is easy for the air temperature to drop too low. If you leave it on in your bedroom whilst you sleep, you risk waking up two hours later freezing cold. Even if you manage to get the temperature right — and there are temperature adjustments you can make on the handsets — it is still just a little too noisy to make sleeping easy and, additionally, the air quality isn’t that great because its being recirculated. You keep wanting to throw the windows open to get some fresh air, but of course that defeats the logic of air conditioning.

By Day Three, we had worked out how to get comfortable at night without any air conditioning, just by using the shutters. The shutters have three modes, as illustrated by my photo here, taken from the rear of the apartment.

• Open: lets the light flood in. This also harvests solar energy and heats the apartment in spring and autumn. In the heat of August, this didn’t concern us.
• Closed: keeps the sun out in the heat of the day, provides privacy and blocks out enough light to enable sleep. In addition, a metal hook locks the shutters into the closed position and thus provides security.
• Closed but with bottom flap open: keeps the hot sun out during the day but maximises ventilation.

The trick we learned was to open all the windows and close all the shutters during the night. Additionally, the internal doors had to be left open. This created a controlled flow of air from front to back, enough to keep the apartment cool and fresh throughout the night. No night sweats and no freezing butts, just hours of uninterrupted sleep. In the morning, the fresh bread smells from the bakery downstairs wafted up into the apartment. Bliss.

I can’t say for sure, but I believe that most of the older Nice apartments have been built this way, designed to use the shutters to control ventilation in this fashion. My guess is that this natural form of air conditioning would suffice in all but the most extreme heat waves.

Avoiding bad smells in the bathroom

Anthony Cam asks:
Does anyone have a problem with internal venting? I have used an air admittance valve on my soil stack which has worked fine for the three months since we moved in but we now seem to have smells emanating from the wet floor drain in the shower/toilet and, more recently, from the washbasin in the bathroom. Would an open-vented stack fix this?

Mark reckons:

The probable cause of your problem is the failure of the water traps in your shower and your basin. However, to pinpoint the reason for this is difficult. There are several reasons why water traps fail.

The commonest one is due to something called 'induced siphonage': this occurs when the water in the traps gets sucked down the waste pipes by pressure created by stuff happening elsewhere in the waste system.

Why should this happen in some systems and not in others?

There are a number of identified causes: the waste pipes maybe the wrong size for the appliance, or the individual runs are the wrong length or laid at the wrong fall, or the jointing with the soil stack may be too close to other connections. The best practice notes for what should happen, in an ideal world, in order to avoid these problems are all set out in Part H1 of the E&W building regs, but these are often ignored (they rarely get inspected) and are sometimes just impractical to install in any event.

If the water traps fail, then there is an obvious danger that drain smells will start entering the bathroom. The vented soil stack is a designed as a failsafe in event of the water traps failing: the bad smells will usually take the route of least resistance, being straight up the stack and out through the roof. An air admittance valve (AAV), used more and more widely these days in place of vented soil stacks, does not provide nearly such a good escape path for bad smells; they only open when there is a significant pressure imbalance between the waste pipes and the surrounding house. If your waste traps have failed, the bad smells will be far more likely to seep out through your plugholes than through your AAV, as your traps have now become open pathways for the foul air.

What to do about it? One potential solution might be to replace the AAV sitting at the top of your stack with a full height, open-vented stack, exiting through the roof: it might just do the trick, but it might not. If that doesn't sort it, then you then have to re-plumb the waste runs.

If you do, then consider replacing the existing traps with Hepworth HepVO valves (pictured above and pronounced Hep Vee-Oh), a patented non-return valve which has been on the market since 1997. The HepVO valve system is engagingly simple to understand. There are only three components; the valve itself which looks pretty much like any other piece of pushfit plastic pipe fitting, a straight connector and a knuckle or bend, each available in two sizes (32mmm for basins, 40mm for baths). The innovation is inside the valve where a one-way membrane is stretched across the walls: this allows water and air to pass through it downstream into the waste pipes but stops foul air passing upstream into the house. They are widely available from plumber's merchants (though they sellremarkablyy few, it seems) at a cost of between £12 and £15 a time.

Earlier this year, the BRE (Building Research Establishment, the UK's premier building research body) published an assessment of the product. It was remarkably positive about the valve in almost all applications you could think of using it but one conclusion was particularly interesting: it suggested that when you use two or more HepVO valves in a top floor bathroom, you no longer require either an open-vented soil stack or an AAV stub-stack arrangement.

So if you can get access to the traps that are defective, I would have thought replacing them with HepVO valves would be a very good move.


Self-sealing waste valves for domestic use: an assessment BRE Paper IP5/05 by White, Griggs and Sutcliffe. Mark Brinkley

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