Thursday, July 28, 2005

Radiator Sizing

Jonathan Ackers asks:

"Is the latest building reg compliant house really that much warmer than, say, a 30s-built house? I was chatting to my plumber mate about how many radiators we'd need and he uses a rule of thumb method acquired years ago, but surely this has changed significantly in our new super-insulated world !?"

Housebuilder's Bible author Mark Brinkley reckons:

If you carry out specific heat loss calculations on pre-insulated housing and on housing built to current standards, the theoretical results show that the overall space heating load has been reduced by around two-thirds. A 1930s semi requires around 100 watts per m2 to keep temperature 20°C higher than outside: a house built to 2002 standards should require about 35 watts per m2.

That doesn’t have any bearing on the number of radiators but it should reduce their sizing considerably. In theory, you could reduce radiator sizes by the same factor (ie two thirds), but running counter to this is the uptake in condensing boilers which like to work at lower temperatures. Whereas traditional radiator based systems are were designed to work at a 50°C temperature difference (between the flow temperature and the room temperature), condensers work better at a 40°C difference, which reduces temperature output from radiators by 25%. Taking this into account, an efficiently-designed modern radiator system should still work fine with radiators half the traditional size.

However, plumbers run the risk of being sued if the system doesn’t deliver enough heat and therefore caution is the watchword. Whilst people won’t notice radiators which are oversized, they will complain like stink if they think they are undersized, so many plumbers continue to use traditional rule of thumb calcs for all the homes they work in. After all, how does the plumber know whether a house has really been built to 2002 standards?

If you can only see this single article on screen please click on the 'Housebuilder's Update' heading (screen top left) to view the rest of this month's items and have access to our archives.

Property developing- can you climb the property ladder?

Can You Make a Living Building One House a Year?

It’s a reasonable question. Many people, usually non-builders, are attracted by a lifestyle built around the notion that you can. Maybe you have a little capital saved up, inherited or locked up in a house; use that to buy building plots and borrow to build and live off the profits. How would it go? Perhaps £100,000 needed to get up and running, another £100,000 borrowed to finance the build and live off the £50,000 a year profits.

Actually it’s a very appealing prospect, which is the main reason it’s so hard to achieve. There are many others sharing the dream, along with countless selfbuilders who may not even be bothered that much by the price of the land. All this competition pushes up land prices and scuppers the business plan.

Twenty years ago there were many small businesses active in this market but the tide seems to have turned against them.

In 1983 there were nearly 30,000 NHBC builders (registered with the trade body the National House-Builder's Council), only half of whom built a house in any given year. Today there are just 15,000 NHBC builders.

In 1983, 10,000 NHBC builders were building fewer than 10 houses a year and contributed 15 per cent of new homes. Now there are just 4,000 builders this size and they contribute 8 per cent of output.

In contrast, the output from the Top Twenty housebuilders has increased year on year. The way land is now released – i.e. in great big chunks – plays into their hands: they have land purchasing teams working on optioned land five, ten, even fifteen years out. The small builders are left with the scraps and the scraps are getting thinner and thinner.

So, whilst the model remains an attractive one, the reality is that it’s extremely hard to put it into practice. There aren’t enough small plots around for it to be economically viable.

Wednesday, July 27, 2005

No More Door Closers - Yippee

We building regs watchers are well used to consultation documents spewing out of the ODPM. Building control these days is in a state of permanent flux and it is almost impossible for professionals to keep up with all the changes and amendments. Part B deals with Fire Safety and it’s constantly being tinkered with but now we have a new consultation paper in front of us, in effect a full-blown rewrite. This morning I checked into the ODPM website to see what the action was. It’s there, under Consultation Documents; Part B has been separated into two sections, one for dwellings, the other for everything else. So far so good: my interest is dwellings, so that might be half my work done. But then I download Part B consultation for dwellings and find that it’s 236 pages long. Oh, my Gawd.

Already I can feel my eyelids getting heavy at the thought of trying to digest any of this. But, I had been alerted in the press that there was an interesting nugget in here and, after a bit of digging around, I found it on p203.

"The Office of the Deputy Prime Minister is minded to remove the need for self-closing devices within
dwellings. This is because they can present a hazard to children; they can
interfere with the day-to-day convenience of the occupants and many of
our stakeholders tell us they are often disabled soon after occupation. The
fire safety benefits of closing doors, particularly at night, remain and it is
proposed to reinforce this message through national and local Community
Fire Safety programmes (see and other fire safety
initiatives. We would therefore particularly welcome consultees’ views on this particular proposal."

No more door closers! Yippee! That’s my view, ODPM.

What a pain in the arse they have been. I well remember back in my loft-converting days in the 1980s that we carried Perko door closers (pictured at the top of this blog) in our tool kits. They were a complete bugger to fit and, if adjusted over-strongly, they would snap your hand off when they door slammed shut. They would be fitted into the designated fire doors until the building inspector finalled; and then they were whipped off, by order of the client. My guess is that I fitted the same Perkos about six times before some Muppet decided they actually wanted to keep them.

What the other 235.5 pages have in them, I have no idea. But this one proposal certainly meets with my approval. Mark Brinkley


Monday, July 25, 2005

Why Americans Build Big Houses

Pick up an interesting snippet from the Washington Post, via The Week, which I subscribe to. It says that US houses have grown by 55% in floor area in the past 35 years. Today average US house size is 2330ft2, which means, if my maths is right, that in 1970 it was 1500ft2. Jeez: that's just an enormous figure for an average house size. I think the UK figure is around 800ft2, a third of the US size. I know that everything is bigger in the US, but that's a gob-smacking statistic. It's as though the obesity crisis has grown to encompass housing.

Larger houses may sound fine and dandy but they do nothing at all for energy efficiency: in fact, energy usage is closely correlated to floor area. I sometimes come across people asking me about building "in a sustainable way" or advice "on building an eco house." The answer is short and simple. Build small. Live light. Don't collect piles of rubbish that need extensions just to house. I suspect that this, more than anything else, is behind the huge explosion in US house sizes: they have to have someplace to fit all that junk that they keep importing from China. Mark Brinkley