25 Nov 2009

The end of Replacement Dwellings?

It’s been a sort of unwritten principle of planning that replacement dwellings were not very contentious, at least in principle. Planners would set limits on any increase in size, which caused angst for lots of people wanting to replace a clapped out 1930s bungalow with a six-bedroom, four-storey gin palace, but the principle that you could knock down your home and replace it with something more to your choosing was never in doubt.

No more. Various local authorities are now taking a view that if your plot is of sufficient size, then you will have to replace your home with more than one – usually three, as this also triggers an additional requirement for at least one to be affordable.

This new state of affairs came to light when some old friends asked my advice about buying a 1930s bungalow with a view to replacing it. They didn’t even want to increase the footprint – they were perfectly happy with the size of the existing bungalow – but they wanted a building that wasn’t mostly asbestos, and one that was properly insulated. They even quite liked the design of the existing house and were perfectly happy to build something like a replica. What they really coveted was the large garden.

Yet their initial contact with the local planners suggested that they wouldn’t be able to do this because the garden was sufficiently large to trigger the affordable housing quota, and that if they wanted to rebuild, they would have to build two private homes plus an affordable one. Which, of course, they don’t want to do.

What a strange state of affairs? They are free to buy the house as is, and to enjoy the garden. They can improve it, extend it even, but they can’t rebuild it without losing the garden.

Has anybody else come across this policy? Any suggestions on how to counter it?

20 Nov 2009

Decide in haste — repent at leisure

Blimey. I am ever so slightly flabbergasted by the response to my last blog post on mechanical ventilation with heat recovery. I thought it was rather obscure and just a little boring, but thus far I’ve had ten responses and just about everybody disagrees with me. And what’s more, they all seem so anguished. Can it be that this is actually a very critical topic, and that what we are confronting here is a crucial issue? And why do commentators feel so threatened when I question the Passivhaus orthodoxy?

All I am saying is that I am not yet satisfied that the airtight/MVHR build route is the “way to go” for all new homes. I’m not set against it; I’d just like it to be tested in lots of real life UK situations before we embark on it as mandatory. I don’t think it’s that time critical. A delay of three or four years is nothing compared to making a horrible mistake. If this was a drug trial, we would be spending five years and billions of pounds putting it through its paces: why should we accept any less from a critical element of our future wellbeing and future build costs?

As the last respondent put it:

We cannot afford further delays.

I think we can. I don’t think the ice caps will melt any faster if we stand back and assess for a little while, rather than charging in.

16 Nov 2009

Whither MVHR?

An interesting letter in last week’s Building from Tim Gough who has a CV as wide as a Passivhaus wall.

In it, he berates the Zero Carbon Hub for being no such thing. They are courting compromise in asking for the mandatory use of mechanical ventilation with heat recovery (MVHR) to be ditched. They say here that is a step too far for a temperate climate like the UK. Problem is that without MVHR, you can’t really build to PassivHaus standards because it’s so airtight that you would keel over every time someone farted.

Passivhaus standard uses just 15kWh/m2 for annual space heating requirements. Zero Carbon Hub are suggesting that this is relaxed to somewhere between 30 and 45kWh/m2 – i.e. two to three times as much, which is about as low as you can go safely without MVHR. And is really not much lower than where Part L will pitch us next year.

Maybe this debate is a bit obscure, but it’s nevertheless interesting. I rather tend to side with the Zero Carbon Hub on this. I think mandatory MVHR is just possibly a step too far in the UK. If you look closely at Tim’s text, you can begin to make out just what the problems are.

This is not a question of diminishing returns – to halve or quarter heating/cooling costs by means largely of a MVHR system costing a few thousand pounds can hardly be said to be that writes Tim.

Except that it ignores the cost of running the fans which drive MVHR system. OK, they are low. We now have fans operating at under 100w, but multiply that by the 8760 hours in a year and you have consumed enough power to heat and cool 58m2 of Passivhaus. The actual energy saving achieved by MVHR is therefore pretty minimal. Some commentators have even suggested that it’s not a net energy saver at all. They certainly aren’t if residents are so bold as to open their windows.

MVHR systems do not, contrary to what is claimed, adversely affect indoor air quality – even if the filters are not cleaned.

That is true. The reason Passivhaus insists on them is because of air quality, not energy saving. The problem is that they don’t always work as planned; they break down; people turn them off (ironically sometimes to save energy). That is where the problems may lie.

Housebuilders worry about reliability, but this is a proven technology that is no more complex than an extract fan.

And extract fans never break down?

What, I wonder, is the real agenda of the promotion of these poor standards?

In a word, caution. What ought to happen is that several hundred new homes should be built to PassivHaus standard, complete with MVHR systems installed, and then lived in by ordinary folk for something like five years. That would be a sensible test of whether the system is workable. If the MVHR systems proved to be reliable and popular and people learned to live in the houses the Passiv way (i.e. not opening windows), then MVHR could be safely rolled out as a mandatory building regulation requirement in new airtight homes. But until that’s done and dusted, making MVHR mandatory would be pretty rash. Stupid even.