Expected Airtightness in New Timber Frame House

C

cabol

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I'm building a new timber frame house and would like to go for a HRV system. What puts me off is the extra costs associated with providing service cavity, airtightness membrane, possibly eco joists etc.

If I was to go ahead with current build method (timber frame with insulated plasterboard on inside) and maybe pay extra care to sealing around windows and doors does anyone know;

(1) What level of airtightness could I expect to achieve? and
(2) Would this be sufficient to get some benefit from a HRV system?
 
Hands up: vested interest: see my profile.

The service cavity is a pain.....but actually, it's not !

Whether you use a HRV or not - you're going to need a membrane anyway, so that extra cost is here to stay, no matter what. That's what the new regs have done for us. And, tbh, it needed to be done. Our houses, generally, are like sieves. Conventional and open frame ones, at any rate.

Now, even if you do get it all intact, and then your electrician or plumber puts a hole in it later, to pass a service through, your airtightness is gone. This is because your TF is an empty void, inside. A closed panel system (like ours), doesn't need a membrane anyway and hanging stuff on the wall panel inside, doesn't nullify it's airtightness properties.

I don't believe it's worth NOT doing the membrane - the 'risks' are too high, and you'll only get ok-to-poor results. I'd expect you to default close to 10m3/hr/m2, but I stand to be corrected based on your attention to detail, and the quality of the slabbing and wiring. The fusebox location is a classic for air leaks !

Another big cause of airtightness leaks is the way the joisting is done. If carried over the header plate of the GF wall, and even if there's a rim-beam, across their ends, it's a nightmare to seal. Add in downlighters to the ceilings and you might as well open the windows..........in other words.....you'll have to seal the ceilings as well........:eek: And yes, there is another way of doing it, to avoid this messy junction.

Most recent blower test on one of our houses - no membrane, no plasterboard, no ceilings (yes, open to the bottom of the roof), floor screed in, windows/doors and key joints taped - gave a reading of 0.9m3/hr/m2. His BER assessor is estimating another 20% gain with linings attached. In anyone's book, that's very good.

I've seen another, without the screed in, again, no plasterboard, no ceilings, and no membrane, and it came in at 2m3/hr/m2. The issue there is the accuracy of the raft, and the need to grout and seal it. Still good, though.
 
Hi We are currently doing a closed panel timber frame house, supplying windows doors etc. We are deciding whether to go for the additional Air Tightness membrane in the upstairs ceiling, are you saying if the plumber needed to put a pipe in from the attic or spotlights in the ceiling does this mean the air tighness is gone. Are we better off leaving it out or will it be a benefit. Thank you
 
yes, you're airtightness is, not completely gone, but very compromised. It's all down to how accurate and tidy those guys are. Pipes need to be sealed, but downlighters -that's a real problem.

You can't just ignore airtightness, as it'll manifest itself in your fuel bills.......

First, you cannot have insulation anywhere near those lights and transformers (I'm presuming that's the type you're using). So you will have both holes AND no insulation (Fire issue). I have them in my house, and I really, really regret them...:eek:

If you're using LED downlighters, it's a bit better.
 
The trouble with the little boxes [very neat installation BTW] is that they cannot both protect the transformers and be sealed. The fire risk comes from the build up of heat.

ONQ
 
onq said:
The trouble with the little boxes [very neat installation BTW] is that they cannot both protect the transformers and be sealed. The fire risk comes from the build up of heat.

ONQ
Click to expand...

Tks, but you're incorrect - they are not airtight, and they are not small - they are considerably larger than the off-the-shelf hat you can buy.

You're forgetting that in a 'conventional' situation (e.g. in a GF ceiling), they are mounted between joists and under a floor, over. Mine is made from a Class 0 fire-rated material, of a standard of protection, higher.
 
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