Its is a farce -- test houses should be chosen at random or all houses should be tested.

Air leakage test results are well known to increase during the first few months.

Woolly is a very kind word to use.

I guarantee that six months after completion most new build houses would show a dramatic increase in air infiltration.

It is a joke, HOWEVER how else do you propose it is done? There is no real way, other than to demand every unit is tested on completion and then re-tested after 12 months and bought back up to standard.

It is feasable, but would cost a huge amount of money!

Timber

<blockquote><cite>Posted By: Timber</cite>I guarantee that six months after completion most new build houses would show a dramatic increase in air infiltration.

It is a joke, HOWEVER how else do you propose it is done? There is no real way, other than to demand every unit is tested on completion and then re-tested after 12 months and bought back up to standard.

It is feasable, but would cost a huge amount of money!

Timber</blockquote>

The primary reason being what? Settlement, movement?

Reliance on sticky tape, above all. It only takes a few tiny failures to make a big difference. The first few failures are the significant ones - all the accumulating subsequent ones have diminishing effect. There's no substitute for mechanical clamping. Absolutely drop sticky tape and other adhesive solutions. Uncommonly well-engineered mastic installation may just be OK, longterm.

And reliance on membranes, which are so fragile and can be guaranteed to get at least some tiny punctures, more likely plenty of big ones. Again, it's the first few tiny ones that destroy airtightness - all the subsequent bigger ones have less and less proportionate impact, as the damage is already done. Instead, go for robust, in-depth airtightness e.g. blown-in Warmcel; or wet plaster on masonry, which can be maintained (hairlines filled).

Whatttt? Everywhere, to tape membrane joints, to tape membranes to windows, you name it. No matter how 'high quality', asking for trouble - don't be tempted - ever!

My point in starting this discussion was to ascertain the effect, in a dot and dab constructed property, of cutting a hole of 10cm x 16cm, in the plasterboard, on an external/party wall, on the air permeability of the building that has 'passed' previously, the 10m3/(h.m2) at 50 Pa limit. Can anyone work out the figures?

Just bought 2 tubes of silicone sealant and a can of expanding foam today.

Dominic, if I were you I'd take your expanding foam into your roofspace and seal around where the svp's pipes pass through the ceilings, or seal it from the underside if the svp's haven't been boxed in yet.
Thats typically the worst leakage point.
If not sealed the boxing in acts like a duct linking the ventilated roof void with floor voids, etc and the boxing in is usually open ended behind baths, kitchen units, etc.

Aha - combustion air inlet?

well obviously it'll blow airtightness to smithereens.

Posted By: neiluIs the 10x16cm hole having an electric socket cover fitted?, if so it will have a negligible impact.
With the cover fitted reasonably tightly your only left with the holes in the cover

No, just the first socket/cover will make a great difference to airtightness. 'Only the holes in the cover', if it's the first holes in an otherwise perfect envelope, will make the biggest difference. The next set of holes will make a proportionately smaller difference, and so on. I think we haven't fully visualised the quantity of air that will pour through even a tiny hole, under the air pressures being generated. If it were a visible liquid - imagine the first pinholes arising in the bottom of a boat, the little fountain it would produce, multiply that multifold (because air is far more fluid than water) and project it over hours - the boat's sunk!

Combustion Vent openings are blocked ( taped ) off during the AT test . As are open fires , bathroom and kitchen extractors and other intended vents. The AT test is designed to find "unintentional vents" only - leaks .

So kgr - if we are talking about a vent - it will not affect a test result .

Nope - it's not a vent. It's a fault that happens soon after the new occupier moves in (and usually reoccurs later, even after repairs have been carried out and drying in has ceased) in the usual method of dot and dab construction, in most houses of more than one storey.

Posted By: fostertom

Posted By: sinnerboyit will not affect a test result

but will vastly affect reality.

Not in Regs land . ( I do agree with you Tom )

kgr - given that the company you work for sells a trim to seal the gap between the stairs and the wall then I assume that this is the gap you are talking about. However, given that the plasterboard on the walls does not normally form part of the primary air barrier, then by sealing at this position you will only have a mariginal effect on airtightness, if at all. We have plenty of long term pressure test data to show that secondary sealing is ineffective. We also have plenty of pressure test results following coheating tests which exacerbate the size of the gap between the stairs and wall - even when these gaps are then repaired, air permeability does not improve. The important gaps are those on the primary air barrier - and for walls constructed using PB with dabs on masonry this is the blockwork wall (better still a parged blockwork wall). Anyone relying on the plasterboard on the walls as part of the air barrier is doomed to failure.

Jez

Posted By: DoctorJez We have plenty of long term pressure test data Jez

Dr J - do you have data on return visits - months or better still years later to see how durable an AT result is over time ? If not do you have "a sense" of the type of spec that is most durable ?

sinnerboy

we have data from several years post construction - but only for a few construction forms - some masonry and some timber frame. We also have data from before and after coheating tests which accelerates the normal drying shrinkage and other longer term thermal expansion/contraction processes - but not the settlement effects. The difficulty is in getting access to the same house at a later date. The data from Stamford Brook indicates that masonry constructed using parged blockwork is pretty robust (increase less than 10% over 2 years) - with most of the variability being due to seasonal effects. Wet plastered masonry construction is also likely to be similalry robust. In contrast, the data we have suggests that standard brick-block masonry construction with PB on dabs and without the parging layer on the block work will be prone to longer term degradation, especially if there are built in joists.

Jez