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Do I need an air tightness test??


selfbuildrookie
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This is probably a stupid question but... I assumed an air tightness test would be the norm at the end of our new build project, but both builder and architect seem to think not. Google suggests it *is* a requirement on new builds. Can anyone advise if it’s a standard requirement for building regs or not?

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Air pressure test can be avoided for a single house but the SAP assessment must use the default air infiltration rate of 15 - unless accounted for at the design stage this will probably result in Building Reg failure (CO2 emissions and fabric efficiency). Compare this value to some of the numbers achieved by members on here of 3 or lower! I regularly see values of about 7 with masonry construction and standard levels of workmanship/detailing.

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There are only two cases where you don't need to do an airtightness test:

 

The first is if the house is part of a small development where no more than two houses are to be built, and where the builder has demonstrated compliance on another house of the same type, with a pressure test, within the preceding 12 months.

 

The second is if a default value of 15m³/h.m² at 50 Pa is used when calculating the DER.

 

The first case almost certainly doesn't apply to most self-build, I suspect, and the second case will be challenging to meet, as it implies a pretty dreadful air permeability level.

Edited by Jeremy Harris
Cross-posted. . .
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6 minutes ago, MikeSharp01 said:

By challenging I guess you mean easy to achieve such a leaky building if you were trying but with this level of leakiness other things around building regs etc fall out of bed?

 

 

Yes, challenging in the sense of the impact it will have on meeting the overall requirements in Part L1a. 

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Yes you will need a test. But look at this as a positive. If you choose a sensible person to do the test they will do it in two steps. In our case this flagged up leaks which I had not spotted but could be fairly easily resolved before a second, final test. That being said we didn't achieve quite what we wanted.

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Thanks all. As I thought, yes we do need a test - and I'm very happy about that as we are seeking to achieve 2m3/hr/m2. The builder's reluctance is a slight red flag, but we are very early doors with the build so plenty of time to make it clear that we certainly will be having a test at the end, and I am looking forward to seeing what we will have achieved!

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Our build company provided a guarantee that the house would be 0.6 ACH at 50 Pa or less ( they actually achieved 0.43 ACH @ 50 Pa when the house was tested).  The final payment of 20% of the total contract price was dependent on them meeting this requirement.

 

I'd be inclined to try and get a builder to contract to meet the spec you want, TBH, just to save pain and grief down the line. 

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  • 2 years later...

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