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Air test


jamieled

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Only a short update for now and a distinct lack of photos. I'll put something more interesting up in the next week or so. Suffice to say that combining work with trying to get to completion has been quite difficult. Throw into the mix that my other half is shortly due to have twins and you understand why I'm often getting comments like 'do you ever think you've maybe bitten off a bit more than you can chew?'.

 

One milestone recently was getting our air test done. I've decided to write a bit about this as a) There seems to be a fair bit of interest in this on buildhub and b) our result is not quite as I'd hoped and so I thought a few musings on this might help others.

 

I haven't had the actual test report through, but from the results I saw on the screen, we ended up with a value (no laughing please from the passivhaus crowd) of around 3.4 m3/m2/hr. This is fair bit higher than I'd hoped for, but as I'll explain below, maybe not too surprising.

 

The guys who ran the test spent a bit of time wandering round trying to find leaks and allowed me to do the same. There were no areas of the house where they could find significant leakage, but one or two small leaks easily dealt with. This obviously leads to the question of where it's all going. For reminders, our house is built from 300mm I-beams, filled with cellulose and then boarded with OSB on the inside, with all joints taped. All the services are ducted in and the ducts sealed. Windows have expanding foam strips around them and are taped. I don't think I'll ever know where the weaknesses are, but my suspicion is now around either 1) the OSB itself and 2) Where the 1st floor joists meet the outer rim board (a detail I failed to think through before it was too late).

 

If I look back on some of the build, I think that I probably didn't spend enough time figuring out some of the detail earlier on. That said, I had a distinct lack of housebuilding experience when we started, and so I spent a lot of time trying to figure out the basics of drainage, roofing, cladding etc etc... It's now quite clear to me that if I was to have done better on some of these small airtightness details, then I'd have had to either take a lot longer on the build or go down another route (perhaps buying a kit with a minimum guaranteed airtightness?).

 

Anyway, disappointing thought it is, we're in November, it's about 2 degrees outside and the house is toasty and will keep its heat well into tomorrow. While there would have undoubtedly been some benefit in getting it more airtight, it's a lot better than anywhere else we've lived. Frankly, my disappointment was pretty short-lived as we have more important things to worry about. Final bits before I can apply for completion are the access ramp and some outside drainage. Oh, and then the twins might arrive...

 

 

 

 

 

 

 

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11 Comments


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What's your ceiling level detail just plasterboard under trusses? You could possibly address this here

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I was about to ask the same as Russell. We're doing two airtests, at end of 1st and 2nd fix, but the site foreman also did his own test the day before the first official one, just using his industrial vacuum cleaner to pump the air out and feels leaks by hand. Every one we found was in places that would now be impossible to access behind plaster

Edited by joth
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"around 3.4 m3/m2/hr"

Is that based on footprint, liveable, total floor or exposed area?

I can never remember, but seem to think that air tests are exposed area, which makes the losses quite high.

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yes, it's based on the combined exposed internal surface area of walls, ceiling and floor.

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6 minutes ago, Ian said:

yes, it's based on the combined exposed internal surface area of walls, ceiling and floor.

Better get the tape and sealants out.

 

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29 minutes ago, SteamyTea said:

"around 3.4 m3/m2/hr"

Is that based on footprint, liveable, total floor or exposed area?

I can never remember, but seem to think that air tests are exposed area, which makes the losses quite high.

 

Per square metre envelope area.  Does not need to be exposed so could be party wall, party floor, basement etc.

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2 hours ago, Russell griffiths said:

Have you had this done after plasterboard, I’m thinking of doing mine beforehand so I can remedy anything. 

Any thoughts. 

 

Yes, do it before you board if you have a challenging target.  MBC do this as standard.

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good luck with the twins, when they are older, if they are anything like mine, the doors will always be opened anyway.

 

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11 hours ago, Russell griffiths said:

Have you had this done after plasterboard, I’m thinking of doing mine beforehand so I can remedy anything. 

Any thoughts. 

After plasterboard, which I regret now. If doing it again I'd definitely do 2 tests, they don't cost much in the grand scheme of things.

 

We did spend a lot of time going around the main structure on windy days pre plasterboarding but it obviously wasn't up to much.

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As documented before cheap radiator fan inserted into a sheet of OSB covering a window will more than exceed any blower door fan pressure. 

 

Use the back of your hand for the big holes and a candle inserted in a length of  electrical conduit to nail any small leaks. 

 

A diligent sweep of the house will get you above or beyond passive levels. 

 

For awkward spaces airtight sealant

 and/or airtight paint will remedy most things. 

 

I'd be surprised if the OSB is causing the issues assuming the cellulose is dense packed behind it. 

 

Also don't loose too much heart. Your reading could mean totally different things for different shapes and sizes of houses and the natural sheltering externally has a very large impact also.

 

 

IMG_20201129_163707.jpg

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