MBC PH Second Air Test

[MartinI]

We are self-building/managing an MBC Passivhaus near Norwich, just starting plaster-boarding. We are aiming for Passivhaus Certification.

 

Our first MBC air-test was okay, 0.47ach, despite (and it seems others of you have a despite) there being a couple of areas where air-tightness could have been better.

 

Having remedied these areas, and been diligent about sealing penetrations, I'd anticipated an improved result, however our recent second air-test wasn't to the required Passivhaus standard of 0.6ach. We checked what we could with a smoke pen, but couldn't find anything significant.

 

Has anyone had similar circumstances, and did they manage to discover why? I'm applying additional taping to window reveal corners, in the hope that this is enough.

 

thanks in anticipation.

[Russdl]

What shape is the building? Has it got dormers? Has it got a chimney? 

 

You say you are just starting to plasterboard, I think you need to find the problem first otherwise you could bury it under plasterboard and then it will become very difficult to fix.

 

MBC guarantee 0.6ach or less so it should be their problem. You say it was 0.47ach so perhaps MBC had done all that was required of them and subsequent trades have knocked a few holes in it?

 

Oh, and welcome to BuildHub.

[Thorfun]

I'm no expert but I would ask the question, what has changed since getting the 0.47ach result? primarily focusing on the external fabric of the building.

[NSS]

Must admit I've wondered about the MBC air test timing, and whether people then use it as their as built SAP calculation when presumably a lot can change once they've left site and other trades move in. It's one thing to guarantee a near air tight box, but another to maintain that level through first and second fix.

[scottishjohn]

15 minutes ago, NSS said:

It's one thing to guarantee a near air tight box, but another to maintain that level through first and second fix

this will be why MBC do it at that stage --you and they  then know that the problem is not with the house shell but the trades after them

soidf doing another test it would bebetter to do just prior to PB fater all services are in -so its easy to remedy

 

[NSS]

6 minutes ago, scottishjohn said:

this will be why MBC do it at that stage --you and they  then know that the problem is not with the house shell but the trades after them

soidf doing another test it would bebetter to do just prior to PB fater all services are in -so its easy to remedy

 

 

Appreciate that, and agree a test before plaster boarding is sensible. However, my point was that an air test on which an 'as built' SAP calculation is to be based should be conducted when it's built - fully built, even if that's a second or even third test. Anything based on an earlier test could be some way off reality.

[joth]

9 hours ago, NSS said:

 

Appreciate that, and agree a test before plaster boarding is sensible. However, my point was that an air test on which an 'as built' SAP calculation is to be based should be conducted when it's built - fully built, even if that's a second or even third test. Anything based on an earlier test could be some way off reality.

This is rampant across the industry though? You hear of big developers failing the test (on the odd house actually tested) so the squirt sealant under all the skirtings so it passes. Then next day the carpet fitters arrive and cut the sealant all out again

Honestly no idea how to avoid it really. Airtightness is so hard won and so easily lost,  the homeowner can easily destroy it the day they move in without even realising they have. 

[Gone West]

Hi and welcome to the forum. I have found that the airtightness test results can be affected by how windy it is and the wind direction. The chap who did our airtightness test wanted to use the house door inside the front porch because it was unaffected by the wind.

[NSS]

1 hour ago, joth said:

This is rampant across the industry though? You hear of big developers failing the test (on the odd house actually tested) so the squirt sealant under all the skirtings so it passes. Then next day the carpet fitters arrive and cut the sealant all out again

Honestly no idea how to avoid it really. Airtightness is so hard won and so easily lost,  the homeowner can easily destroy it the day they move in without even realising they have. 

 

I wasn't talking about big developers (sure we all know they're results will be 'questionable') but self-builders. What's the point in kidding yourself that your house is more air-tight and hence more energy-efficient when it's you that will be paying the bills?

[scottishjohn]

3 minutes ago, NSS said:

 

I wasn't talking about big developers (sure we all know they're results will be 'questionable') but self-builders. What's the point in kidding yourself that your house is more air-tight and hence more energy-efficient when it's you that will be paying the bills?

how much is an air test ?

 

[recoveringbuilder]

1 minute ago, scottishjohn said:

how much is an air test ?

 

£250 we paid 

 

[scottishjohn]

19 minutes ago, Christine Walker said:

£250 we paid 

 

so Isupose the question is --how long would it take to recoup the cost of the test ,if the difference was little between tests

 

[NSS]

2 minutes ago, scottishjohn said:

so Isupose the question is --how long would it take to recoup the cost of the test ,if the difference was little between tests

 

But how do you know it's going to be little if you don't do a test when the house is complete? And it may not just be additional energy costs, it could affect the air quality provided by the MVHR (which was critical in our case). Also, in the context of the OP's situation, failure to meet the required ACH rate for passivhaus may not just mean losing the certification goal but needing heating where none may have been provided. 

 

 

[ProDave]

I tested mine (DIY) as soon as I had finished the air tight membrane and taping.

 

By that point all first fix penetrations were complete and sealed up.

 

From that point on i have done all the internal work and that has not involved any more penetrations through the building so I can be pretty sure it would still give the same result.

 

I think this is the first time I have heard of anyone getting a second test done. I am pretty sure everyone else just used the MBC test for their as built SAP.

[scottishjohn]

16 minutes ago, NSS said:

But how do you know it's going to be little if you don't do a test when the house is complete? And it may not just be additional energy costs, it could affect the air quality provided by the MVHR (which was critical in our case). Also, in the context of the OP's situation, failure to meet the required ACH rate for passivhaus may not just mean losing the certification goal but needing heating where none may have been provided. 

 

 

If you are not building it yourself -

-then no you don,t know 

If you are finishing off after first test -then you should know

Edited June 28, 2020 by scottishjohn

[NSS]

3 minutes ago, scottishjohn said:

If you are not building it yourself -

-then no you don,t know 

If you are finishing off after first test -then you should know

Depends on how hands on you've been. Remember, not every self-build is self built.

[joth]

1 hour ago, NSS said:

 

I wasn't talking about big developers (sure we all know they're results will be 'questionable') but self-builders. What's the point in kidding yourself that your house is more air-tight and hence more energy-efficient when it's you that will be paying the bills?

Absolutely. I actually thought you were talking about self builders that only care about passing SAP and don't believe airtightness has any other value except box ticking. (IIRC someone was expressing this opinion on here just this week)

 

[NSS]

36 minutes ago, ProDave said:

I tested mine (DIY) as soon as I had finished the air tight membrane and taping.

 

By that point all first fix penetrations were complete and sealed up.

 

From that point on i have done all the internal work and that has not involved any more penetrations through the building so I can be pretty sure it would still give the same result.

 

I think this is the first time I have heard of anyone getting a second test done. I am pretty sure everyone else just used the MBC test for their as built SAP.

 

Which is all well and good if, as you have Dave, done all the work yourself or if you've personally overseen it all. My point is that's not the case with a lot of 'self builders'.

[MartinI]

Thanks to all, I must admit that I hadn't expected so many responses so quickly, if I had, I would have been online sooner.

 

To add a little detail, I am a Certified PH Designer, and I have been studying PH for more than a decade now. I'm not being all that hands-on, it would slow the build, though I do tend to be on site about 4 hours most days keeping an eye on things and doing what I can.

 

To respond to Russdl: I made sure that our house is a pretty simple box shape, with a side lean-to construction (the latter basically a planning requirement) - no problematic dormers or chimneys. We are building at Long Four Acres. We'd love to find the reason for the loss in performance before proceeding, but we cannot really afford to delay the trades. The impression we got is just that a lot of what was okay previously, is a bit less okay now; thus it is a lot of small issues rather than any major one.

 

Thorfun rightly asks what has changed since the MBC. 1) I put conduits through the wall for power and other services, these all had grommets; Some conduits have now been permanently sealed, others had a temporary seal for the test 2) MBC cut lots of holes in the ProPassiv board to blow in the cellulose, the discs were replaced and well taped in. 3) Two windows had to be replaced, these were taped in at least as well as the original windows; however a pane wass cracked during this exercise, and is yet to be replaced. 4) AGD is as yet incomplete, but again was carefully taped. These were all checked with a smoke pen during the test and other than small leaks nothing untoward was found. But I am now adding SL tape to seal the small leaks.

 

I had rather assumed it was required to do an as-built final test for BC, but perhaps if one betters 0.6 early on then it is rather a given. It's disappointing not to find others who have done second tests.

 

Personally, if we had time and funds, it would be best to stop work, reseal everything and retest - but this isn't really something I can do. Perhaps if our second test had been terrible... but actually it's around 0.8, so I'm reasonably confident I can get it back under 0.6 - it would just be good to be certain.

 

Oh, and more leakage is a moisture in the walls issue as much as a need for extra heating.

 

thanks all

[ProDave]

Make your own blower door with the largest fan you can find (I used a butchered old desk fan) then you can spend as long as you like going around looking for leaks with a smoke pen

[Dreadnaught]

41 minutes ago, MartinI said:

AGD is as yet incomplete

 

What is AGD? Google suggested it was wither Agricultural Drain or Australian Geodetic Datum.

[Pete]

2 hours ago, ProDave said:

I tested mine (DIY) as soon as I had finished the air tight membrane and taping.

 

By that point all first fix penetrations were complete and sealed up.

 

From that point on i have done all the internal work and that has not involved any more penetrations through the building so I can be pretty sure it would still give the same result.

 

I think this is the first time I have heard of anyone getting a second test done. I am pretty sure everyone else just used the MBC test for their as built SAP.

Had my test done early when all windows were in but before plasterboard. Got a test result of 0.47 if I remember rightly with a big trim missing off my sliding windows so was quite happy even though I was miffed as it could have been lower. The air test people said they needed to come back to do another test when it was finished costing another £200 ish. I contacted my BI and asked do I need to do another test as he had never had such a low result before seen as I was doing all the work and he replied he was happy with just one test. I might add he already knew I was quite an anal self builder and would not be doing anything to jeopardise my airtightness result. Some may add it would be worth doing another test just to prove nothing had been done that would lower my result but I am happy with my efforts in being meticulous with sticking!!

[Gone West]

2 hours ago, MartinI said:

It's disappointing not to find others who have done second tests.

Both of our airtightness tests resulted in 0.47ach and the tester spent half a day each time at a cost of £200 per morning.

[Thedreamer]

If you are going for a fairly standard build, do you typically test at the end? We were supposed to have an air test before locked down but it got put off and we are now pretty much completed inside. 

[MartinI]

For AGD I meant Above Ground Drainage ?