After some help on airtightness approach

[Selfbuildnewbie]

We are midway through our build and have started adding the plasterboard etc so quite a way along and airtightness has been an afterthought.  Before we finish boarding up, I just want to get a sense of whether what we're doing is sufficient or whether there is anything else we should be doing that would significantly improve the airtightness (at this stage, I don't want to do things that would only give little gain)

 

What we have done / are planning to do:

 

• We are adding OSB boards to the underside of the first floor ceiling and sealing all joins with expanding foam. We're then painting the entire ceiling with Passive Purple paint to form the airtight membrane. We're going to lap the passive purple paint onto the external ICF walls to ensure airtightness where the first floor ceiling meets the external walls.
   
• Compression glands have been installed around cables as they pass through the heads of studs. I don't think we can easily apply passive purple paint around these glands on the underside of the ceiling because the internal stud partitions are in the way, so is it worth us applying purple paint on the cold side of the attic?
   
• We haven't done anything about airtightness around the spot lights in the first floor ceiling - what would people suggest?
   
• On the ground floor, the gap between the screed and the external walls has been filled with expanding foam, which has been cut off flush and then sealant applied to form an airtight seal. Do we need to go any further and apply passive purple paint as well to this wall/floor join or is foam and sealant sufficient?
   
• The same goes with penetrations through the screed for services and drainage. We've applied foam and sealant. Does this need anything else?
   
• Airtightness tape will be installed around windows.  Again, it's been suggested to us that we apply passive purple paint on top of the tape but not sure whether this would give much added benefit?

 

Anything else we should be doing?

 

[Redbeard]

Forgive the Q if the answer is too obvious, but you say ''the gap between the screed and the external walls has been filled with expanding foam''. Was this air-tight foam? AIUI All air-tight foam is claimed to be air-tight (of course!) but not *all* exp foam is air-tight. I would not bother is *air-tight paint* over *air-tight tape* unless you feel some of the adhesion is less than 100%

 

 

[Selfbuildnewbie]

@Redbeard - just went over to site to check. 

 

Contractor has used Soudal expanding foam: Soudal Expanding Foam Gun 750ml | GB DIY Store

 

And then he's gone over the top of the foam with decorators caulk.

 

[Redbeard]

Soudal do an air-tight foam. The one you link to does not claim to be. Decorators caulk I suppose could be, but a lot depends on adhesion, substrate etc. I think this may be somewhere where you use Passive Purple as 'belt and braces, but see if others agree.

[Mike]

7 hours ago, Redbeard said:

Soudal do an air-tight foam. The one you link to does not claim to be

Agreed, the one you've linked to isn't. If you stick with Soudal, you'd want this one - Soudafoam Gun Win. & Door SWS. which is not only air-tight, but flexes if the joint moves to maintain the seal. Personally I'd remove the foam and do it again.

[Thorfun]

Why don’t you get an Airtightness test done to see where you’re at at the moment before throwing more money at it? It might be that you’re happy with the level of airtightness already achieved. 

[joe90]

4 minutes ago, Thorfun said:

Why don’t you get an Airtightness test done to see where you’re at at the moment before throwing more money at it? It might be that you’re happy with the level of airtightness already achieved. 

+1, my test showed up a number of “leaks” I was not aware of and enabled me to work on them prior to finishing. 👍

[Selfbuildnewbie]

How much do those airtightness tests typically cost?

[Thorfun]

2 minutes ago, Selfbuildnewbie said:

How much do those airtightness tests typically cost?

we paid £300. don't know if that's a lot or not but it was the going price around here. and as @joe90 said it showed up leaks that we fixed there and then and which brought our score down. it was quite interesting to see the score drop after each remediation. instant feedback.

[joe90]

Mine was £250 and he spent ages with me.

[SteamyTea]

6 hours ago, joe90 said:

Mine was £250 and he spent ages with me.

I took a video of it, think I posted it up here somewhere.

 

There is a topic about making a DIY blower in here.

It is basically just a fan fitted to a board, then fitted in a window opening.

[joe90]

I was going to buy a vape but then they were expensive and no disposable ones so I used joss sticks to find where the air was coming in 😇.

[SteamyTea]

27 minutes ago, joe90 said:

I was going to buy a vape but then they were expensive and no disposable ones so I used joss sticks to find where the air was coming in 😇.

I would have filled your house with smoke quiet happily.

And I did not remember, at the time, to mention the huge leak around the WBS air inlet.