Green Building Forum - PAS2035 & edge thermal bypass Wed, 22 Apr 2026 12:48:13 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 PAS2035 & edge thermal bypass https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285339#Comment_285339 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285339#Comment_285339 Wed, 09 Dec 2020 07:22:43 +0000 cc64
PAS2035 is understandably big on boundaries edges junctions of retrofit insulation. And this is focus of my query.

Have retro fit of early 90s terrace apparently built by apprentices. External walls will have IWI applied. Question is whether to extend this down party walls. I don't really want to do that as the intent for party walls is to apply acoustic solutions so I don't hear quite so much of the neighbors.

Block and brick. Party cavity 10cm will be rockwool filled. External cavity 10cm will be EPS bead filled. Blob and dob plasterboard will be stripped from all blockwork walls before application of IWI to external and acoustic to party walls.

Question is do I need to extend insulation some distance down party wall to prevent thermal bypass of IWI on external wall.

M]]> PAS2035 & edge thermal bypass https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285340#Comment_285340 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285340#Comment_285340 Wed, 09 Dec 2020 09:39:48 +0000 Nick Parsons
I typically return IWI between 150 and 400mm, depending on the specific circumstances.

What sort of IWI will you use? If, for example, you were using dense wood-fibre, that might (I don't know) contribute a bit to the sound-proofing on the 'return' anyway.]]> PAS2035 & edge thermal bypass https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285341#Comment_285341 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285341#Comment_285341 Wed, 09 Dec 2020 10:16:15 +0000 cc64
External wall IWI will be aerogel.

Simply wonder whether the issue might best be addressed by extending a (thinner) aerogel layer down the party wall under the acoustic assembly. Its immobilized air content would contribute to acoustic objectives and obviously also to thermals.

Probably need some PSI (?) figure calculations but where how to get those done; the software isn't exactly open acces]]> PAS2035 & edge thermal bypass https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285344#Comment_285344 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285344#Comment_285344 Wed, 09 Dec 2020 10:28:14 +0000 dathi http://www.ili.co.uk/en/S.R.54-2014.pdf don't know if this one is of any use to you it the irish retrofit standards]]> PAS2035 & edge thermal bypass https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285347#Comment_285347 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285347#Comment_285347 Wed, 09 Dec 2020 11:47:41 +0000 djh Posted By: cc64Has anyone seen a copy of PAS2035
Check to see if it's available through your local library. I find it very annoying that standards like this aren't freely available.

Simply wonder whether the issue might best be addressed by extending a (thinner) aerogel layer down the party wall under the acoustic assembly. Its immobilized air content would contribute to acoustic objectives and obviously also to thermals.

I can't see that that would cause any problems and it's simple. So go for it if you can accept the extra cost etc.

Probably need some PSI (?) figure calculations but where how to get those done; the software isn't exactly open acces

You mean psi values (Ψ) - thermal bridging calculations? If so, the go-to software is Therm and it's freely available.]]> PAS2035 & edge thermal bypass https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285353#Comment_285353 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285353#Comment_285353 Wed, 09 Dec 2020 15:53:28 +0000 cc64 PAS2035 & edge thermal bypass https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285356#Comment_285356 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285356#Comment_285356 Wed, 09 Dec 2020 17:30:17 +0000 bxman
I have a pdf copy of

"PAS 2030:2014 Edition 1
Improving the energy efficiency of existing buildings
Specification for installation process, process management and service provision "


I suspect 2035 may be similar and not that much practical help.

However if that would be of any use PM me and I can email it to you


Have you a quote on the aerogel ?

I would like to try it in some places but have never found a source that I could justify the cost

good luck with the project
cheers Patrick]]> PAS2035 & edge thermal bypass https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285360#Comment_285360 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16838&Focus=285360#Comment_285360 Wed, 09 Dec 2020 19:31:34 +0000 cc64 I have not yet received quotes for the insulation. It's not cheap. Neither is willfully heating the air outside our homes.]]>