Green Building Forum - Celotex shrinkage and warping Sun, 10 May 2026 21:42:25 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Celotex shrinkage and warping https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279357#Comment_279357 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279357#Comment_279357 Wed, 11 Mar 2020 20:25:29 +0000 RussellNewall Has anyone else experienced this ?]]> Celotex shrinkage and warping https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279366#Comment_279366 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279366#Comment_279366 Thu, 12 Mar 2020 08:35:23 +0000 GreenPaddy Celotex shrinkage and warping https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279369#Comment_279369 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279369#Comment_279369 Thu, 12 Mar 2020 09:45:29 +0000 Jeff B Celotex shrinkage and warping https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279370#Comment_279370 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279370#Comment_279370 Thu, 12 Mar 2020 10:13:18 +0000 revor When I built my roof I put 170 mm or rock wool between rafters and then 100mm over clad the rafters with quinn therm taping the joints. That way the foam insulation was protected from most of the extreme heat.
There is a company that make special tape that fills the gap between the rafter and insulation but have no idea if it would cope with the shrinkage you describe.]]> Celotex shrinkage and warping https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279371#Comment_279371 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279371#Comment_279371 Thu, 12 Mar 2020 10:29:54 +0000 Pile-o-Stone Posted By: GreenPaddyYes, but more so with PUR boards. That's why they ought to be slightly undercut, and squirty foam all around edges.
Wouldn't the PIR/PUR board still contract over time and leave a gap between the board and the squirty foam?

I've limited experience with foam, but I've found it to be quite rigid and brittle once it's cured, so I can't imagine it moving with the PIR/PUR board to fill any shrinkage?]]> Celotex shrinkage and warping https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279372#Comment_279372 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279372#Comment_279372 Thu, 12 Mar 2020 11:07:43 +0000 Jonti Celotex shrinkage and warping https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279381#Comment_279381 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279381#Comment_279381 Thu, 12 Mar 2020 18:05:24 +0000 Peter_in_Hungary Posted By: JontiWould multi layers with staggered joints help to reduce the problem caused by shrinkage gaps?
Not if it is between the rafters or joists because you will still get gaps at the edges]]> Celotex shrinkage and warping https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279399#Comment_279399 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279399#Comment_279399 Fri, 13 Mar 2020 09:03:51 +0000 Jonti ]]> Celotex shrinkage and warping https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279407#Comment_279407 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279407#Comment_279407 Fri, 13 Mar 2020 10:13:14 +0000 fostertom Celotex shrinkage and warping https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279410#Comment_279410 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279410#Comment_279410 Fri, 13 Mar 2020 11:00:40 +0000 djh Posted By: fostertomAny suggestion this applies to EPS too?
I wrote: Not as far as I know. Providing you start with 'aged' sheets, not ones newly made. I think the conventional wisdom is they need three months of aging. No evidence of it in the stack of EPS in my garden.

And then I read: https://www.buildingscience.com/sites/default/files/migrate/pdf/PA_Foam_Shrinks_FHB.pdf

So now I'm as confused as you. Maybe he started with newly-minted sheets?]]> Celotex shrinkage and warping https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279412#Comment_279412 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16490&Focus=279412#Comment_279412 Fri, 13 Mar 2020 13:11:11 +0000 fostertom