Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)


Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!

powered by Surfing Waves

Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.

    I have recently started some renovation work on my property and removed the plaster board revealing Celotex insulation fitted between the rafters. To my horror I have found the Celotex PIR board to be shrunk and warped ! This explains why my property has been so cold ! It has been fitted for approximately 17 years, but I would not expect this from a product that is surly meant to last the lifetime of the building ?
    Has anyone else experienced this ?
    • CommentAuthorGreenPaddy
    • CommentTimeMar 12th 2020
    Yes, but more so with PUR boards. That's why they ought to be slightly undercut, and squirty foam all around edges. It's even better looking under "well insulated" suspended floors, to find a nice layer of kingspan covering the solum, having dropped out from between the joists. Meets all the regs on paper, but a few years down the line, it's back to living in a timber shed.
    • CommentAuthorJeff B
    • CommentTimeMar 12th 2020
    Makes me wonder what the state of the insulation in the skeilings of my dormer bungalow must be like as I cannot really see what is happening above them. Just as well that I have done IWI on them then!
    • CommentAuthorrevor
    • CommentTimeMar 12th 2020
    Yes I have commented on this a few months ago but cannot remember what thread it was under. I had some delivered warped and with concave edges just over 12 months ago they got sent back.They were due for the floor. Seems they had been exposed to the sun in the builders merchant yard. I was made aware of this problem a few years back when a builder friend went to extend a roof he had build some 10 yrs earlier. He found the same result as you
    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.
    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?
    • CommentAuthorJonti
    • CommentTimeMar 12th 2020
    Would multi layers with staggered joints help to reduce the problem caused by shrinkage gaps?
    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
    • CommentAuthorJonti
    • CommentTimeMar 13th 2020
    So the next question would be is the shrinkage a one time thing that stops after a certain point? If so should only age cured be installed :wink:
    • CommentTimeMar 13th 2020
    Any suggestion this applies to EPS too? as EPS is not a monolithic lump of foam, but conglomerated beads of same. And does this in fact affect all the foamed insulations - PIR, PUR, XPS?
    • CommentTimeMar 13th 2020
    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?
    • CommentTimeMar 13th 2020
    Great article, will study. I should think, back then (a 2012 revisit of a project 16yrs previous), 'aged' was an unknown concept.
Add your comments

    Username Password
  • Format comments as
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   

© Green Building Press