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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.

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    • CommentAuthordsewell
    • CommentTimeJun 20th 2017

    Does anybody know of XPS boards that are "certified" for use in cavity walls below DPC? We were planning on using 275mm Polyfoam XPS Floorboard around the perimiter of a 300mm cavity, but the boards are not "certified" for use in walls and come in 600mm sheets not 450mm.

    Consequently, our warranty company has informed us we can not cut the floorboards for use in a cavity wall. (Grrr :angry:)

    So, have been frantically searching for an XPS board we CAN use in a cavity (with certificates) but it looks like PIR has taken over. (We preferred the idea of XPS vs PIR as we understand this would perform better below DPC where there could be moisture.)

    Does anybody know of an XPS manufacturer that supplies boards specifically for use in cavities?

    • CommentTimeJun 21st 2017
    A search for XPS cavity insulation seems to indicate that all the major firms do. I would suggest contacting them or one of the specialist insulation suppliers.

    Why not use EPS? Jabfill HP as just one example appears to be designed for exactly what you want.
    • CommentAuthordsewell
    • CommentTimeJun 21st 2017
    Thank you, yes we have looked at Jabfill HP we just need to confirm how to increase the depth as we have 300mm cavities and this comes in 75, 100 or 150 depths but can't be doubled up due to the drip details.

    One option we are looking at is Jabfill as the outermost insulation layer with other EPS/XPS behind if.
    • CommentAuthordsewell
    • CommentTimeJun 27th 2017
    So, Building Control were ok with 100mm Jabfill HP as the outermost layer with 200mm XPS behind. Just needed to add DPM at the corners.

    Thank you for helping with this one. And, hopefully by confirming this was ok with BC it may help others.
    Any reason to use 200mm XPS rather than 200mm EPS behind the Jabfill?
    • CommentAuthordsewell
    • CommentTimeJun 28th 2017
    Honestly, no specific reason for XPS vs EPS.

    If there were one main reason it would be that we are using XPS under the slab so we are already buying loads of it and offcuts from the floor can go in the wall and vice-versa.

    Also, generally XPS is supposed to be better than EPS in the ground. That's probably a big 'generally'. And, I guess for historic / conveneience reasons - we choose XPS originally its what we put in the PHPP, the spec and all the drawings.
    • CommentTimeJun 28th 2017 edited
    Posted By: dsewellAlso, generally XPS is supposed to be better than EPS in the ground.

    Only if you read XPS websites. If you read EPS websites, they say EPS is better than XPS in the ground. In short, I haven't found any definitive evidence anywhere.
    Apart from the cost issue of XPS vs. EPS have a read of -
    • CommentTimeJun 29th 2017
    Yes, that's the kind of thing the EPS industry publishes. It's notable that they don't provide a reference to the claimed independent test results and have refused to provide copies. Also that the document says "The information contained herein is provided without any express or implied warranty as to its truthfulness or accuracy." It does tend to indicate the importance of proper drainage though. Here's a rebuttal by one of the XPS boys:


    I haven't found any definitive evidence anywhere. Personally I'm very happy to be living on top of a big bunch of EPS.
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