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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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    • CommentAuthorgravelld
    • CommentTimeNov 1st 2018
    I need to make a hole for a new sliding door, about 4.5m. Cavity wall.

    I assumed this was just with two steel beams (RSJs) under each leaf. But if I search for "cavity wall lintel" I get results like these: https://iglintels.com/lintels/standard-lintels/100mm-inner-leaf-100mm-outer-leaf-lintels/

    Are those just new build only or can they be used in a refurb? I couldn't find anything related to this at the above site.

    Any best practice details for retrofit lintels in a cavity wall? Couldn't find much. No chance of EWI or IWI.
    • CommentAuthortony
    • CommentTimeNov 1st 2018
    It is best to build those lintels in, sometimes they say build three courses of bricks on them

    It will be tricky to find one for a narrow enough cavity and for a 4.5m opening you ought to be getting an engineers design I think
    • CommentTimeNov 1st 2018
    gravelld asked: 'Are those just new build only or can they be used in a refurb? I couldn't find anything related to this at the above site'.

    A well-known brand for thermally broken lintels is Catnic - https://catnic.com/products/lintels/thermally-broken-lintels/overview - but when I searched I see that the company you mentioned also do them - https://iglintels.com/hi-therm-lintel/ I expect they would be better than the products you mentioned.

    As far as whether you can retrofit them, I would suggest asking their technical department. I can't immediately think of a reason why not, but then I'm not qualified.
    • CommentAuthorphiledge
    • CommentTimeNov 1st 2018
    In the past Catnic had a design service where you provide the wall construction detail and the load type over the opening(plain wall, floor, roof etc) and they will specify a lintel for you. I assume they still offer that service and IG do the same. From the link you sent, IG go well beyond a 4.5 metre opening.

    The manufacturer will confirm, but the lintels you linked to are for masonary construction and so long as the detailing is corrrect, I cant see any reason why they shouldnt be used in retrofit as well as new build.
    • CommentAuthorgravelld
    • CommentTimeNov 2nd 2018
    Thanks everyone, that's very clear.
    • CommentAuthorgoodevans
    • CommentTimeNov 2nd 2018 edited
    That is a big hole - what is above it - it makes a difference.

    Flat roof with joists running parallel to the hole - no problem, no load.

    Gable end with block/brick - doable with universal beams - may be able to have one beam for each skin. The load is the triangle of wall above the beam not supported by corbling - but an SE is req.

    Worst case is roof eaves or first floor joist supported just above the opening - in this case you have the roof dead load and the not insignificant snow loads etc or the first floor dead loads and live load.

    Until you/your engineer know the load you have to support there is no way to answer the question.
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