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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.

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    • CommentAuthorkebl2825
    • CommentTimeFeb 24th 2021
    I'm planning insulation for ground floor suspended timber floor, Victorian end terrace.
    Most of the ground floor has approx 600mm void below the joists, with front of house approx 250mm deep below joists (below a bay window area). 100mm deep joists (running parallel to front wall), sat on frequent sleeper walls running front to back. Sleeper walls have a dpm across top then plywood packers/shims under joists to level.

    From what I have read so far my strategy is:
    100mm mineral wool between joists (rigid PIR in the shallower area).
    200mm total EPS board below joists (with less/none below in the shallower area). Possibly in 2 layers so I can stagger the joins, mechanically fixing the first layer through to joists.
    Lime parge coat external walls (level off, and air-tightness), at least 100mm below joists.

    At the perimeters the advice seems to be rigid boards foamed in, and the external perimeters are relatively more important than the middle of the floor. I'll make sure to not block any airbricks, and give them a path through to below the new insulation.
    How far down the inside of external walls should perimeter insulation boards go - down to the ground below, or even dug out a bit so goes below ground, or just to roughly meet the depth of the underfloor insulation?
    And, same question, but for the inner walls, sleeper walls, and party wall.

    What type of expanding foam should I be considering?

    And - forgive my ignorance - how is the 'foaming in' of a rigid board actually done? What are the dos and don'ts I should keep in mind?
    I haven't (yet) been able to find a guide that doesn't gloss over this and the perimeters seem an important detail to get right.
    Would I friction fit the board into place then just foam every exposed join/edge from my side?
    I would expect it is important to not have significant air gaps left behind any vertical perimeter boards - so I think I wouldn't want the foam expanding itself behind them and forcing them away from the wall which surely could happen if I don't at least brace the boards till the expansion stops.
    • CommentAuthortony
    • CommentTimeFeb 24th 2021
    I like eps and it works well, condensation can form on the underside and safely drip away

    Never touch walls with quilt - so use eps between quilt and wall.

    you can use fixing foam as opposed to expanding foam and I would spray backs of sheets then press to wall a ribbon top and bottom and at the ends

    Happy to talk
    • CommentAuthorjms452
    • CommentTimeFeb 24th 2021
    Posted By: tonyNever touch walls with quilt

    Why's that - is it avoid breach of bellow dpc walls to joists?
    • CommentAuthorkebl2825
    • CommentTimeFeb 24th 2021
    Okay cheers Tony that makes sense so I'd basically form a continuous bead of foam, intentionally, rather than trying to work against it. I can see there are some low/minimal expansion plasterboard fixing foams - I was being too specific in my searches missing the obvious.

    Is there a best practice for how far the perimeter insulation should go down the wall face? If at all?
    Does it matter if EPS board+foam on a wall face bridges over dpm?
    • CommentAuthortony
    • CommentTimeFeb 24th 2021
    If it gets wet or damp it is ugly, goes soggy can slump, and hold water near wood
    • CommentAuthorSimonD
    • CommentTimeFeb 25th 2021 edited
    Posted By: kebl2825
    Is there a best practice for how far the perimeter insulation should go down the wall face? If at all?
    Does it matter if EPS board+foam on a wall face bridges over dpm?

    Technically speaking, wall insulation should extend 200mm below the top of the joists. I don't think it's a good idea to bridge the dpc. I have installed floor insulation with a strip of eps insulation below the joists and cut away the topd corner of the eps at dpc to avoid any potential bridge.

    I attached a photo of a recent installation where I've gone overboard and extended the plinth insulation 200mm below the bottom of the joists (145mm joists) - this is partly because I've got ewi going on and external plinth insulation extending to just below ground level below dpc.

    (oh, and for some reason the image is being turned upside down by the forum software, so sorry if you have to stand on your head to make sense of it)
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