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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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General: Embodied carbon, EWI, CWI, ASHP, Exposure zone 4

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    • CommentAuthorphiledge
    • CommentTimeJun 13th 2026
     
    With an 80mm cavity I'd have that filled with bonded EPS beads unless local installers say you've got excessive exposure. If you're worried about thermal bridging you can always cut out brick cavity closures around doors and windows, add some wall ties and fit insulated closures, prior to CWI. Tie in loft insulation to the top of the CWI and you've got a nice wrap around layer of insulation. You can add EWI later if you feel it's worth while
  2.  
    Seems like a lot of work for minimal gain on the bridges? Or in the grand scheme of things will it make much of a difference?
    • CommentAuthorphiledge
    • CommentTimeJun 14th 2026
     
    You mentioned concerns over cold bridging so binning the brick closures will get rid of them.

    I don't know how beneficial removing them would be from a total heat loss perspective but I do know that cold window reveals can cause condensation and subsequent mould. If you're gutting rooms anyway then the work/mess might not be a big deal but probably not worth it if removing the cold bridges is the only thing to do in an otherwise habitable/decorated room.
  4.  
    I could always, disc them out from the outside of the property I'm assuming that's the correct way to do it, but the windows would need to be removed in the first instance to obviously assess to see what is going on so far up there that I can't OK then seal up the inside. So any dust will be external only however, surely that, could potentially compromise the structural openings?
    • CommentAuthorphiledge
    • CommentTimeJun 15th 2026
     
    You'd cut them out from inside the window reveal. If you cut from the outside you'd end up with the outer leaf shorter than the inner leaf either side of the window opening.

    You would likely compromise the structure of the window opening so that's why you'd need to add wall ties if you removed the brick closure
  6.  
    Yeah I meant I'd have to remove the window, but could disc out from outside the room if that makes sense? Ie. Seal off the freshly decorated room as I'd imagine it will be quite messy doing so...
    • CommentAuthorphiledge
    • CommentTimeJun 15th 2026
     
    Ah, I undersrand now. If you're replacing windows anyway and likely need to rework the reveal, probably worth doing....I'd do it. Very dusty job so make sure you seal it up well from the room!!
  8.  
    just checking? Would I need a structural engineer to confirm the tie in for standard cavity wall. Or use ties drilled in such as the standard remedial wall tie replacement?
    • CommentAuthorphiledge
    • CommentTimeJun 15th 2026
     
    As a cavity wall is a standard construction the spacing of ties around openings should be in the building regs so no SE needed. I think for openings it's every 225mm vertically to tie in with block height, so every 3rd brick.

    If the brick closure has been formed by returning the inner leaf to meet the outer leaf with a vertical DPC so the inner and outer leaves are not brick bonded, then there should be ties around the opening already....should be!!
  10.  
    So this would only be worth doing if we were to keep the windows in the extraditing openings?

    No need to go to this extent if outing for EWI as well?
    • CommentAuthorphiledge
    • CommentTimeJun 18th 2026
     
    EWI will put some insulation over the brick closure if you dont replace the brick with an insulated closure but unlikely to get the full EWI depth depending on the detail around the windows. Whether it's worth it depends on how concerned you are about cold bridging or cool bridging if you add EWI.
  12.  
    That's the question I'm guessing how does one calculate the 'value' of one approach versus the other in terms of labour, efficiency gain, payback period and so on

    Basically is it worth it...
  13.  
    I'm going to look into this Cavipor system this week, see what the costings would be compared to standard EPS beads.

    I'm also wondering, is there ever any need to have DPM or closures on the cavities IF they are going to be filled? Surely they can be closed with blocks of EPS or just let the material that's going to fill the cavity simply fill against the windows?
    •  
      CommentAuthordjh
    • CommentTimeAug 22nd 2026
     
    Posted By: VictorianecoI'm also wondering, is there ever any need to have DPM or closures on the cavities IF they are going to be filled? Surely they can be closed with blocks of EPS or just let the material that's going to fill the cavity simply fill against the windows?
    Cavity closures need to be fireproof, which many insulation materials aren't. Depending on all surrounding detailing and the materials themselves they may also need to be protected from moisture/condensation.
  15.  
    Seems a lot of faff, labour and surplus materials then to cut out the brick ties to gain a nominal reduction in cold brushing?

    Any kind of calculation to be done in terms of cost v benefit of doing so?
  16.  
    Should I just pump the cavities with IWI for now and worry about any openings or further detailing at a later point?

    I mean if I need to recover concrete sills further on we can just fill the space with EPS blocks and expanding foam further down the line?

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