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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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    • CommentAuthorShevek
    • CommentTimeJun 19th 2018 edited
     
    The three approaches I know of for supporting windows out in the insulation zone of EWI is:

    1. Plywood box fixed to masonry/timber structure
    2. Metal brackets/lugs fixed to masonry/timber structure
    3. Structural insulation (box, bottom rail/block support) fixed to masonry/timber structure (e.g. Compacfoam)

    What are the pros and cons of each approach and is there any consensus here on the best approach these days?
    • CommentAuthorgravelld
    • CommentTimeJun 20th 2018
     
    4. Beefier timber blocks e.g. http://www.fourwalls-uk.com/blog/2013/06/13/readers-request-more-information-on-window-fitting/

    Also 3 and 2 can be combined I think, insulation at bottom, brackets on side.

    Some more reading, sorry, unstructured:

    https://forum.buildhub.org.uk/blogs/entry/245-fitting-of-new-windows-in-ewi-layer-using-ewi-brackets/

    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15490

    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15179

    I would say the advantages/disadvantages are:

    1) Familiar materials
    2) Greater flexibility of window sizing, maybe less work
    3) Best performing, but most expensive (Compacfoam specifically)
    • CommentAuthortony
    • CommentTimeJun 20th 2018
     
    I would add that it is best to support the weight of the window on a steel or stainless rod drilled into the relevant mortar bed immediately below the reveal external masonry and for larger windows a centre support is important too.

    Consider air tightness of everything you do
    •  
      CommentAuthorfostertom
    • CommentTimeJun 20th 2018
     
    Also consider the huge conductivity (50W/mK) of even a small cross section of steel, direct to the inside, just where you've been to great lengths to minimise cold bridging around the perimeter.

    You can have 385x as much cross sectional area of OSB (0.13W/mK) in same location (but continuous instead of intermittent) before it equals the thermal bridging of a steel bracket solution.
    •  
      CommentAuthordjh
    • CommentTimeJun 20th 2018
     
    Posted By: fostertomAlso consider the huge conductivity (50W/mK) of even a small cross section of steel

    Very true, but note that's a figure for mild steel. Stainless has a conductivity about a third of that.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 20th 2018
     
    OK but still 128x. And how many of us will be using stainless L-brackets, when galv ones cost less than a quid each?
    •  
      CommentAuthordjh
    • CommentTimeJun 20th 2018
     
    Posted By: fostertomhow many of us will be using stainless L-brackets, when galv ones cost less than a quid each

    Those that care about thermal bridging?
    • CommentAuthorbhommels
    • CommentTimeJun 21st 2018
     
    My £0.02: I have used 2), with L shaped straps bolted to the inner leaf. Works very well, although the airtight layer is a bit of a faff to get around the brackets neatly. There 1) would be better, but a lot more work making it all square & plumb as well as strong enough to support a large triple glazed window unit. 3) for doors or very, very heavy window units.
    • CommentAuthorgyrogear
    • CommentTimeJun 21st 2018
     
    In my case the solution was a hybrid of number (2) "metal brackets/lugs fixed to masonry/timber structure" (for the uprights) , and a "fudge" for the bottom rail, namely seating it on the concrete floor slab.

    The installation is a corner glazing system and the weights are formidable:
    frontal glass = dual lift-and-slide sashes, span 2.8 x 1.4 m high; plus corner tilt-and-turn, plus sloping roof glass; plus guardrail and safety glazing...

    Before and after photos.

    gg
      After.jpg
    • CommentAuthorgoodevans
    • CommentTimeJun 21st 2018
     
    I'm going for option 4 - Beefier timber blocks - line the inside of the reveal with a AT membrane to be extended into the wet plaster with a seal between the membrane and the window frame in place before the plastering.

    The timber will allow the frame to be packed and squared against something solid - main risk is the rotting of the timber sub frame.
    • CommentAuthortony
    • CommentTimeJun 21st 2018 edited
     
    I would say that is a certainty not a risk
    • CommentAuthorSilky
    • CommentTimeJun 23rd 2018
     
    +1 on this topic,

    I'm trying to source Compacfoam in Germany but may now go to the 'Beefier' solution. Thought on this, Western red cedar is a better insulator than the other common woods ( 0.09 ). Thermally modified wood insulates better than non-TMT (I've read 20% better). Maybe TMT Red Cedar could be 0.07? When considering the overall build-up I can see the advantages of Compacfoam becoming negligible, particularly if the wood is not too bad an insulator and then covered with insulation. After all, the windows itself is always going to be the elephant in the room when it comes to heat loss.
    •  
      CommentAuthordjh
    • CommentTimeJun 23rd 2018
     
    WRC is also more durable than generic softwood. Probably more expensive too, though!
    • CommentAuthoradam_w
    • CommentTimeJun 27th 2018
     
    Sorry to jump in on your thread Shevek, but which one of these methods would be best suited for a door as well?

    Thanks,

    Adam
    • CommentAuthortony
    • CommentTimeJun 27th 2018
     
    What type of threshold does the door have?
    • CommentAuthoradam_w
    • CommentTimeJun 27th 2018 edited
     
    Posted By: tonyWhat type of threshold does the door have?


    Tony,

    I haven't ordered the door yet but it'll just be a standard UPVC variant. If however you mean the doorway itself, its 100mm block with 100mm external EPS rendered.

    thanks,

    Adam
    • CommentAuthortony
    • CommentTimeJun 27th 2018
     
    No, you need to think what the threshold will sit on, standard plastic thresholds are prone to damage and planning/building regs often require level thresholds.
    • CommentAuthoradam_w
    • CommentTimeJun 28th 2018
     
    Posted By: tonyNo, you need to think what the threshold will sit on, standard plastic thresholds are prone to damage and planning/building regs often require level thresholds.


    Tony,

    this door is as the back of my garage on to the patio so the floor levels either side are about 100mm under DPC. The low threshold option that comes with the door is about 15mm.

    Many thanks,

    Adam
    • CommentAuthorborpin
    • CommentTimeJul 5th 2018
     
    If a timber frame then I'd always use the box method. You do though, need to decide that before the structure is specified and the windows ordered :)
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