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Housing - New Build: Window details for brick clad SIP house

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    I'm a first time self builder and I'm struggling to get info on this detail. Does anyone know of, or can direct me to schematics on the best way to fit windows into a SIP built house with brick outer? If the window is fitted into the SIP reveal, how do I then bridge the cavity with the brick outer? Or should the window sit somewhere else in the SIP-brick cross section? Any experience? Window and SIP firms seem vague on this detail, and I'm struggling to find anything on the tinterweb.

    thanks
    James
    • CommentAuthortony
    • CommentTimeNov 9th 2011
     
    I would sit the windows behind the brickwork effectively in the cavity.

    <tonyshouse.info> /technical details/mitigation/window detail if you like
    • CommentAuthorCWatters
    • CommentTimeNov 9th 2011
     
    Perhaps take a look at manufacturers web sites for lintels/cavity trays (above the window to deflect water outwards) and cavity closures. They usually have fitting details showing window fixings.

    http://www.cavalok.com/why_cavity_closers.html

    Most builders use metal straps to hold the frame at the right depth in the opening but perhaps there are plasic ones for those worried about the thermal break...

    http://www.cavalok.com/downloads/Window%20Strap%20Fixing.pdf
    • CommentAuthorCWatters
    • CommentTimeNov 9th 2011 edited
     
    PS To some extent the depth depends on the size of the outer window sill (if you have one). The drip groove on the underside has to project beyond the brick skin. Very deep and very shallow sills can look a bit odd. See what sizes the window supplier/maker recommends.
    • CommentAuthorTimber
    • CommentTimeNov 10th 2011
     
    Don't forget your fire resisting cavity barriers around all openings!

    I can provide a bit more general info later.
    • CommentAuthorBen1974
    • CommentTimeNov 10th 2011
     
    We have a stone outer leaf to our SIP building and sat most of the windows so that they just closed off the cavity. The windows frames were 3" and sat about 1" into the stone work so bridging the cavity. The kingspan TEK panel site have some standard details which include detailing of cavity trays above the window and DPC under the window.

    We also lined the inside of the reveals with 12mm thermal break celotex after the windows had been fitted to try and improve the cold bridging at this location.

    I sympthise with you on the detail front. The SIP company that we dealt with didn't really help with the final detail and infact their designer seemed a little sketchy on it when pressed. I think this partly comes down to the division of responsibility for design between the SIP supplier and the main architect.

    As for fire resisting cavity barriers try a specialist supplier but be aware that even they talk about the problems that they can create by trapping water/moisture against the timber frame. I believe if you use a wooden window with a frame of sufficient thickness this will count anyway.
    • CommentAuthorTimber
    • CommentTimeNov 10th 2011 edited
     
    The best bet for thermal bridging is to place the window entirely within the SIP. Obviously for asthetic reasons, pushing the window out to the stone work is normal proceedure.

    In that case, the best form of cavity barrier to use is a 38 mm thick timber batten wide enough to close the cavity. This is protected from the stone with a dpc that is lapped into the SIP window opening and lapped with and sealed to the vapour control layer. Then install the window and seal the winow to the timber batten and SIP reveal. This ensures air tightness around the window junction and moisture tightness of the SIP envelope. Ideally, do as the scots do, and install the window in a check reveal setup.

    Metal strapping can be used to hold the windows back to the SIP, or fix to the timber batten.

    If you want to improve themal bridging, thin insulation board to the reveal, as mentioned by Ben will help.
    • CommentAuthorTimber
    • CommentTimeNov 10th 2011
     
    To add to the above, if over a single storey, consider differential movement on the upper storey windows. There shouldn't be much, but it depends on the exact construction. Timber ground floors increase differential movement.
  9.  
    Many thanks for the comments. I'll relay to our suppliers and update this post, when we've settled on a solution.
    • CommentAuthorborpin
    • CommentTimeNov 20th 2011 edited
     
    Posted By: CWattersPerhaps take a look at manufacturers web sites for lintels/cavity trays (above the window to deflect water outwards) and cavity closures. They usually have fitting details showing window fixings. http://www.cavalok.com/why_cavity_closers.html
    Bit OT but there was discussion elsewhere (can't find it right now) about fitting windows in EWI using a plywood box. Could these cavity closers be used instead (even though there may be no cavity)? Would there be an advantage in terms of thermal bridging? Assuming the internal structure was TF or Block, you would need straps back to the structure to secure the window frame but this seems to take the weight of the frame (or else I have completely mis-read this product). :sad:
  11.  
    You cannot fix into plastic cavity closers like the Cavalok. You need to fix the window frames to a plywood box or via steel straps to something structural, e.g. outer leaf, inner leaf, timber frame or SIP.

    David
    • CommentAuthorCWatters
    • CommentTimeNov 21st 2011 edited
     
    Posted By: borpin
    Posted By: CWattersPerhaps take a look at manufacturers web sites for lintels/cavity trays (above the window to deflect water outwards) and cavity closures. They usually have fitting details showing window fixings. http://www.cavalok.com/why_cavity_closers.html
    Bit OT but there was discussion elsewhere (can't find it right now) about fitting windows in EWI using a plywood box. Could these cavity closers be used instead (even though there may be no cavity)? Would there be an advantage in terms of thermal bridging? Assuming the internal structure was TF or Block, you would need straps back to the structure to secure the window frame but this seems to take the weight of the frame (or else I have completely mis-read this product).:sad:" alt=":sad:" src="https:///forum114/extensions/Vanillacons/smilies/standard/sad.gif" complete="complete" >


    No as the rest of my post said you normally use these or similar metal straps at many points around the frame to fix back to the inner leaf.

    http://www.cavalok.com/downloads/Window%20Strap%20Fixing.pdf
    • CommentAuthorborpin
    • CommentTimeNov 21st 2011 edited
     
    Posted By: davidfreeboroughYou cannot fix into plastic cavity closers like the Cavalok. You need to fix the window frames to a plywood box or via steel straps to something structural, e.g. outer leaf, inner leaf, timber frame or SIP.
    Just been and looked at some windows today and that is what they do (use straps). They also tape internally and use expanding foam round the frame with a soft foam (old type draft excluder) on the outside edge of the gap they foam (not sure that makes sense, should have taken a photo). How much thermal bridge do the straps give?
    On the basis of a TF with EWI of EPS, the alternative, as I see it, is a plywood box, deep enough to be secured to the inner frame, with possibly a 50x50 'band' around the plywood box where the window will be mounted central to the insulation. Box fixed to fram, windoe fixed into the 50x50 band. Does that sound like a good detail?
  14.  
    I guess the soft foam is something like Compriband:

    http://www.tremco-illbruck.co.uk/products/00816_index.html

    This gives a better long term seal than a thin bead of silicone sealant because its more tolerant of relative movement between frame & structure. However, it has got to be used in compression, so its not suited to all situations.

    The straps will give a certain amount of thermal bridging, but this can be limited by keeping the cross sectional area to a minumum (no big nail plates) & using stainless steel. The key things are to keep the window frame in line with the wall insulation & to minimise the amount of structure which bridges across around the window.

    I would position the window such that it is entirely surrounded by insulation, terminate the internal plywood box flush with the inner face of the window frame, fix the frame to the internal plywood box with short straps & seal the window frame to the internal plywood box & the external weatherproof layer.

    David
    • CommentAuthorborpin
    • CommentTimeNov 22nd 2011
     
    Posted By: davidfreeboroughI would position the window such that it is entirely surrounded by insulation, terminate the internal plywood box flush with the inner face of the window frame, fix the frame to the internal plywood box with short straps & seal the window frame to the internal plywood box & the external weatherproof layer.
    Thanks David. If you terminate the Plywood at the inner face of the frame does this mean the window is simply held by the straps? What then is the purpose of the plywood box? As a cavity closer? If so, the plan is to have EPS directly on the TF structure (warm stud). I have difficulty believing that the straps alone could support a 1000x1000 3G, 92mm profile (heavy) window or have I missed something?
    Brian
  16.  
    The purpose of the plywood box is to carry the weight of the window back to the structural timber frame, continue the air barrier around the reveal & provide something to seal to at the inner face of the window frame.

    There are straps specifically designed for the job & it's common practice to use these to fix windows in a 100-150mm wall cavity to the inner leaf. Here the straps only need to transfer the load a few 10s of mm, so I don't think they're going to move much.

    David
    • CommentAuthorCWatters
    • CommentTimeNov 22nd 2011
     
    The straps are used at the sides as well as the top and bottom. Those at the sides are loaded in the "strong direction" if you understand that expression.

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