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    • CommentAuthorgravelld
    • CommentTimeJan 8th 2018 edited
     
    Here's my starting point for a windows detail. As with the previous eaves detail thread, the current building is:

    - (Mostly) cavity wall, insulated
    - Cold loft, insulated to ~U0.1
    - Rendered
    - Air tightness of a colander

    The planned retrofit includes EWI and replacement of windows.

    In this detail I am assuming much of the technical detail will be provided by the manufacturer.

    I have sought to position the window in the insulation layer and will require a detail from the manufacturer to this end. In this detail I have preferred the window-subframe approach, rather than using brackets, Compacfoam, plywood boxes etc. This is because:

    - Timber is cheaper than compacfoam
    - I don't quite need the performance Compacfoam provides
    - Builders are more familiar with it and its one less thing to explain!
    - More leniency on window size - I could oversize (I think) to get more glazing area, plus less worry about the sizing being mm-accurate.

    Just wondered what others thought of this, anything obvious missing?

    Notice the window is larger than the opening. I thought this is a key advantage of this approach (see last point above). However, is it actually impossible - are extra fastenings required into the internal reveal which means we cannot offset like this?

    I added the PU foam bit to provide more of a thermal break, maybe it's not needed.

    References:
    - http://www.fourwalls-uk.com/blog/2013/06/13/readers-request-more-information-on-window-fitting/
      basic_window.JPG
    •  
      CommentAuthordjh
    • CommentTimeJan 8th 2018
     
    Posted By: gravelldIn this detail I am assuming much of the technical detail will be provided by the manufacturer.

    I have sought to position the window in the insulation layer and will require a detail from the manufacturer to this end.

    You mean the window manufacturer? I think you're very unlikely to get any such detail from them. They're not in the business of designing your house or of assuming design risk on your project.

    Why Tescon No 1? Why not the same Contega Solido Exo as elsewhere, or Tescon Vana?

    I wouldn't use PU foam where you show it. Firstly, I would extend the window board to meet the window frame otherwise it will look very messy after a few years. Secondly, underneath the window board I would either use a compressible gasket (Combriband maybe?) or a permanently flexible foam (which would either need an airtightness guarantee or a vapour tape connection as well)

    How is the window frame attached to the subframe? And when.

    What exact model of window sill is it and how is it attached to the frame and to the insulation underneath?
    • CommentAuthortony
    • CommentTimeJan 8th 2018
     
    You MUST have a render drip bead a rod the head of the reveal.

    I like overlapping the insulation onto the frames and fitting the frame outside the blockwork

    I would use an insulated reveal lining inside including under the windowdoard at least across the outside skin and cavity.

    I would like to see where the air barrier is and how it joined to other elements.
    • CommentAuthorgravelld
    • CommentTimeJan 9th 2018
     
    Posted By: djh
    Posted By: gravelldIn this detail I am assuming much of the technical detail will be provided by the manufacturer.

    I have sought to position the window in the insulation layer and will require a detail from the manufacturer to this end.

    You mean the window manufacturer? I think you're very unlikely to get any such detail from them. They're not in the business of designing your house or of assuming design risk on your project.

    Yes, that's what I meant. Bugger, I thought they'd provide this if asked (EWI systems technical staff seem to have a lot of details hidden on their computers that they provide when you ask for them, and aren't on their website).

    Posted By: djhWhy Tescon No 1? Why not the same Contega Solido Exo as elsewhere, or Tescon Vana?

    I think Vana might be better actually, because No. 1 is just wood to wood correct? The finish on the window may be alu, so that wouldn't work and I believe Vana permits alu? I didn't double check that.

    Posted By: djh
    I wouldn't use PU foam where you show it. Firstly, I would extend the window board to meet the window frame otherwise it will look very messy after a few years. Secondly, underneath the window board I would either use a compressible gasket (Combriband maybe?) or a permanently flexible foam (which would either need an airtightness guarantee or a vapour tape connection as well)

    Compriband is just a tape right - it's only a cm or two wide at best - what sort of coverage do you mean?

    Posted By: djh
    How is the window frame attached to the subframe? And when.

    I forgot to cite my references. This basically copies http://www.fourwalls-uk.com/blog/2013/06/13/readers-request-more-information-on-window-fitting/ although with a deeper subframe and offsetting the frame to allow for more glazing.

    As far as I can see the window is attached to the subframe using whatever approach would see the window attached to any other opening, PLUS nail plates are used - and this is what I'm worried about with offsetting the frame - the nail plates couldn't be used if the sub frame is not flush with the opening, correct?

    Posted By: djh
    What exact model of window sill is it and how is it attached to the frame and to the insulation underneath?

    I assumed this was window manufacturer supplied and, again, the installation detail would be supplied by them.
    • CommentAuthorgravelld
    • CommentTimeJan 9th 2018
     
    Posted By: tonyYou MUST have a render drip bead a rod the head of the reveal.

    I like overlapping the insulation onto the frames and fitting the frame outside the blockwork

    I would use an insulated reveal lining inside including under the windowdoard at least across the outside skin and cavity.

    I would like to see where the air barrier is and how it joined to other elements.
    Thanks Tony. I forgot to say that the tape goes onto the existing external render layer. Something to add; that's the air barrier.

    Why is it important to insulate the internal reveals? Note this may need to be done later due to budget.
    • CommentAuthortony
    • CommentTimeJan 9th 2018
     
    You are probably ok without but there is a slight thermal bridge, I would work about air infiltration into the cavity causing cold spots in the reveal.
    • CommentAuthorgravelld
    • CommentTimeJan 9th 2018
     
    Hopefully there won't be because the air barrier is outside of the cavity... I see your point about the internal reveals, do you mean because the external leaf is connecting to the ground (we don't have floor insulation, instead we will install plinth insulation).
    • CommentAuthorgravelld
    • CommentTimeJan 9th 2018 edited
     
    New version
    - Added drip bead to head
    - Removed pu foam and reduced size of subframe
    - Added internal reveal insulation
    - Changed tapes, added ref to existing render based AT layer

    What should I do about any existing DPC which exists in the cavity? Or indeed, any existing weep holes? Should I confirm they should be simply insulated over and not replaced?

    I don't need AT internally from window to reveal, correct? djh it looked like you were suggesting this?
      window_detail.JPG
    • CommentAuthortony
    • CommentTimeJan 9th 2018
     
    What is the window sub frame for? do you mean 80mm x 70mm for it -- I used angle brackets and diagonal screws straight through the window frame with double set of threads(one near the head so as not to distort the frame) = more insulation, less bridging, nothing to go rotten.
    • CommentAuthorgravelld
    • CommentTimeJan 10th 2018 edited
     
    As above:

    - Timber is cheaper than compacfoam
    - I don't quite need the performance Compacfoam provides
    - Builders are more familiar with it and its one less thing to explain!
    - More leniency on window size - I could oversize (I think) to get more glazing area, plus less worry about the sizing being mm-accurate.

    Although it sounds like you didn't even use Compacfoam. Is there a limit to sizing when using _only_ brackets?

    Do you have a detail for your approach? Can't see anything on http://tonyshouse.readinguk.org
    • CommentAuthortony
    • CommentTimeJan 10th 2018 edited
     
    I can’t draw very well

    http://tonyshouse.readinguk.org/tony205.jpg

    A bit of wood under a door frame will definitely go rotten, it will probably set the bottom block rolling and wriggling about too.
    • CommentAuthorMarkyP
    • CommentTimeJan 10th 2018
     
    are the window frames sufficient to allow the oversizing, the reveal insulation and the window board without encroaching onto the glazed area?

    why oversize? is it significantly thermally better than just fully outboarding the window?

    I would outboard using angle brackets to the side of the frame and face of the outer skin. I partially outboarded my windows in my EWI in this manner, see my EWI installation thread. No reason this approach could not be used to fully outboard IMO.
    •  
      CommentAuthordjh
    • CommentTimeJan 10th 2018
     
    Posted By: gravelldI don't need AT internally from window to reveal, correct? djh it looked like you were suggesting this?

    You do need airtightness internally, indeed vapour tightness. Otherwise you will have the potential for air and vapour movement within the depth of the wall.
    • CommentAuthorgravelld
    • CommentTimeJan 10th 2018
     
    Posted By: tonyI can’t draw very well

    http://tonyshouse.readinguk.org/tony205.jpg" rel="nofollow" >http://tonyshouse.readinguk.org/tony205.jpg

    A bit of wood under a door frame will definitely go rotten, it will probably set the bottom block rolling and wriggling about too.
    Thanks - can't see the screws and brackets though?

    For the doors I was thinking the Compacfoam route but still to do some research.
    • CommentAuthorgravelld
    • CommentTimeJan 10th 2018 edited
     
    Posted By: MarkyPare the window frames sufficient to allow the oversizing, the reveal insulation and the window board without encroaching onto the glazed area?

    why oversize? is it significantly thermally better than just fully outboarding the window?

    Not sure I understand - the window is fully outboarded isn't it? Also, I don't understand what you mean by "sufficient".

    I wanted to oversize, or have the option of doing so, in case the frames in the procured windows are much larger meaning we have less glazing than currently; I think such a reduction may be looked on as sub optimal by other "stakeholders" especially given I *have* got the go ahead to significantly reduce N facing glazing. Like with some other aspects, the requirement to oversize will only be needed depending on the final chosen windows.

    Posted By: MarkyPI would outboard using angle brackets to the side of the frame and face of the outer skin. I partially outboarded my windows in my EWI in this manner, see my EWI installation thread. No reason this approach could not be used to fully outboard IMO.
    Ok, another vote for angle brackets, I'm listening...

    Is this what you mean: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15355#Comment_262583 ?

    Are you basically saying to flip the brackets so they are going outside rather than inside? Any maybe not have those "packers"?

    Is there a wide range of brackets so we could choose one to fit the window fastenings?

    Could the brackets be placed further apart in case the window was delivered too large (I know I sound a bit obsessed with this but just wondered).

    How would the bracket approach work when windows finish flush with the top of a wall in the eaves? Oh - I guess just flat brackets rather than L shapes (facepalm).
    • CommentAuthorgravelld
    • CommentTimeJan 10th 2018
     
    Posted By: djh
    Posted By: gravelldI don't need AT internally from window to reveal, correct? djh it looked like you were suggesting this?

    You do need airtightness internally, indeed vapour tightness. Otherwise you will have the potential for air and vapour movement within the depth of the wall.
    Ok. Back to the compriband suggestion then - given it's a tape rather than a panel how are you saying to fit this?

    If it's just vapour (or air) tightness required why not just fit internal tape from window to internal reveal? Is it also important to cover the top of the cavity wall - in which case could a membrane be used, taped?

    Thing is, even if this is done remember there are doubtless a crap load of other inaccessible places across the house there will already be cracks and so on.
    • CommentAuthorMarkyP
    • CommentTimeJan 11th 2018 edited
     
    on the outboarding I was just wondering the rationale for the oversizing. Regarding the frame size, I mean the width of the frame, that is the distance from the outside edge of the frame to the inside edge, as viewed face on to the window. Perhaps you drawing isn't scaled but it appears you have perhaps an oversize of 25mm (straight away you've used up a chunk of frame width), then some insulation (maybe 25mm), window board (maybe another 20mm). So with all that, I wonder if you will find your window board is sitting higher than the glass, or at least higher than the inside edge of the frame and encroaching into the sash frame if there is one.

    It sounds like you are worried about sizing the windows accurately. I had a rough cast render on the existing walls so chipped bits away in the reveals to expose the frame edges and blocks and was able to measure the existing windows and see the sort of fitting tolerance this left me. In a few cases the existing windows were a bit tight, so I adjusted my measurement accordingly. In one case we mixed a window up during installation and ended up with one a shade too large for a reveal, so it was out with the reciprocating saw and masonry blade, and we made the reveal 20mm wider- easy enough to modify openings when you have blockwork which will be covered later. If you can, I would work to get your windows sized accurately. I've been through it, as have others here, windows are one of most tiresome aspects of a project! I spent hours and hours measuring, re-measuring and reading over supplier details

    brackets - yes, that's the pic I meant (thanks, lazy of me not to link it). In your case I would flip the brackets around 180 degrees but otherwise same approach. The packers will be needed unless your walls are perfectly flat and plumb and you have fixed your brackets exactly in the same plane.

    if a window finishes flush at the top I would, as you say, use flat plate or section of cut up wall strapping. taken back to something you can get a fix through into like a lintel
    • CommentAuthorgravelld
    • CommentTimeJan 11th 2018
     
    Great, thanks for that. Right now I considered the oversizing dimensions dependent on the window we went for. The final detail would have to have the correct window frame sizes drawn and labelled.

    Perhaps I should drop my worry about sizing the windows accurately. We have twenty-two openings to account for and I want to lower disruption to a minimum, so don't fancy hacking away the wall. The biggest question to me was to ensure the openings worked, e.g. windows opened fully (not decided about inward/outward opening yet for upstairs; outward for downstairs probably).

    I just thought the bracket approach would give some leeway.

    There are also small advantages in the energy modelling, potentially, for solar gain (although I'm being careful with the overheating in certain rooms).

    One idea: drill the external reveal until I hit block, measure it and add that to the exposed frame size? Then fill again.
    • CommentAuthorborpin
    • CommentTimeJan 11th 2018
     
    I realise you ruled it out, but I'm a fan of the window box method. Put a Ply box round the frame, outside edge of box flush with outside of window and box extends inwards to the inner wall. Thin line of sealant between box and frame as it is fitted. Then fix through the box into the inner/outerleaf with enough of a gap to be able to properly fom gap. Flexifoam between box and inner & outer leafs. Fill cavity with foam before you start and trim off as best as possible. If you want a larger glazed area cut window opening out slightly.

    Make sure you can still open the windows with your method. Overlapping that much I'd suggest could prevent them opening (if inward).
    • CommentAuthorgravelld
    • CommentTimeJan 11th 2018
     
    Thanks, can you describe what you see as the advantages? E.g. consider performance, ease of install, cost...
    • CommentAuthorborpin
    • CommentTimeJan 11th 2018
     
    Cost: Simply Ply box, Sealant and some FlexiFoam. I would use Marine Ply next time. I used 'external' Ply and was not impressed with it. Treat the outer cut edge ASAP with some sadolins. No expensive tapes. I got ply cut into lengths in a local workshop to right depth.

    Performance: as good as any other method. Possibly easier to make air tight.

    Ease of install: Box position can be adjusted in every axis. Screw through with packers into inner/outer leaf.

    Only other thing, and this applies to any method, I put a stop bead where the render would meet the window frame, leaving a 5-10mm gap and then filled that gap with expanding foam tape once the render was complete. This worked really well.
    • CommentAuthorgoodevans
    • CommentTimeJan 11th 2018
     
    I think I also like the outboard window box method a opposed to brackets.

    Reasons...

    The wood gives you a solid platform for the windows - allowing traditional packing and fixing solutions.
    Thermally, wood is similar to angle brackets.
    The sub frame jams and head can be located after the windows are placed on the sub-sill if desired - guaranteed, snug fit.
    You have a solid frame to attach flashing and /or air tight barriers.
    The widow frames can be screwed either from the outside or inside to suit.

    Reasons why not ...
    The wood can rot.
    • CommentAuthorMarkyP
    • CommentTimeJan 11th 2018
     
    you can buy a reveal bead for the render to frame detail. it has some rubber fins built in to make a water seal and either a sticky back rubber gasket or strip of expanding gasket for additional seal. I used them and they worked well, but reckon Borpin's method is effectively making your own version of these beads and I expect a roll of gasket and standard stop beads would work out cheaper. the reveal beads werent cheap.
    •  
      CommentAuthordjh
    • CommentTimeJan 11th 2018 edited
     
    Wemico do some very useful frameseal beads https://www.wemico.com/pvc-window-frameseal-beads . Self-adhesive and includes tabs for attaching the masking sheet over the window.

    edit: correct the URL
    • CommentAuthorgravelld
    • CommentTimeJan 11th 2018
     
    What exactly is the function of the yellow strip? Is this the bit snapped off after completion? Is this where a "masking sheet" is attached to protect the window during rendering?
    • CommentAuthorgravelld
    • CommentTimeJan 11th 2018 edited
     
    Posted By: borpin
    Ease of install: Box position can be adjusted in every axis. Screw through with packers into inner/outer leaf.
    To make sure I understand: it can only be adjusted to the extent of using packers, right? AIUI the plywood box slides into the window opening, so the box must always be no larger than the opening (right?).
    • CommentAuthorgravelld
    • CommentTimeJan 11th 2018
     
    For brackets, is there a maximum weight? Or can any weight be carried, as it is a case of a combination of the strength of the brackets and their quantity?
    • CommentAuthorgravelld
    • CommentTimeJan 11th 2018
     
    Posted By: goodevans
    The sub frame jams and head can be located after the windows are placed on the sub-sill if desired
    To make sure I understand: you are here installing the bottom of the box, placing and fastening the window on that, then sliding the jambs and head of the box in and fastening?
    • CommentAuthorgravelld
    • CommentTimeJan 11th 2018
     
    Posted By: MarkyPbrackets - yes, that's the pic I meant (thanks, lazy of me not to link it). In your case I would flip the brackets around 180 degrees but otherwise same approach
    When doing this, I assume if AT tape is to be used the window still has to be touching the continuation of the air barrier? (Maybe it does anyway for stability).

    I just wondered if it was actual best case to be a gap between existing wall and the window therefore next to no heat flow. But if so, should tapes be used where they are bridging fresh air (initially)? Sounds wrong.
    • CommentAuthordelprado
    • CommentTimeJan 11th 2018
     
    Am I being stupid or is this over complicated? What is wrong with just attaching it to your reveals, ordering the window with fat frames, and them insulating external and internal reveals. Thats what I plan to do
   
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