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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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    • CommentAuthorKenny_M
    • CommentTimeMay 22nd 2021
     
    Hi all,
    Recently got old SG sash and case replaced with wooden, DG. The guys did a decent job of fitting but were insisting on leaving air space around the windows for ventilation, suggesting the windows would otherwise rot.

    However, its been bugging me ever since. As per the pic, all the bits with red scribbled over have cold air circulating, presumably coming up from the UF vents via the skirting. Doesn't seem sensible to me to pay for windows with ~1.2 u value then have cold air circulating mm from inside around the rest of the bay.

    I'm inclined to pop the trims off and foam in the gaps between the windows, and squeeze whatever insulation I can behind the panelling. My only concern is that there would then be no cavity between the single outer sandstone skin, and the interior panelling. It is N/NW facing, so there isn't much driving rain, and (as an 1885 add-on) its the only part of the house to have a slate dpc.

    Suppose I am just looking for some reassurance that I am doing the right thing before ploughing ahead, or the opposite if the window fitters were right! :)

    https://www.dropbox.com/s/80ialxhqfeyoqds/IMG_20210522_101338537_HDR.jpg.png?dl=0

    Thanks,
    Kenny.
    • CommentAuthortony
    • CommentTimeMay 22nd 2021
     
    If it was mine I would seal the bottom with foam and pour in small size polystyrene beads to fill all the voids. Icene type foam would work too.

    Definitely seal all draughts and definitely insulate
  1.  
    Be aware that not all squirty foam is airtight. Soudal and Illbruck (probably among others) make airtight foams. I don't think you'd get Icynene in small quantities, as far as I know.
    • CommentAuthorKenny_M
    • CommentTimeMay 23rd 2021
     
    Thanks Tony and Nick.

    The EPS beads are a good idea. I've used these before for filling tight spaces, although its difficult to buy the graphite ones in smaller quantities.

    I looked up Icynene but as Nick says I don't think its easily available for the DIYer. I did a bit of searching for airtight foams and "Soudafoam Window and Door SWS" is has an airtightness rating. It didn't say specifically if it was vapour permeable, but correct me if I am wrong but the spec sheet says μ = 20, which I think is on the vapour permeable side, and the spec also said only 3% closed cell, which I presume would also suggest permeability.

    Not sure if its overkill though worrying too much about how airtight a foam is in my house, which is 200 years old. I guess any foam will be somewhat airtight and probably more airtight than most.

    Wonder if I could do the same thing in the bay with the rest of the outer wall, sealing behind the skirting with foam and then filling behind the lath and plaster with EPS.

    Thanks
    Kenny.
    • CommentAuthorKenny_M
    • CommentTimeMay 29th 2021
     
    From previous threads I see that it is common to add some dilute PVA when filling voids with EPS beads, could anyone give me an idea of the ratio of PVA to water that you use?
    • CommentAuthortony
    • CommentTimeMay 29th 2021
     
    For spraying in with beads 3 water: 1 pva. Beads. An be pre coated with pva and dried, they will then stick together lightly on prolonged contact
    • CommentAuthorKenny_M
    • CommentTimeMay 29th 2021
     
    Excellent. Thanks Tony.

    Now I just need to find out where I can buy the beads!
    • CommentAuthorjms452
    • CommentTimeMay 30th 2021
     
    A variant if you can taking the panelling off.

    Make sure if water gets into the void is gets diverted to outside rather than into your windows (polythene from the inner leaf sloping to outside above the window

    Seal along the bottom of the panelling void and any other gaps to outside with airtight foam and use breathable glass wool something like dritherm 32 in the void.

    Then add vapour barrier behind the panelling taped to the inside of the window frames.

    All easily available and you should have even less water/vapour sitting around the lovely frames.
    • CommentAuthorKenny_M
    • CommentTimeMay 30th 2021
     
    Thanks jms, but I don't think I'm following what you mean by poly above the window, do you mean at roof level?

    Can't think of how else I would be able to run poly from Inner to outer leaf,without taking the window back out.
    • CommentAuthortony
    • CommentTimeMay 31st 2021
     
    I don’t like the idea of fibrous batts, best avoided on this one
    • CommentAuthorjms452
    • CommentTimeMay 31st 2021 edited
     
    Posted By: tonyI don’t like the idea of fibrous batts, best avoided on this one


    I take it you're worried it could get wet and hold water against the frames?

    Drytherm 32 has similar water repellency as poly beads and same lamda, beads easy to pour in if it is all open and wide, fibrous batts easy to fit around stuff. Beads would be great if they fill the void well.


    Posted By: Kenny_MThanks jms, but I don't think I'm following what you mean by poly above the window,


    DIY cavity tray above window - attached a rough sketch. Window fitters may have already done this.

    our (inherited) windows didn't have this and I had to fix it after finding out the hard way
      Screenshot 2021-05-31 at 08.55.10.png
    • CommentAuthorjms452
    • CommentTimeMay 31st 2021 edited
     
    posted in error deleted
    • CommentAuthorKenny_M
    • CommentTimeMay 31st 2021
     
    Thanks for the explanation jms. I am 100% sure that the installers didn't do this, but it does make sense. Unfortunately the only way that I could do this now would be to take the window back out, and not even sure how well it would work as the cavity is at least 150 years in place and won't be uniform.

    We did get some water in at the top of this window during the thaw last winter, so I am concerned about water having nowhere to go once I fill this with insulation. I still haven't got to the bottom of how the water got in, but before the thaw the ice was bulging around the gutters, and I presume it was also bulging to the inside, and when it thawed it was coming down the cavity. If this is right I don't know why it didn't come in at the above window, but maybe it had a clear path until it hit something on the downstairs window then came inwards.
    • CommentAuthorjms452
    • CommentTimeMay 31st 2021
     
    Posted By: Kenny_MI am 100% sure that the installers didn't do this, but it does make sense.


    Quite common unfortunately, seems to be a standard detail for new build but window fitters sign themselves off and do what's quickest and easiest :devil:

    At least on the window's I've DIYed they haven't been attached to anything at the top so it was an easy to fix (but they were uPVC ones rather than your works of art).
    • CommentAuthorKenny_M
    • CommentTimeMay 31st 2021
     
    So where your your cavity tray exits to the outside, is that part left unsealed with a small gap, in order to let the water out?

    I've just been looking at the outside and there is quite a wide bead of silicone at the top, which presumably means that I could possibly cut that out and slip a tray in (or 3 overlapping trays since it is a bay). That could introduce a problem though if I try to fill the panelling in the window above, as any beads would fall down on top of that tray. Maybe a better idea would be to try an access the cavity from the attic and put a lip or tray across the leafs at the top.
    • CommentAuthorjms452
    • CommentTimeMay 31st 2021
     
    Posted By: Kenny_MSo where your your cavity tray exits to the outside, is that part left unsealed with a small gap, in order to let the water out?


    Ours are uPVC windows fitting into victorian cavity (I know, unusual, long story) with an 'arch infill' piece at the top. I just taped the membrane to the inner leaf lintel and sloping down to the front of the window where it was also taped. On replacing the 'arch infill' this covered the membrane and I didn't silicone the bottom the 'arch infill' to leave a small gap.

    If you do a google images search for 'cavity tray above window' you'll get the idea.

    There are probably millions of windows in the UK without this detail so I wouldn't fret too much if you can't do it.

    They're people on here with a much wider experience than me (a keen DIYer) so interested to know what others on GBF think of the importance of this detail too.
      Screenshot 2021-05-31 at 15.35.57.png
    • CommentAuthorKenny_M
    • CommentTimeMay 31st 2021
     
    Thanks for the info jms.

    On further inspection, my bay window appears to only have a single leaf. The rest of the house has two very thick stone leafs, but bay appears to be just the stone pillars with a stone lintel spanning them, then a repeat of that above. My inner 'leaf' is actually the interior wooden panel. Any water coming down on top of the windows in the past would have a clear path down into the sub floor, but once I block that up with insulation it wont!

    Need to break into the attic space above the bay and close any point of entry at the top in case I get a repeat of last winters conditions at some point in the future. At least the EPS balls would allow some draining, but last thing I need is water sitting on top of wooden windows.
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