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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorYanntoe
    • CommentTimeJul 27th 2020
    In my efforts to increase the dryness and warmth of my Victorian pile, I've had to remove the Palisades from around 4 large Box Sash windows.
    I now have to modify the exterior frame to close up the gap between the window frame and the stone work before adding a weatherband round the perimeter of the box sash.

    The windows are a very poor fit and the box frame is actually not a box as there is no closure of the frame against the wall - so its a three sided box. Perhaps this is normal, but it does mean that the box is a cold bridge with, effectively, only a 20mm piece of timber between the outside and the inside of the house. It also means that along with the holes for the window cords, noise comes through the window with great ease! So, the window is cold and noisy, and the inside of the box has all the insulative and waterproof properties of an old garden shed!

    I would like to address this in at least one of the windows but am not sure what to do.
    Options to date are;
    1) remove the weights and cords and blank off the pulleys, fill the box with foam and seal the window closed. Close outside "gap" with akoya cover slip and add a mortar weatherstrip.
    2) ditto, but try to insert Rockwool into the box rather than foam
    3) ditto fill the box with some kind of lose fill eg Leca (or something else.)

    Clearly foam is the easiest and probably most effective in terms of air movement/insulation/ and noise reduction, but I'm rather nervous about using it. Not sure why, so can someone tell me whether it's a bad idea, or indeed share some success with doing something similar?

    I'm limited to how much I can do, i.e. the external access is all there is and I can't modify the wooden frame, or replace the windows (again) .

    So, any advice would be greatly appreciated.

    Many thanks
    • CommentAuthortony
    • CommentTimeJul 27th 2020
    Presume you are going to use spiral balances instead of weights?

    I would foam the window in place, is it loose?

    I would fill the Box with eps beads.

    Lime mortar before any wood strips.


    can use it to fill the very top if beads too difficult

    Aim for air sealed all round frame inside and out over and under
    • CommentAuthorYanntoe
    • CommentTimeJul 27th 2020
    Thanks Tony,
    for vanity, I guess, the Victorians put 2 sash windows, each 1.7m high and 1.3m wide in rooms of 4m square. The rooms are light, but the windows are so big and face the weather (W) and North that they are not as warm as one might like in the winter!
    I'm actually going to completely seal shut the worst of the windows - So I'll leave one functioning properly and try to improve the other of the pair (per room). I have experience of the "exuberant" use of foam as you describe, but is there any other reason not to use it to carefully fill the box?

    I tried to use eps beads to insulate the void between the head of the window and the stone lintel outside - the resultant Snowstorm in June has led to me being banned from using EPS beads in future (I did suggest it, but was soundly rebuked).
    Historically I've made celotex "gaskets" scribed to the gap between the window and the wall and lightly foamed these in place, but if I'm going to render the window non-functional I thought I should try to improve on the seal and insulation whilst I was at it.

    I'll repair/repoint the stonework round the window first and then scribe some durable wood to form a band around the window and to keep whatever it is I fill it with secure and form a base for the weather band.
    • CommentAuthorrevor
    • CommentTimeJul 27th 2020
    Have you got room inside to add to the frame to make it thicker and insulate that. Then I would add secondary glazing to this frame the gap between the secondary glazing and the primary glazing will give you sound proofing and heat retention. If the window is situated in the middle of the wall then there should be room between the frame and the inner side of the wall so maybe make the secondary glazing fit flush to that.

    I have refurbed several sash windows and made identical replacements and fitted secondary sash glazing but at the time insulation was not as high on the agenda so did not do what I have suggested here, but I could have done.. Do not make the window unusable they are the best design of window I have come across. You will regret it so try and make the best of what you have there. The ability to ventilate the house using either the top or bottom sashes the top great for draught free ventilation is a great benefit.

    The open sided box section housing the weights is a typical feature and over the years rubble and mortar drops into it which is very annoying causing the weights not to bottom properly. When I made them I completed the "box"

    The other consideration do any of the windows give you a means of escape from a fire?
    • CommentAuthorYanntoe
    • CommentTimeJul 27th 2020
    Thanks Revor,
    Yes - I too like sash windows, but these are poorly made as the boxes are not absolutely square which meads they have to fit loosely to be able to open/close easily. However, its the box which is the focus at the moment as I have to fix the outside "seal" of them when I replace the palisades with new weather bands. AS there are two enormous windows per room, the opportunity to ventilate is OK, even when only one works, so no great loss there. On the inside the windows have shutters or are panelled which complicates adjusting the inside aspect.
    Good info about the box construction - thanks.
    • CommentAuthorowlman
    • CommentTimeJul 28th 2020
    Rockwell RWA 45 acoustic batts are semi rigid and cut easily. They may be an option for the boxes as you can slightly oversize them to create a snug fit. You could also consider expanding neoprene tape for awkward sealing jobs. Specialist suppliers have many different expansion types and sizes
    • CommentAuthorYanntoe
    • CommentTimeJul 28th 2020
    Thanks Rockwell,
    I think the wall batts might be a bit friable - but a good thought. We've used the expanding neoprene round various window joints so that too is a good suggestion.
    The void in the "box" adjoins the old lime pointed wall, so I was wondering how mineral wool products would cope with the moisture in this situation. It would be tricky but not impossible to "feed" mineral wool into the void to get a pretty full fill (hopefully), but would it cope with the high moisture levels without loosing its insulative properties or "sagging"?

    Any thoughts on this?
    If you already have problems with water ingress I visualise a sponge!

    I cannot remember whether it was glass fibre or rockwool, but I remember wringing water out of mineral wool in a poorly-ventilated roof once.
    • CommentAuthorYanntoe
    • CommentTimeJul 28th 2020
    Thanks Nick - OK, I'm moving towards EPS bead, full fill, with "celotex" gasket at the outside edge and top plugged with foam. All covered with Accoya weatherstrip and then mortar weather band to the outside.

    Measured temperature of walls (18C) Glass (17C) and sash box this morning (16C) so the "weak link" does seem to be the sash. Outside temperature overnight 11C and today up to 15C - no heating in room for several weeks. I guess in the winter it would really show up as the internal temp is only a few degrees above the external temp at the moment rather than the (hopefully 15C difference in mid winter!
    • CommentAuthorYanntoe
    • CommentTimeAug 18th 2020
    Removed the external cement mortar decorative surround from one window. Clearly there is a water mark on the outside of the internal wooden lintel, but there is no crack or hole in the lime pointing anywhere on the wall (I've checked it inch by inch from scaffold!).
    I've made a Celotex "gasket" which fills the gap between the outer leaf of the window and the wall and foamed this in. As suggested by Tony, I've then added EPS beads to the box and filled the entry hole with foam. Still have to repoint and repair the corbelling round the window, add a wooden cover slip and then add a small window band.

    Within a day or two, the wet patch on the inside of the reveal reduced in size by 50% and now, after three weeks is fading away - despite biblical amounts of rain last week.

    The temperature of the inner leaf of the window is now the same as the internal plaster work and 1 degree warmer than the double glazed unit in the wall (OK - not a big deal in the summer, but it is a change from being colder than the wall and the glazing 3 weeks ago).

    It does mean that the window no longer opens but there are two in the room so a sacrifice worth making I think.

    Looking at the old cement mortar decorative surround, it seemed to be acting like a dam - there was a 300mm slightly darker look to the pointing at the windward/rainy side of the window. So water moving down through the pointing accumulated at the concrete band and then moved in via the reveal. It was damp behind the Cement/Mortar band header and the cement itself was also damp (OL on damp meter) all the way round.

    I'll repeat on all the other windows as soon as weather allows and see what I find. However, I can't seal these so they won't get so well insulated.

    I am going to use Stormdry on the weather face - so we'll see whether this helps make the house dryer (and warmer) or not.

    So thanks for the help with this - as much as I hate EPS beads they seem to have helped in this application.
    • CommentAuthortony
    • CommentTimeAug 18th 2020
    • CommentAuthoraclarky
    • CommentTimeAug 30th 2020 edited
    How did you get on? We are just about to do ? 15 windows - plan is expanding foam bottom and top and EPS fill although our window boxes have significant gaps where they meet the stone and so wondering if we fill the wooden surround too..
    As above, another thought was to gradually fill the boxes with expanding foam but I think as well as the deflection issues I would be worried about water / condensation issues.
    I wondered about vermiculite - any body has any ideas re this - I think it could still be blown in with a gun and better fire rating, not sure re environmental + / -'s..

    If anyone is interested we are going with Pilkington Spacia glass - link below. For sash refurb it seems a pretty useful material. Basically 2shets of glass held apart by <1mm glass beads and sealed and vacuumed, good U value, only 6mm thick so more sympathetic aesthetically and doesn't fail like slender double glazing.

    It is made in Japan where its been used for years - cost wise - for each sash to be glazed and routed for brush seals is costing us about £900, which is a lot but pretty competitive I think, in Glasgow. Will let you know if it is any good.


    can we share phone numbers on this forum? Would be good to know how you got on.
    Also wondering about the void at above the window too or is it straight onto the lintel?
    • CommentAuthortony
    • CommentTimeAug 31st 2020
    Vermiculite can hold water so I would rule it out as not fail safe
    ''can we share phone numbers on this forum? Would be good to know how you got on.''

    Would suggest a whisper direct to Yanntoe.

    ''Vermiculite can hold water so I would rule it out as not fail safe''

    Agree with Tony. I used it to fill a redundant flue but made very sure before doing so that the risk of moisture was minimal. I think with windows the risk of absorption due to failing seals between window and masonry might be a bit high for comfort.
    • CommentAuthoraclarky
    • CommentTimeAug 31st 2020
    perfect thanks Tony and Nick :)
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