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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    Can anyone tell me what is the most efficient reasonably traditional-looking sliding sash window on the market today? I don't mind much about the actual material, so long as it looks good.

    I think airtightness is fundamentally more important than U value, because you can add extra insulation elsewhere (to some extent), but you can't add extra airtightness. (I would want to use MHRV.) This suggests to me that a "manufactured" solution will be better than something handcrafted, but I guess that's not necessarily true. I suppose the best U value for the glass will be soft coat with Krypton fill and warm edge? Does anyone use that?

    Brands I know about:

    USA: Marvin, Andersen
    UK: Masterframe, various timber manufacturers (which is the best?).
    Europe: Vrogum
    • CommentTimeNov 13th 2007
    Custom-made authentic ones can be as efficient as any:
    Nowadays I'd increase the sash depth (measured from inside to outside) from 56 to 62mm, to allow optimal 16mm gap DG units.
    Some people in the trade think sash windows "are fundamentally flawed".

    See http://www.thermotechwindows.com/Column3.htm

    BTW, I have no affiliation with Thermotech but suffered from old leaky sash windows until we changed them for casement (which actually matched the rest of the house in case anyone is wondering if I vandalized an old property).

    Paul in Montreal.
    • CommentTimeNov 13th 2007
    True, sliding sashes are wierd, but they're here to stay. They're specially good when they're huge, like 3m high x 1.4m wide, as in posh Georgian 1st Fl - that's why they got popular - no way could you do that, sidehung, in 1736, or even now. These huge sashes used styles and top rail only 44x44mm; in Bath Georgian the meeting rails were only 16mm high x 56mm deep! - without horns, so barely any through-tenoning - many still going strong 270yrs later. Stupendous structural economy - structural glass, in fact. After the Great Fire of London, Building Acts outlawed all combustible material on facade, so window fixed frames were fully hidden behind a nib of masonry, leaving only flimsy sliding sashes exposed on face. Bath Georgian box frames don't have a cill either - the sash bottom rail 56-69 high x 44 deep comes right down onto the stone subcill.
    • CommentAuthorbiffvernon
    • CommentTimeNov 14th 2007
    And for the smaller window, say around one metre square, the Yorkshire Sash, in which half is fixed and the other half slides horiziontally, is an excellent solution. It pre-dates the vertically sliding top-hung sash window yet is particularly fit for the 21st century. There are no moving parts such as cords and pulleys to go wrong, simple and substantial construction, and easier to make draught-proof.
    • CommentTimeNov 14th 2007
    Posted By: biffvernoneasier to make draught-proof.
    • CommentAuthorbiffvernon
    • CommentTimeNov 14th 2007
    Seven potentially draughty edges as opposed to three.
    • CommentAuthorsuecar
    • CommentTimeNov 26th 2007
    Apparently Passive House Solutions are working with a uk window manufacturer to develop passive house standard sliding sash windows at present.
    suecar, have you a link for that?

    How are they hoping to achieve it? Seems extremely difficult to me. I can't imagine a triple glazed sliding sash window, and that is the only way you would get the U(glass) values you need. It would be very thick and heavy, unless there's some sort of secondary glazing arrangement. Even then, I can't imagine the mechanics of it.

    I guess you could use suspended films in a 3mm soft coat, 9mm krypton, low-e film, 9mm krypton, 3mm float configuration for a 24mm unit (0.675 according to WINDOW 5), but I don't think anyone manufactures those in the UK.

    And that's just the glass. What about the frame?
    • CommentAuthorarthur
    • CommentTimeAug 15th 2009
    <blockquote><cite>Posted By: suecar</cite>Apparently Passive House Solutions are working with a uk window manufacturer to develop passive house standard sliding sash windows at present.</blockquote>

    Anyone heard any more on this development since its nearly two years on from that post now?
    theres a place in york called swedish timber products or something. think their triple glazed windows go down to u-value of something like 0.8w/m2k. which is quite impressive (thats better than some old uninsulated walls haha
    • CommentTimeAug 21st 2009
    Vrogum from Winchester Joinery do the most convincing hi-tech sash window I've seen, only 2G but still ... Vrogum tho expensive are something different amongst Scandinavian window manufs, superb looking and unique as they're glaze-in, not glaze-out. That fortuitously gives an external appearance that is near-indistinguishable from trad English cottage windows, also Georgian/Victorian etc, all in 3G (incl above mentioned 2G sash windows). And internally OK too. I was talking to Russell, and I'm sure there's no reason why they shouldn't source something similar from their pan-Europe suppliers' web, at a price that's no reason to be higher than their present lo-cost offering.

    Swedish Timber Products do SP windows, next cheapest after Russell. Basically near-identical kit.
    fostertom, do you have any higher res versions of your construction drawings above? can't quite make some of it out.
    thanks if you can


    from vrogum

    "Upon opening the window the sashes are sheared, thus avoiding wear on the weather strip . On closing the window the sashes are being pressed against the weather strip, making the window shut extremely tight."

    then had a look at http://www.vrogum.co.uk/?page=rosenholmprofiles

    eg f107,

    and now feel i am a long way off being able to compete.

    not sure what you mean by 3g being indistinguishable, seems they're all 2g apart from glaslux which is 3g, but it has coloured perimeter glass to look like frame/hide inner frame. ie that's glaze out
    • CommentTimeSep 4th 2009
    Posted By: spoonandforknot sure what you mean by 3g being indistinguishable, seems they're all 2g apart from glaslux which is 3g, but it has coloured perimeter glass to look like frame/hide inner frame. ie that's glaze out
    Not sure what that means ... I meant that the outer face of the glaze-in timber frame, together with the outer glass face, are indistinguishable from English cottage - nothing to do with 2G/3G, not about hiding any spacers you can see thro the glass etc.
    I too am looking for energy efficient sash windows. We're very eager to get the windows to look as close as possible to original Victorian sliding sash windows.

    We've had a local tradesperson round who can make beautiful-looking wooden sash windows with a u-value of around 1.9 - 2.0.

    So I'm hunting for a good value, authentic-looking, high performing wooden sash.

    I looked up Swedish Timber Products but I couldnt see any sliding sash windows on their website

    I've contacted EnviroNomix.co.uk (Vrogum) to ask for a quote. Over the phone they suggested they could achieve a whole-window U-value of 1.4 for sliding sash. My wife, in her research, also looked into EnviroNomix and came to the conclusion that the frames are too plain (none of the little flourishes you see on original Victorian sashes).

    (we're insulating our walls to a U-value of 0.28).

    I'm wondering if could use our local window makers to make the frames but provide them with a high performance double glazing unit?

    So could anyone recommend a supplier of just the double glazing units? And/or a supplier of high performance wood sash windows?!?

    Posted By: dan_aka_jackI'm wondering if could use our local window makers to make the frames but provide them with a high performance double glazing unit?Jack

    Hi Jack

    We made our own up and down sash windows last Autumn, we used 4*12*4*12*4 Krypton filled glass with warm edge spacers. I think the overall U-value of the windows is close to 0.8 inc frames. The secret is to use warm edge spacers that are the same colour as the frames. The difference in the heating bills and comfort of our 1880's red brick house last winter was unbelievable. The convection currents have been totally eliminated.
    Wow, 0.8 - that's very impressive. Would you mind guiding me to the place where you bought your lovely glass? Did you make your frames completely from scratch or did you start with an original sash frame?

    (I'm very new to windows so these questions might be remarkably stupid)
    I bought the Triple Glazed glass packets from an Irish glazing company Carey's Glass, they use St Gobain glass.
    Viking House, can you upload some pictures somewhere?
    Interesting progress made yesterday: I phoned our local joinery company to say that I love the look of their windows but I'm not so happy about their u-value (2.0). I suggested that if they give me the precise size of the double glazing units they require then I'll source high performance DGUs to fit their specs.

    At this point in the conversation, the guy stopped me and said: "Jack, may I ask why you want a u-value of 1.6 or better?" and I said "because we want to save on gas". It turns out that he received a letter from the local authority on Friday warning that the new Part L may require all windows to have a u-value of 1.6 or better. He wondered if I had seen that (I was aware that a new Part L was coming into practice but I didn't know the precise u-value requirements)

    Anyway. The local joinery company was only too happy to take the few notes I'd made about UK suppliers of high performance DGUs (including Carey's Glass, many thanks @VikingHouse!) and now they're looking into getting new, higher performance windows. So, hopefully, everyone's happy: I get high performance windows and the local window company gets a bit of free research about high performance DGUs. Fingers crossed it works out...
    • CommentAuthorJoiner
    • CommentTimeApr 28th 2010
    Apropos that last post…

    Do your local joinery shop a favour and make sure he’s read this…


    And for a very general overview…

    Posted By: Viking HouseWe made our own up and down sash windows last Autumn, we used 4*12*4*12*4 Krypton filled glass with warm edge spacers.

    Do you have any aesthetic concerns about using such wide glazing units in sash frames?

    The reason I ask is because our local wooden window joiner is trying to persuade us that we should use the thinnest available DGUs because wider glazing units "look ugly in sash windows". His preferred DGU is a 3-4-4 (11mm total) DGU with a U-value of 1.6. Not too shabby, but I'd be happier closer to 1.2 (or lower).

    So - is he correct that wide glazing units "look ugly"?

    (It's worth noting that our local joiner spends a lot of time making windows for listed buildings and he has a strong interest in conservation, so he's obviously got a keen eye for the "authentic". But, to be honest, I'd rather have high performance in a window which looks, from a few meters away, authentic rather than a window that looks authentic when inspected from 10cm away).
    If your windows are going to be painted white and you use white spacers between the glass then your eye only sees two thin 4mm lines where the glass goes through the spacers.
    They are not glaringly obvious like aluminium spacers.
    The frames can be as thin as before if you use the glass packet as a structural element and silicone it to the frame using some of the better silicones. The sashes are lifted on both sides by the rope so there is no diagonal weight load. The 3x glass, the frame and the silicone compliment each other making it a very strong unit.
    If I was back again making my windows I would have made the sashes much thinner.
    The 3x windows now being produced in Germany have much thinner frames than the ones from 15 years ago because they started to notice the structural stability of 3x glass.

    They don't look Ugly but nothing stays the same
    Excellent info, many thanks. I'll discuss with the local joinery company.

    (by the way, there's an interesting article on Building.co.uk about a Japanese double glazing unit with an overall thickness of 6mm and a U-value of 1.4. It achieves this impressive U-value by maintaining a vacuum between the two panes of glass. http://www.building.co.uk/story.asp?storycode=3139081 )
    Interesting reading these tips. I was also wondering who does the best mock-sash windows. Sliding sashes are always going to struggle to keep up with the performance of tilting or casement windows it seems but is there any reason why it shouldn't be possible to have a convincing (from a distance, until you open it) mock sash window that doesn't actually slide. The ones I've seen don't seem to look too good.
    • CommentAuthorBeau
    • CommentTimeOct 7th 2014 edited
    I have built traditional sliding type sash windows with excellent seals and DG panels. Just straight forward joinery with a design to incorporae seals from this firm https://www.mightonproducts.com/
    • CommentAuthorringi
    • CommentTimeOct 7th 2014

    Have you got any air leakage test results for your windows?

    How do you get them past building control given they will not have an approved energy rating?
    • CommentAuthorBeau
    • CommentTimeOct 7th 2014 edited
    <blockquote><cite>Posted By: ringi</cite>Beau,

    Have you got any air leakage test results for your windows?

    How do you get them past building control given they will not have an approved energy rating?</blockquote>

    No tests done and only replacement windows for a house with single glazed leaky sash windows. Building control what's that :wink:

    I don't suppose they would hold up against some of the offerings available these days but massively better than a traditional sliding sash window that they replaced.

    If you require BCO approval this might help http://www.part-l.co.uk/ecosash
    • CommentAuthorslidersx200
    • CommentTimeOct 7th 2014 edited
    If you can accept PVC as a suitable material, Eurosash made by Dungannon Windows in NI have halved the effective air leakage compared to other manufacturers using the same (Spectus) profile. They will also fit triple glazed 28mm krypton filled units with a centre pane value of 0.7W/m2K and can achieve a whole window U value of 1.1W/m2K, subject to size and choice of glazing bars.

    I would say these are among the "higher end" in PVC terms, having run through horns and mechanical butt joints rather than welded mitres. You have to ask for a deeper bottom rail if you would prefer it.

    Another company I am seriously considering for our build is Baird's Windows in Scotland. They offer wooden windows, made from engineered sections (red grandis by default) and up to 44mm triple glazed units with argon fill for a centre pane value of 0.6W/m2K and an overall U value down to 1.0W/m2K, again subject to favourable sizing and a "one over one" design. *Be warned though that these are a rather chunky ~200mm deep window overall, although slimmer double and single glazed options are available.

    Their software gives the U value for each window and although no formal permeability testing has been done, I was told that they could take a sample to a test rig if it proved proved pivotal in my decision. They do include a double seal at the meeting rail and use predominantly Q-lon seals, so hopefully they would fare well.
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