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Housing - Renovation: replacing failed double glazing units, advice sought

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    Cedar windows, about 22 years old, still very sound, but about 50% of the glazed units have failed over the years.
    I Need about 30 glazed units ranging from(nominally) 18" by 24" to 24" by 30".
    Old units were the thinner type 4-13-4, but the rebates are a carefully measured 41mm or 1 & 5/8".
    So I could/should get away with the standard 4-16-4 units?
    Questions
    (i) I am seriously considering doing the work myself, I have already removed one unit without fuss, so it seem a feasible proposition for me to take on, over the summer being retired.
    (ii) Should I consider replacing ALL the units? and I have no idea re costs, yet.
    (iii) What spec should I be looking for in the units?
    Regards, in anticipation,
    Marcus
    Re item (ii) I probably need to replace most all of the units, since most windows are multiple glazed units, or beside other windows and it would look odd otherwise. Except for the odd unfailed single window here and there in bathrooms etc, which I would gladly leave.
  2.  
    <blockquote><cite>Posted By: orangemannot</cite>Old units were the thinner type 4-13-4, but the rebates are a carefully measured 41mm or 1 & 5/8".
    So I could/should get away with the standard 4-16-4 units?</blockquote>

    I assume the existing units are held in with wooden beading. Replacing with 4-16-4 units should not be a problem, a beading with a depth of 15mm or less should fit. You could probably squeeze a 3G unit in e.g. 4-8-3-8-4 = 27mm or even 6mm spacers giving a unit of 23mm which is only 2mm mote than original, but the cost will be higher and the increased thermal efficiency may not be worth the extra. Although noise attenuation is a different matter.

    Somewhere there is an on line calculator for u values for various glazing units but I can't find it now, but if someone else can point to it it would help with the cost/benefit calculations.

    I would go for argon filled low e units with warm edge as these are (should be) easily obtainable and the warm edge is defiantly worth the extra IMO. I would also make sure that the new units are held off the frames by small spacers placed at the bottom of the units.

    Very DIYable, probably the hardest part would be getting the old beading out without (too much) damage if you want to reuse the beading.

    Whilst you are in 'window mode' are any rubber seals in good nick?
  3.  
    Soft-coat low-emissivity glass, in case anyone is still selling hard-coat.

    Yes, go for 4/16/4, argon, low E and warm-edge spacers as described.

    Some use glazing tape. Others use silicone, low modulus, I think, but anyone care to clarify? Of course it's a b---er to remove if it splurges over.
  4.  
    Thanks Nick, and Peter, just what I was after, spec wise.
    I would like to re-use the existing, mostly sound hardwood/Cedar beading, if only because very recently I spent an indecent amount of time*** sanding them and the rest of the frames down to the sound bare timber before resealing all with Osmo UV Oil.
    The upstairs unit I removed, off a ladder, came out simpler than I expected by dint of driving a large Sabatier type kitchen knife full-length into the most likely looking seam between the frame and the glazing slip and then carefully hammering the blade sideways, and then cutting the just exposed panel pin(s) through the gap created(with a bare hacksaw blade) to remove the first glazing slip, the other 3 were then esay-peasy.
    The DG unit was held in-situ with moderate amounts of relatively easily removed silicone, fingers crossed the rest will be the same.
    I would probably go for the glazing tape rather than the silcone.
    ***Like one full 1/2 Hr pr slip, times 4 per unit, times 4 units per window!
    P.S.
    Arse about face as most always I am, in that I knew I really really should have replaced the failed units prior to lovingly sanding and resealing the windows.
    Doh!
    • CommentAuthorjamesingram
    • CommentTimeMay 18th 2019 edited
     
    do they have a drainage space underneath them in the sash ?
    What's the thoughts on this? I was under the impression units were more likely to blow due to condensation forming at bottom of unit.
    • CommentAuthorCWatters
    • CommentTimeMay 18th 2019
     
    +1

    Installation issues can be the main cause of failure. Try and use flat spacers so both panes of glass are supported rather than wedges which only support one of the panes.
  7.  
    Posted By: Peter_in_HungaryI would also make sure that the new units are held off the frames by small spacers placed at the bottom of the units.
    • CommentAuthorCWatters
    • CommentTimeMay 19th 2019
     
    Sorry, didn't mean to repeat your advice, my point was they should be flat spacers not the wedges some installers use.
    • CommentAuthortony
    • CommentTimeMay 20th 2019
     
    For me and crucially I would drill three or four holes downwards through the bottom rails of the sashes, 8mm and if the fixed panes are direct glazed I would drill so the holes come out in front of the face of the wall.

    I hate glazing rebates that are not laid to falls outwards and would adjust these with a rebate plane or router.

    Additionally I would also sit the bottom bead on 3 or 4mm packers so that water could not possibly collect under the unit.

    This as well as the packers mentioned above

    Proper 3x belt and braces failsafe installation of dg units
  10.  
    Posted By: CWattersSorry, didn't mean to repeat your advice, my point was they should be flat spacers not the wedges some installers use.

    Not a complaint - just reinforcing the importance of the spacers, as did Tony with additional safeguards.
  11.  
    All good stuff, and indeed the bottom rebate is "dead flat", nor does it have drain holes drilled, so that was useful to know.
    However if I chamfer the bottom rebate, how do I evenly support the glazing unit on flat spacers, or do I only chamfer the outer bit for the slip?
    Any merit in routering a drainage groove, with the 8mm weep holes drilled outwards from the bottom of this groove, for the spacers to bridge across
    So essentially one is aiming for a 3 to 4mm well drained air gap below the unit, and 2 to 3mm? clearance around the sides and top.
    Got a price just now, £400.00 (+VAT) for the 27 units, so about £15.00 per unit, to the specification as provided above and it only took 15 mins for them to respond with the price, very very professional.
    Regards, and many thanks,
    Marcus
    • CommentAuthorTimSmall
    • CommentTimeMay 20th 2019
     
    There's often a choice of spacer colour (e.g. grey, white, black), so consider what will go well with your windows. Also double check that they're going to supply "warm edge" spacers.

    For glazing their own timber windows, Green Building Store used to supply (maybe still do), interlocking sets of wedge spacers (they had toothed surfaces, so that pairs installed opposing each other would lock, and the thickness could be adjusted in place, but were sufficiently toothed that they would not slip in use).

    I really like them for timber sashes (lookup spacer positions online). The only equivalent I could find last time I needed some were from toolstation ("Roughneck Plastic Floor Packer Set").
  13.  
    (i) Puzzled as to how the spacer colour could be seen after units and slips were fitted?
    (ii) I specified, per the specification kindly supplied by Nick Parsons above, "warm edge " spacers when asking for the price.
    The Green Building Store product Sounds like serrated "folding wedges".
    Cheers
    Marcus
  14.  
    Posted By: TimSmallThere's often a choice of spacer colour (e.g. grey, white, black), so consider what will go well with your windows. Also double check that they're going to supply "warm edge" spacers.

    Posted By: orangemannot(i) Puzzled as to how the spacer colour could be seen after units and slips were fitted?

    I think the spacers to which Tim refers are the spacing bars between the panes of glass which are visible when looking a bit sideways at the glazing units. In the old days before warm edge spacers they were all aluminium coloured.
  15.  
    Ah!,
    Yes ALL too aware of that issue, since the existing windows were supposed to be coming with the 4-16-4 units and the bronze finish,(verbally specified only as part of a "the same as the windows in the house in the town specification") but I got the bog-standard 4-12-4 bare aluminium spacer ones instead, i.e. EXACTLY the same as the windows in the house in the town!
    thanks Peter
    EDIT
    Perhaps "packers" would be a better descriptor for the spacers used to centre the glazing unit in the frame.
    The same term for different elements of one construction is fraught with the possibility for confusion,
    cheers again
    Marcus

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