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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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    • CommentAuthorPaulJ
    • CommentTimeApr 8th 2014
     
    I have a building with lots of sliding sash windows, probably dating from the 1980s. Each pair of sashes has 12 panes of glass, about 280mm x 350mm. They are sealed units 4-6-4. They are held in place with small external glazing beads. Most / many are misted and need replacing, so I plan to upgrade with low e, warm edge spacer and refit.

    What should I do when replacing? I have some glazing silicone, but do I also need butyl putty or other sealant or spacer? Is there a preferred way of doing this? There are LOADS to do so would appreciate any suggestions or pointers.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 8th 2014 edited
     
    Carefully number and cut out all the glazing bars, re-glaze with single 2G units, plane down the removed bar pieces and glue back onto the inner face of the 2G unit (hi-grade double sided tape, or clear silicone) in original position/layout. If you feel the need, make up some corresponding approx-triangular section pieces, to represent the outer, puttied bit of the original bars, glue on similarly. Much better insulating performance (more centre-pane, less lossy edge/spacer), much less trouble, much cheaper.

    Or just leave the glazing bars off - how would that look?
    • CommentAuthorjamesingram
    • CommentTimeApr 9th 2014 edited
     
    Some good threads on here several years back. Have a search around. As above use glazing tape to fix units and beads. Route out main sash to increase rebate depth or cut right out and use smaller bead internally. Make sure to leave drainage space under dg unit
    • CommentAuthorBean
    • CommentTimeApr 9th 2014
     
    Posted By: fostertomCarefully number and cut out all the glazing bars, re-glaze with single 2G units, plane down the removed bar pieces and glue back onto the inner face of the 2G unit (hi-grade double sided tape, or clear silicone) in original position/layout. If you feel the need, make up some corresponding approx-triangular section pieces, to represent the outer, puttied bit of the original bars, glue on similarly. Much better insulating performance (more centre-pane, less lossy edge/spacer), much less trouble, much cheaper.

    Or just leave the glazing bars off - how would that look?


    Wow thats a mamouth task!!!
    Personally think thats a job for a pro joiner rather than a diyer. Don't get me wrong i think Tom is right as regards to performance, but a job to run the bars back and replace the outer with v beads.

    Glazing is always a sticky subject and to be honest there are many opinions and methods which all have there pros and cons.
    My preference is to use a 1mm security tape on the inside all around, unit pushed in,dg unit pack up off the bottom, 2.5mm butyl tape on the backs of all the beads, push up tight against the glass and pinned.
    We machine a small scollop/rebate around the bead so there is a shaper point of contact to the top edge of the bead, this pushes the butyl up and forms a seal between the glass and bead.

    Failing that good old low mod silicon all around inside of rebated up stand, unit in and packed up. Silicon down the sides and top leaving bottom, fine nozzle and bead of silicon between glass and bead.

    Make sure ALL painting is carried out behind beads and rebates.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 9th 2014 edited
     
    How about
    Posted By: fostertomOr just leave the glazing bars off - how would that look?
    • CommentAuthorEd Davies
    • CommentTimeApr 10th 2014
     
    I don't understand the complication here; it's a replacement of 2G with 2G. Is it the assumption that the new units will be thicker? Ie, more than 6 mm gap or thicker than 4 mm glass?
    • CommentAuthorPaulJ
    • CommentTimeApr 10th 2014
     
    Correct Ed. No difference. I am replacing 4-6-4 with 4-6-4 of higher spec. I was just unsure if I should use butyl tape or putty or security tape or silicone or what? Also I was not sure about the "gap at the bottom" school of thought.

    There is no prospect of introducing drainage or ventilation to the panes so my instinct is to silicone all round. There are over 200 to do, so I don't want to be fiddling about.
  1.  
    If you dont leave a gap they may be more likely to blow again
    • CommentAuthorBean
    • CommentTimeApr 10th 2014
     
    No problem with replacing as existing as my post.
    A bit more a problem of removing the glazing bars and reducing if you went down the road Tom advised.
    Although we do all our conservation jobs that way with duplex bar(plant on)
  2.  
    "My preference is to use a 1mm security tape on the inside all around, unit pushed in,dg unit pack up off the bottom, 2.5mm butyl tape on the backs of all the beads, push up tight against the glass and pinned."

    Are these items available at screwfix or similar to collect today? My rebates are 15mm wide, would 10mm width be fine?
    • CommentAuthorArtiglio
    • CommentTime7 days ago
     
    Do you have/want to retain the multiple pane design? If you can do away with it , i’d be tempted to have new sashes (even more so if the existing sashes are in need of work as well)made and go with a single pane. You could add stick on glazing bars to give the multipane look but it can look odd.
    • CommentAuthorvord
    • CommentTime7 days ago
     
    Some caution - When double glazing was first introduced the window manufacturers didn't know how to use it and there were a lot of failures.

    Modern good practice is to have a ventilated air gap around the seal between the 2 panes of double glazing. A gap routed around and ventilation via a couple of holes at the bottom of the channel that also let water out should it get in.

    The seal between the panes is sensitive to many sealants. Best not letting any sealant get near. Mine have rubber seals.
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