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Green Building Bible, Fourth Edition
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General: new windows or just new glass?

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    • CommentAuthorPeter Clark
    • CommentTimeNov 18th 2008 edited
     
    We have double glazing about 20 years old, I think its metal clad in plastic, lots of 'misted' units.

    Also we had the cavity walls filled a while back, since then, lots of problems with condensation on the edges of the glass (but not prior to the CWI).

    I am wondering if, instead of shelling out for new windows, we just replaced the double glazing units - Pilkington K, warm edge, argon fill etc. Would the result be anywhere near good double or triple glazing, does anyone have any idea?

    Peter
    •  
      CommentAuthorrogerwhit
    • CommentTimeNov 18th 2008
     
    It sounds like the glass spacer bars are now the coldest part of the glazing and wall surfaces. For solutions, is it possible to estimate the overall thickness of the current glass units? If only narrow units are possible, it might be better to upgrade from argon fill? Warm edge is a definite benefit.
    • CommentAuthortony
    • CommentTimeNov 18th 2008
     
    It also shows that the cavity fill has reduced drafts which previously blew away your condensation.
    • CommentAuthorCWatters
    • CommentTimeNov 20th 2008
     
    Personally I believe ventilation to be more important than anything. We have four of these metal framed windows in two rooms. No thermal barrier in them so you might expect dire condensation on the metal but we've not really noticed any. I attribute this to the whole house heat recovery vent system we installed when building it. The rooms are not overheated. This time of year one room averages 18C during the day (21C in the evening with heating on). Other room is currently unheated and averages about 15-16C in the day but probably colder at night.
      IMG_1495.jpg
    • CommentAuthorPeter Clark
    • CommentTimeNov 20th 2008 edited
     
    Posted By: CWattersPersonally I believe ventilation to be more important than anything


    That is certainly my belief, as a struggling amateur in all this. So we know we will definitely have to address the humidity in our house by ventilation. I suppose I muddied the waters by mentioning the condensation in the first post, probably because that is the impetus for us thinking about the windows.

    I suppose I am really asking in this thread, if we refurbish our windows, including new bang up to date glazing units, how close will we be, thermally, to new double or triple? I don't expect anyone will have a definite answer, but I just thought it might be worth asking. It would certainly be less expensive for the bank account, what about the environmental impact?

    Peter
    • CommentAuthorPeter Clark
    • CommentTimeNov 20th 2008 edited
     
    Posted By: CWattersI attribute this to the whole house heat recovery vent system we installed when building it


    Thanks CWatters,

    We have looked into this also, the main issue is the requirement for airtightness, which is said to be crucial. So it is difficult to justify spending the money on the MVHR, and the airtightness modification, unless we can get it down to 3 air changes per hour at 50 Pascal. But when I approach contractors, no one can guarantee that they can achieve this for a sixties semi with suspended wooden floors.

    Any advice on this would be welcome.

    Peter
    • CommentAuthorJackyR
    • CommentTimeNov 20th 2008
     
    I'm a complete ignoramus in this, but I when spoke to an MHRV company techie about this and other issues (disused chimneys as ventilation ducts), he didn't seem bothered about airtightness. We eventually agreed "the more airtight the property, the better value you get from the MHRV".
    • CommentAuthorPeter Clark
    • CommentTimeNov 20th 2008 edited
     
    Posted By: JackyRwhen spoke to an MHRV company techie about this and other issues (disused chimneys as ventilation ducts), he didn't seem bothered about airtightness


    I have had the same experience with companies who install MHRV. But when I spoke to a company who supply the kit, who I have reason to trust, they said it was not worth the bother and expense, unless airtightness was 3 air changes or less per hour at 50 pascals.

    I don't KNOW who to believe, but the latter advice seems more believeable, if less convenient.

    Peter
    • CommentAuthorJackyR
    • CommentTimeNov 20th 2008
     
    Oh well done - that's exactly the sort of figure I wanted from the MHRV co and they c/wouldn't give!

    But the Q remains, what sort of ventilation is efficient (in cash & energy) to solve condensation probs, given one needs SOME.
    • CommentAuthorPeter Clark
    • CommentTimeNov 20th 2008 edited
     
    Posted By: JackyRBut the Q remains, what sort of ventilation is efficient (in cash & energy) to solve condensation probs, given one needs SOME.


    I started another thread 'What type of ventilation to retrofit', I am hoping to achieve some clarity.

    Peter
    • CommentAuthorCWatters
    • CommentTimeNov 20th 2008
     
    Posted By: Peter Clark
    Posted By: CWattersI attribute this to the whole house heat recovery vent system we installed when building it


    Thanks CWatters,

    We have looked into this also, the main issue is the requirement for airtightness, which is said to be crucial.


    It might have an effect on the energy saving aspect but seems not to be a problem for ventilation. We have two chimneys with stoves but they aren't room sealed types. The company that made our other wooden windows also fitted trickle vents in them without us asking for them. We keep these closed but they aren't air tight and we didn't make any special effort to design an air tight house although it was wet plastered which helps.

    The vent system has two fan speed controllers so we can choose if air goes in or out of any leaks - anyone know which is worse? We currently have both on the lowest speed setting as it's winter. We turn it up in summer to get a higher air change rate.
    • CommentAuthorPeter Clark
    • CommentTimeFeb 5th 2009 edited
     
    I have moved this from the Triple Glazing thread in New Building, where it seemed a bit inappropriate.

    I am still wondering how reasonable to renovate my aluminium windows, rather than buy new’uns. The prices for triple make my eyes water.

    Posted By: Peter Clark
    Posted By: ralphdI used some foam in a can to fill the cavities & fixed the problem.

    Hi Ralph,

    You mean you filled the cavities in the PVC frames?

    It has crossed my mind to try this with our aluminium frames, but I dismissed it as a mad idea. Can you say how you did this? Were the frames in place in the building?

    >Posted By: Peter Clark
    Posted By: howdytomif your alloy frames are a one piece extrusion, ie no thermal break,

    then the alloy will still conduct the heat around any infill insulation.

    you could drill 6mm holes then after foaming fit grommets

    Posted By: Peter ClarkThanks Tom,
    The frames have a thermal break in, i believe, so maybe filling with something insulating would not be possible, or useful?
    I am having trouble visualising it, I have never seen a window frame other than installed into a wall, so i don't understand how they are constructed.

    peter
    • CommentAuthorralphd
    • CommentTimeFeb 5th 2009
     
    Most my frames have holes in the sides to screw into the rough opening. I stuck the straw from the spray foam can into the holes and pulled the trigger...
    With aluminum frames (even with thermal break) this probably wouldn't help much.

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