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  • July 4, 2013 at 9:07 am #1350
    philgregg
    Participant

    I recently visited a home where the topic of discussion moved to Better double glazed windows versus another layer of ceiling insulation over existing building code. If you could only finance one which would give the more effective outcome?

    Reading some of the earlier information,  we could improve The window R- Values if we  Thermally break the frame, argon fill and use E glass. The actual R Value improvement seems low but as a percentage is high.  Yet  for the same cost of upgrading from the standard double glazing to the higher spec  we could retrofit another layer of ceiling insulation. As 40% of the heat is lost through the ceiling and only about 25% through the window it would seem obvious to do the ceiling. ……. But what about the moisture issue regarding not having thermally broken windows. Which is worse the heat loss or health issues around moisture?

    I am interested in other people’s perspective

     

    July 4, 2013 at 10:09 pm #1356
    Ian McChesney
    Participant

    Hi – a quick first principles, simple back-of-the-envelope heat loss calculation which may assist (but would certainly defer to others with more expertise, or with access to a good modelling tool).

    I used a ceiling R2.9, increased to R5.4 by adding R2.5. I assumed window started at R0.26 and increased to R0.5. I played around with window area: ceiling area ratio, and assuming roughly the same cost for the two options, it seems to me the window option is better (except in cases where the window ratio is small – and much smaller than is common in houses today).

    July 5, 2013 at 12:41 am #1357
    Norman Smith
    Participant

    If the answer is more insulation or window improvements maybe we are not asking the right question, or not enough questions. Serious double-curtaining and pelmets might the answer but it depends on muliple answers to questions such as “how long do you intend to stay in the house?” , “what sort of underfloor insulation do you have?” , “how exposed is that wall to the wind”, “do you eat/relax or sleep in that room?”   “where is the heater located?” A multi-dimensional matrix of questions is usually required to work towards the solution which seems best to fit the house and the household.

    July 5, 2013 at 8:53 am #1358
    Ian McChesney
    Participant

    I assume the query relates to a house, rather than a single room? In that case I would imagine one is looking for more generic solutions that are robust for various living and family arrangements, rather than tailored to the specifics of individual rooms?

    I would certainly go along with using a broader framework of questions to come up with a ‘best fit’ solution – much along the lines of the ROI discussion. Better curtaining is definitely a possibility.

    Also relevant is the ‘no regrets’ decision – what would I regret most if I didn’t do? Ceiling insulation might be able to be upgraded at any stage in the future, as with curtains. The window decision is a bit more permanent.

    July 22, 2013 at 6:42 pm #1380
    Vicki Cowan
    Keymaster

    Yes a matrix of questions would help.

    But I agree with Ian there’s a critical “missed opportunity/no regrets” piece in the decision making matrix.  If they are planning to upgrade their windows, and just stick in standard double glazing, then probably no further window improvement will happen until those windows are replaced – maybe another 30-50 years? Whereas ceiling insulation could be topped up in a cavity roof, in 12 months time.  So improving the windows should be the priority in my view.  It’s a similar argument with wall insulation, where if people are planning to reline anyway, it should be a top priority to include wall insulation, cos relining also only happens about every 30 years.

    And there are condensation benefits with window upspec’ing as you mention Phil.  Certainly there’s a swag of research that seems to indicate that the dampness (and resultant mould) in our houses is as big a problem as cold when it comes to health outcomes (and makes the problems of cold worse when dampness is added to it). Avoiding having mould growing on the edges of the glass panes, and probably the curtains is probably a significant extra benefit.

     

    July 23, 2013 at 6:39 am #1381
    philgregg
    Participant

    Norman, Ian & lois – Thanks for your input and perspectives. It has certainly given me food for thought.

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