PVC windows make an efficient insulator, but this generally requires big sections with internal steel support, so a well designed aluminium window with low-E may outperform a PVC window with clear glazing.
Having supplied PVC windows in the past, I found that the coefficient of linear thermal expansion of PVC
relative to aluminium and steel was a problem for us. (And if you add in any colour the problem gets even
bigger due to increased heat absorption).
Also,regarding bushfires, they say PVC is good up to BAL 29, butPVCmelts at 180°, and although PVC does not support combustion, a flame is 1200°K ,and also softens at 120 °K,so in a bushfire, the beads holding the glass may melt and the glass may even fall out.
PVC expands at 5 times the rate of the steel, which is in itself a problem for the location of hardware fixing through the PVC to the steel. But more importantly, the increased problem of the level of expansion of the PVC over wide temperature variations found in Australia, which when coupled with the sizes of the windows in rigid walls, can affect the structural integrity of the PVC window or sash, where the window frame components or the sash components have no room to expand.(A 2000mm PVC jamb will expand 6mm over 40
degrees-where does the extra length go? Well it tends to end up binding sashes and frames.)
According to the Australian Bureau of Statistics, the temperature range for Australian capital cities varies as follows: –
Thus there is a maximum temperature range of up to 52°K for all capital cities.
If we look at PVC in relation to that range, the expansion of a a PVC jamb for example, fixed window, or sash, would be: –
(52°K x 2000mm x 0.0000640/°K)= 6.66mm of expansion, whereas the steel would expand:-
(52°K x 2000mm x 0.0000126/°K) = 1.33mm
So that in normal operation over normal temperatures, PVC sashes and jambs “grow” and may bind or bow if confined in a rigid wall.
PVC in Europe
The difference between Europe and Australia is style, in Australia we want big windows, big openings… yes, you can build around the problem of expansion, but why not do what the Europeans do, have smaller windows. Also imagine a dark coloured PVC in sunlight… what temperature will that reach, 70°K, 90°K??
Also, PVC degrades over time to become brittle making repairs and adjustment more difficult.