I have just had replacement upvc double glazed units fitted. I called the installer back because the transom on one of the windows started to bow downwards. The fitter lifted the transom by putting plastic packers between the the double glazed unit and the bowed section of frame, essentially using the double glazed unit as a structural member. Surely this cannot be good practice! Shouldn't the frame provide the structural ridgity and the double glazed unit just sit within it on packers with no forces on it?

I think you will find there is very little rigidity in UPVC frames, even if they are reinforced. I believe it is customary practice to 'brace' the glass against the frame using packers in the way your fitter has done to ensure everything sits properly. This should have been done right with the packers in the correct places in the first place. Similarly the wall fixings have to be in the correct place with the correct packers used to ensure the frame sits square and plumb in the aperture (with a 5mm min gap all around as well of course). Inherently UPVC frames are wobbly things and need the glass to be corectly installed/braced to provide rigidity.

Hi

If this is a very large window, the a larger frame should have been used, this would allow for good reinforcing and the frame would not bow, this is the same as large frames in conservatories

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Regards Gary Deverson Cosy Living Ltd

email: gary@cosyliving.co.uk