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Should replacement upvc windows have insulation around them?

FENSA registered company (Anglian) installed new replacement windows. Between the frame and the brickwork there was (at least) a 10mm gap on either side and probably underneath. At the front of the window they have run a silicon bead (sometimes backed up by a polystyrene dowel when the gap is >10mm). But there is still the air gap which I was expecting to be packed with insulation - it was not.

They said that expanding foam would distort the window frame. Hmmmm!

I paid a lot of money for insulated windows to remove drafts. The house is still drafty.

I think breezes are not entering through the window but from around it.

Any suggestions gratefully accepted. Can I ask FENSA to inspect the insulation or the local council?

Additional info:
FENSA said that the air gap is OK. They said that air insulates. However it is important to have a good seal at the front & back of the window to prevent drafts. The former is usually silicon (low modulus) but I do not know about the internal seal.

2 Answers from MyBuilder Window & Door Fitters

Best Answer

Yes, the windows do need room to move e.g. expand and shrink. A white uPVC window can move as much at 5mm per meter thought the coldest winter to the hottest summer.

The 10mm gap is standard for Anglian windows I have always thought it was a little too much but that is the standard gap. I used to fit for Anglian and this is normal for them. It should be covered by a 25mm clocking fillet so you do not see the gap. Also yes, 100% it should have expanding foam around the window. Cut back behind the brickwork then the low modular silicone covered the foam. When I was fitting for Anglian I would have not been paid for the fitting in full I would have had to pay back to cover the re-sealing of the job I did not fit properly.

Windows (UPVC and wood) should have expanding foam around them to comply with the thermal requirements of A rated windows. If not they are not working as they should and so are not fit for purpose.
Windows are designed to be fitted using expanding foam (and fixings as well, not just the foam) and if fitted properly then it will not damage the frame or push it out of square.

You have paid over twice the market rate for the windows so get them back to do it right.


Answered 11th Jan 2014


This to me sounds like poor installation. When measuring for a window replacement the new window should be just slightly smaller than the opening. Then a frame sealant/silicon would be used to seal and eliminate the drafts. Never use expanding foam as this does distort the frame.

If the gaps are over 10 mm I would most certainly get FENSA out or get Anglian out to assess.

Regards John

Expanding foam should never be used on upvc windows or doors although it does have a insulation value. If the seal from front and seal at the back of the window is sound then it shouldn't be a problem for the thermal a rated windows.

Regards john


Answered 21st Jan 2014

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