Filling new sash windows in bay window

1 Aug 2011
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United Kingdom
We recently (a year or so ago) had new wooden sash windows fitted in bay windows. Where the sashes meet between the centre sash and the 2 outer ones the fitter put flat beading on each side to cover the gap. Unfortunately there is a significant draught coming through between the 2 pieces of beading, and when I pushed a piece of paper through the gap it was obvious that there are large gaps behind between the sashes. Can you recommend a suitable filler to fill the gaps? I assume some kind of expanding foam filler would be best. Does it need to be flexible to allow for movement in the wooden frames? I should be very grateful for definite recommendations, so we can get this done before the winter sets in!

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Expanding foam will seal the sash shut, permanently.
Brush strips can be used but sash windows are draughty by nature.
I obviously didn't make myself clear. The gap is between the windows, not between the sashes. There are 3 separate but adjoining windows, each with 2 sliding sashes. It is the angles between them that are causing the problem.
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Basically yes. The bay has three sides at an angle to each other. There is a separate window on each side, joined together across the top by the frame and the windowsillat the bottom, with frame up the sides. Where the side and cenreal windows meet at an angle of about 120 degrees there are two strips of flat wooden beading (if that's the right word) about 1 inch wide and about 3 mm thick. Where the two strips meet should I imagine be a seal. As it is there is a minute gap which allows the draughts in. Behind the strips is a large gap before you get to the brick/stucco column which you can see from the outside. I want to fill the gap with insulation to stop the draught.

I hope that is clearer.

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