Why do I have gaps between the Sash and Frame?

Sash windows need gaps around them to allow for thermal expansion during hot / cold weather and to reduce the force required to operate the locks. This gap is typically up to 3.5mm and is why the sashes are fitted with woolpile to accommodate these differences. Woolpile weather seals compress down, still sealing effectively, without increasing the friction, which could hinder the operation of the sash. Therefore, when a window is locked shut, with downward force, it is possible to compress the lower seal, exaggerating the gap at the head. This is normal, and once the force is removed, the sashes will centralise, correcting the gap at the head.

Why do my sashes move up and down when locked?

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