Traditional timber sliding sash windows are fitted into a reveal or recess in the brick work, both the sides & across the head (top of the window). There is NO recess at the bottom of the window, the hardwood sills are designed to sit on a flat surface.

When ordering a timber sash window, you will need the total window size so it is important to take into account the amount of window sitting hidden behind the reveal. We would recommend exposing approximately 30mm of the outer lining of the sash box on the top, left and right sides:

IMPORTANT – Check the internal width and height are larger than the external. It is also advisable to expose the overall size of the window by removing the internal architraves or linings, this can be a reassuring way to ensure that the windows are the correct size.

Sliding sash windows sitting in a standard opening.

New build properties tend not to have a brick recess for sliding sash windows, this is because they are designed to take spiral balance sash windows which can be fitted in a more conventional way, so the usual tight brick to brick measurement less 10mm clearance is the way to go with this. Traditional timber sash windows can also be fitted in a flush opening without a sash reveal, this is usually known as ‘brick to brick fitting’. When fitted brick to brick the outside facing side of a sash box can be ‘dressed’ with some trim if you feel this is required.

Should you require any further assistance in measuring sliding sash windows or any other type of window, please do not hesitate in contacting one of us. Why not send us a few photos of your windows and we’ll talk you through it!