Bespoke box sash windows

Many standard design sash windows have thick frames, often up to 174mm thick.

This is far thicker than the sash window frame would have been when it was originally made, and can look out of place in a period property.

Making sure sash window frames are a perfect fit for your property is difficult when using thicker, cheaper double-glazing units, and is a detail that many timber window suppliers overlook.

But window manufacturers such as Timbawood offer a bespoke service rather than a standard product, and can match the depth of your original sash window frames while still exceeding building regulations for thermal efficiency.

Slim sash window frames – Why it matters

The images below show cross sections of sash window frames of varying thicknesses. (Click on images to enlarge).

Slimmer sash window frame (Cross-section)Thicker sash window frame (Cross-section)

Most period properties have an L shaped recess (check reveal) in the walls which the sash window frame sits in.

The thickness of the frame needs to match the depth of the recess (usually between 140mm and 150mm) in order for the frame to sit flush against the inside of the wall (see the cross-section above left, set at 145mm reveal depth with a 140mm frame depth).

If the sash frame is too thick, it will protrude into the room (see the cross-section above right, set at 145mm reveal depth with a 168mm frame depth).

This may not sound like much of a problem, but with a thicker frame and sashes the architrave will have to be packed out by up to 2 inches, which can look very bulky indeed.

On a splayed bay, due to the angles, the effect will look even worse.

Sash window quotes – What to ask for

When getting quotes for sash windows, make sure that you ask whether the frames will align flush with the inside of the walls.

It is details like this that will prove to you whether the window supplier offers a bespoke service, or a standard product. 

As specialists in windows and doors for period, conservation and listed properties, at Timbawood we can exact-match your current windows down to the finest detail. 

If you would like to speak to one of our experts, get a quote or arrange a free survey, please get in touch.