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This is far thicker than the sash window frame would have been when it was originally made, and can look out of place in a period property.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

Our windows and doors are handmade to order and have been approved for listed and conservation properties in over 30 planning authorities throughout London and the South East.

Not only do we sensitively replicate the existing period design of your windows down to the finest details, we also include understated features that upgrade the performance of your windows, including slimline double glazing that looks just like single glazing, specialist glazing options such as acoustic glass for improved sound insulation, and multi-point locking on casement windows to provide additional security.

If the frames are good enough to be saved, we can also replace the sashes or casements and fit them to the existing frames, to retain as much of the original architecture as possible while improving the performance of the window. We also offer a full range of repair and draught proofing services. 

To find out more about the options available, please get in touch to get a free quote or to visit our workshop and showroom. Our range of products includes bespoke timber sash windows, casement windows, front doors, French doors, bifold doors and fire doors.