New sashes into existing window frames header

New Sashes into Existing Window Frames

New, Double Glazed, Timber Window Sashes Installed into Existing Window Frames

If your sash window or casement window frames Which? Trusted Traderare in good condition, we can replace just the moving parts of your timber window (the sashes), allowing for double glazing without replacing the window frame.

High Quality Performance

We purposely select materials that offer the highest quality performance and durability meaning that our windows are easy to use, secure and require minimal maintenance.  We are FSC® certified, meaning that the materials used in our windows are sustainably sourced.

What are sashes on a window?

Sashes are the parts of a window that move when you open or close the window. By installing new sashes into existing window frames, you can replace just the moving parts of the sash window or casement window without having to also replace the window frame.

This allows you to upgrade to more energy efficient windows.  Installing new sashes, rather than installing complete new windows, also helps save you money, minimises disruption and helps you retain the heritage of your home.

new sashes installation
Bespoke double glazed windows London


We have extensive experience installing new sashes into the existing box frames for both timber sash windows and casement windows.

When replacing the moving parts of the window, a high level of attention to detail is required in order to ensure that the new sashes fit and operate smoothly. This means that an exceptional level of attention to detail is required when measuring for the replacement sashes, before they are manufactured to fit precisely.

At The Sash Window Workshop, we will always take great care ensuring your existing windows are matched exactly and retain the original style of your home.

Energy Efficiency at a Fraction of the Cost

By replacing just the sashes (moving parts) of the window you can upgrade to all the benefits of double glazing without having to replace the whole window, helping to keep down the cost.

During the installation process, the old sashes are removed, before the new sashes are carefully hung in their place.

For most clients, the new sashes we fit to existing window frames are specified to be double glazed, unless single glazed is expressly required. We offer a range of glazing and paint finish options for your new sashes.

During installation, your windows are draught sealed to help keep your home warm and further improve energy efficiency and soundproofing.

Finally, new ironmongery is fitted to your windows.

New Double Glazed Casement Sashes

Below is a quick walk through of The Sash Window Workshop installing new timber sliding sashes into existing window frames

Accoya: Sustainable, Anti-Rot Timber Windows

For new sashes we recommend using a timber called Accoya, which comes with a 50 year anti-rot guarantee.  Accoya is a sustainably sourced, highly durable and stable wood.

As the installation of new sashes into the existing window frame does not go back to the brickwork, FENSA deem this work as repair work, rather than replacement. This means that a FENSA certificate is not required for this work.

We also manufacture and install complete new sash windows and casement windows, alongside offering a draught proofing service for timber windows.

Below shows a bay sash window where we installed new
sashes into the existing window frames


before work


during work


new sashes installed

Unsure what type of windows you have? Sash windows slide up and/or down to open, whereas casement windows open on hinges, like a door.



Accoya Anti-Rot




Double Glazing




Draught Proof

*Maximum Guarantees Shown. Please see our Guarantee and Maintenance documents for further information.