To clarify, sash window restoration refers to the process of replacing the sashes only and retaining the original box frame. Restoring sash windows can be an intricate task, but one that is very worthwhile. If the box frames of your sash windows are still in a repairable condition, restoring them and replacing them with double-glazing can be a more affordable option than replacing them, and it can also be less disruptive.

With proper care, restored windows can last for many years. In most cases, we can retrofit frames with standard double glazing, or we can retrofit with 0.7 W/m²K U-Value slim double glazing, which will make your sash windows as efficient as triple glazed new windows whilst retaining the slimness of a single pane. The new wooden sashes will also undergo full draught proofing.

Before we take a closer look at the sash window restoration process, take a moment to recap the components of a sash window. This will help you to fully understand our explanation of the process.

The general sash window restoration process at Parsons Joinery and our sister company Wandsworth Sash Windows is as follows:

Replacing the window sashes is our most popular service and involves fitting brand new fully painted wooden sashes into the existing box frames. The new wooden sashes will have double glazed/vacuum insulated glass and the service also included full draught proofing.

What is included in our sash window restoration service, step-by-step:


The old sashes are taken out. This is done carefully by removing the staff bead around the perimeter on the inside, allowing the old bottom sash to pop out.


Next, the parting bead is removed. This allows the fitter to remove the original top sash and the sash chords are cut.


The old steel weights housed in the original frames are removed.

So, at this stage, the old sashes have been completely removed but the existing frame remains in place.


The fitting team can then begin fitting the new sashes. All our sashes are handcrafted by our expert joiners in our UK-based workshops.


All windows are completely different. Some sashes may need to be planed on site to ensure they perfectly suit the original box frame.


New double-glazed sashes are much heavier than the old single-glazed sashes. We add lead into the old steel weight to counterbalance this weight. This is how the new sashes will slide up and down.


When the weights are inserted into the pockets of the existing box frames, the new wooden sashes can be hung into the old frames. They are hung on white nylon sash chords.


We install new parting and staff beads which further insulates the windows from draughts.


Your choice of ironmongery finishes off the windows.


The result? Brand new wooden double-glazed sashes expertly installed into the existing box frames.

View the full video of our sash restoration process here:

For more information on our sash window repair services please feel free to contact us.  We will be happy to chat through your requirements or provide an obligation-free quote.