Sash Window Sill Replacement

bay sash windowSash Window Sill Replacement by Ventrolla (After)


Sash window sill replacement or repairs are one of the most common problem areas on timber sash windows. External sills, in particular, bear the brunt of the British weather – and when wood becomes exposed due to cracked or flaking paintwork, rainwater is easily absorbed. And that’s when rot can set in.



Repairing a rotten sill, however, is not as easy as simply replacing the timber. Affixing new timber to a vulnerable sill corner will leave you with the potential for the same problem to happen again. Sill repair is a complex job that requires the expertise of specialists, like the team at Ventrolla.

So, what method do we use to do the job thoroughly?

Let’s take a look at Ventrolla’s sash window sill & lower box assembly:

  1. Rather than simply cutting off the ‘nose’ of the sill, we completely remove the sill and the bottom of the box to around 300mm up the frame.
before sash window repairVentrolla’s Sash Window Sill & Lower Box Assembly: The bottom of the box is removed along with the rotten sill


2. We replace everything we remove with new timber so all joints are new, sturdy and solid.

3. New joints are sealed to prevent water ingress, and because they are higher up the frame, they are less susceptible to future problems caused by water running down and pooling.

4. We install a new sill made from Sapele hardwood, profiling it to match the existing style of your original sash window.

during sash window repairA new sill is installed to replace the rotten sill.

FACT: By replacing the lower box frame as well as the sill, we retain the strength and structural integrity of the entire sash box. Removing the bottom of the box also ensures that any rot in the outer cheeks or pulley stiles is also removed.

Which of my windows are most at risk?

Any timber windows, especially those that have been poorly maintained are vulnerable to sill damage. A common misconception is that north-facing windows are the worst affected because of the lack of sun. In fact, the opposite can be true. In general, south-facing windows are where early deterioration occurs due to sunlight cracking the paint, allowing moisture to penetrate the sill.

during sash window repairsBEFORE Ventrolla window sill replacement
after sash window repairAFTER Ventrolla window sill replacement

How can I avoid this from happening in the future?

Keeping on top of the maintenance and paintwork is the best way to protect your timber sash windows and sills. They include having a regular painting schedule, where you also keep an eye on the condition of the wood and act as soon as you see signs of rot. A survey from window experts can check this for you if you’re not sure.

If you are suffering from rotten sills and would like us to quote for repairs, or if would like your windows surveyed, don’t hesitate to contact us today.