Sash Windows: how they work and why they’re an important part of London

For many period homeowners, installing the latest uPVC sash windows are an is becoming an absolute must. Older, more elegant buildings are often fitted with windows that look aesthetically very pleasing, and so homeowners are often keen to restore them where possible.

Nowadays, it’s possible to buy modern sash windows that are completely double glazed, so you don’t have to sacrifice comfort for beauty.

If you have recently purchased a property in London or are considering a building with original sash windows, then here are some considerations for your purchase.

Traditional sash windows

Technically-speaking, it’s not just sash windows that are composed of two sashes. The sash is the glass pane and frame, and so the name derives from the fact that these windows open with a sliding sash.

Traditional Sash Window

This sash is moved by pulley mechanisms so you can lift it up and down when you need some fresh air. As you might imagine, this meant that it was hard to fit locks on many old versions, but the modern versions now come with a locking system (and older versions can be retrofitted with locks).

Traditional London homes

London is composed of many different generations of buildings, and those with sash windows are often from the Victorian and Georgian eras.

You will often see them in tall elegant townhouses, particularly in the South West area, or in renowned areas such as Islington.

This is why so many London property owners are keen to keep sash windows in place or find identical replicas.

Whether you should replace the sash window with a modern, plastic-based frame really depends on who you ask. Some would argue that this should never be done: arguing that it will ruin the original charm of the building and remove classic features.

Others, meanwhile, would debate that so long as it is in keeping with the original aesthetic of the home, it doesn’t really matter.

It is possible that you may need to ask for planning permission before you replace your windows. In this instance, you may have to repair them instead of replacing them in the absence of planning permission. However, you won’t know this without talking to your local authorities.


Generally speaking, sash’s are a huge appeal for many prospective homeowners in London. For many, the Victorian, Dickensian image of London is that of tall townhouses with beautiful and elegant sash windows.

It’s therefore in your interest to replace them in a way that is sympathetic to the original style if you do intend to replace them with modern versions.

You may have heard plenty of period property owners waxing lyrical about the original beauty of sash windows.

However, you might be slightly thrown off by the insistence that they should be repaired and not replaced — the best way to get reliable advice to contact an installer for advice as to what to do. You may also need to contact your local authorities to enquire about building permission in your area of London.