Replacing timber windows in heritage buildings: The Sash Window Workshop’s top tips

Deciding on the windows is an important part of a building project. The decision not only affects the look of the property but also affects the thermal efficiency, says Richard Dollar, Managing Director at The Sash Window Workshop.

Richard Dollar

Managing Director at The Sash Window Workshop

Do you need to replace the whole window?

Firstly, check if the frame is in good condition. If only the moving parts of the window are in a bad condition, you may be able to install new sashes into the existing window frames. This allows you to upgrade the window to double glazing without having to replace the frame.

Deciding on the right style

If you are planning an extension or refurbishment to an existing period property, high attention to detail is required to ensure that the property’s character is not lost.

Make sure that the new windows are in the same style as the original windows. This means checking various specifications. For example, for sash windows, make sure that they have the same designs for any sash horns, moulding, glazing bars and finish.

Is the building listed or in an article 4 conservation area?

If the building is listed or in an article 4 conservation area, planning permission will be required to make changes to the windows. Double glazing may be permitted, but you may be required to use heritage double glazing, which uses a slim profile double glazed unit, as opposed to standard double glazing.

Material choice

Traditional properties often suit timber windows as they are more period-appropriate. When maintained and painted properly, timber windows can last for over 100 years.

High-quality timber windows can offer great durability and energy efficiency.

However, not all timber offers the same longevity. When choosing a timber, check its durability and stability. Accoya is a popular choice as it is extremely durable, has high stability and comes with a 50-year anti-rot guarantee.

Glass options

When choosing the type of glass, consider what the room will be used for. For example, a bathroom window will often want a smaller window with privacy glass, stopping passers-by from seeing into the property.

In contrast, a living room or kitchen may suit a window with clear glass, allowing the occupant to look out onto the garden.

Choosing a supplier

Check that the supplier has experience working on similar projects and that installers are registered with FENSA.

Ask about U-values and check that new windows are draught-proofed on installation. This will allow you to check how energy-efficient new windows will be.

Check the company’s accreditations. Look out for whether they are members of the British Woodworking Federation or the SafeContractor scheme – if they are working on your site, it is important to ensure that they undergo the necessary health and safety training.

Finally, it is also important to check and query their guarantees – they should be able to tell you exactly what is and isn’t covered by each of the guarantees; no individual guarantee will cover everything.

Share this article

Login to post comments

About us

Future Constructor & Architect is a specification platform for architects and building contractors, which focuses on top-end domestic and commercial developments.

As well as timely industry comment and legislation updates, the magazine covers recent projects and reviews the latest sustainable building products on the market. Subscribe here.

Privacy policy

Latest updates


Sign up below to receive monthly construction, architecture and product updates from FC&A via email: