How to reduce heat loss from sash windows

Many timber windows in Scotland are in their second century. Modern plastic units may well end up in landfill after just 20 years.

Replacing traditional sash and case windows with double glazed units is very costly. The other energy efficiency measures listed here are far more cost-effective.

Replacing traditional windows with incompatible windows such as double glazed PVC units can harm the look and character of a building – especially if the style differs from the original. It can also cause long-term damage to window frames, creating additional costs.

From a conservation and sustainability perspective, existing window fabric should be retained and improved wherever possible. Sash and case windows are extremely durable and will last many decades if well maintained.

If you plan to make changes to your property, you might need consent.

It’s a criminal offence to:

• materially alter, extend or demolish a listed building or demolish a building in a conservation area without consent

• carry out unauthorised works, or allow unauthorised works to be carried out, to a scheduled monument

Find out more about consents

You can make your windows more energy efficient in a number of ways. Draught proofing is the most effective solution to keeping warmth trapped inside and should be your first goal.

Aim to keep windows in good repair in the first place – frames that have warped or no longer fit well will let in draughts. Close shutters and curtains at night to reduce heat loss. You can also consider adding secondary glazing, easily removable in warmer months.

This involves removing a small amount of the timber of the window frame and replacing this with tubing, brushes or small metal fins. Draught proofing creates a better seal when the window is shut – and often makes for easier opening too.

Draught proofing:

• reduces heat loss

• improves noise insulation

• helps to stop dust getting in

• is cheap and highly cost-effective

• doesn’t affect the look of sash windows

Windows with very slender frames may be weakened by adding draught proofing.

Some ventilation is good – both to reduce condensation and ensure the safety of open fires, stoves and gas appliances.

Use shutters if you have them – this is one of the best ways to reduce heat loss at night. Single glazing lets in more heat from the sun and shutters help to trap warmth inside overnight.

Timber shutters reduce heat loss by 51%.

Consider having ill-fitting shutters restored. If the original shutters have been removed, it’s possible to have new shutters made.

Heavy, lined curtains are a good alternative. These can reduce heat loss by 14%.

Adding secondary glazing to sash and case windows can help to reduce heat lost through the glass and through draughts.

Fitting secondary glazing involves attaching a second sheet of glass or acrylic to the inside of the window frame. Minimal changes are needed to the window fabric, and the glass panel can be easily removed. The character of the building from the outside is largely unaffected.

Secondary glazing:

• reduces heat loss

• can filter out some outside noise

• helps to stop dust getting in

• is a cost-effective solution, generally cheaper than double glazing

• doesn’t affect the look of sash windows

Installing secondary glazing can reduce heat loss by 63%, making it one of the most effective ways to improve thermal performance. Heat loss can be reduced by more than 75% when secondary glazing is used with other methods like blinds and shutters.

You can remove secondary glazing in the warmer months when it’s not needed.