Sash windows are a beautiful addition to any home, but with rising energy costs some homeowners may be concerned about their energy efficiency.

In this blog post, we’ll explore whether or not sash windows are energy efficient and provide some tips on how sash window restoration can make your property warmer.

sash windows at home
The thermal performance of wooden sash windows can often be poor if large gaps

So if you have recently purchased a house with sash windows or planning to renovate them in the coming years, stay tuned; you will find this article eye-opening, especially when paired with Composite front doors available here. And hopefully, the tips from this article with save you money for window replacement.

Inherent issues of original sash window design

Sash windows were invented in the 17th century and have some design features which make them inherently draughty.

The main issue is the way that the window opens – for the window to open, one of the sashes has to slide past the other. This leaves a small 3 mm gap between the two which can let in draughts, make sashes rattle and also let some dust in.

This gap also allows the warm air to escape from your property and the cold air to come in – making your home less energy efficient.

Another issue with older sash windows is single glazing, which has a very low U-value and is not effective that’s why we can say that original windows with single glazing are not efficient.

However, the very same traditional window design opens up the possibility of making your sash windows much more energy efficient by re-glazing them with thin-profile vacuum glazing and installing modern draught-proofing seals.

Condensation on the window glass panes

Another issue that homeowners of Listed buildings with single glazed windows can experience during cold mornings is condensation forming on the interior side of the glass pane. Some people collect this moisture with a window vacuum cleaner. Some people just leave it to dry by itself.

Are Sash Windows Energy Efficient?
Modern manufactured energy efficient sash windows give the old style look.

The internal condensation on the windows is not something positive as it gradually can damage the protective layer of paint and start the rotting process inside a wooden frame.

Modern sash windows

New bespoke sash windows, which are made to measure to replace the original windows, usually come double glazed and draught sealed.

However, due to the development of vacuum double glazing, which offers industry-leading 0.7 U-values in a 7 mm thickness glazing unit, the reglazing of existing single-glazed windows has become a more viable and cost-effective solution for period properties.

Timber windows are more energy efficient than UPVC replicates.

The most important thing to know when comparing timber windows and UPVC replicas is that the thermal efficiency of a window doesn’t only come down to the materials used.

In fact, the way in which the window is designed and manufactured will have a much bigger impact on its thermal efficiency than the materials it’s made from; however, generally speaking, UPVC sash window replicates are less energy efficient than the same window made using timber.

Restoration of original frames and glazing upgrade

As mentioned in previous sections, there are two ways you can make your sash windows more energy efficient.

The first option is to have your original window frames restored and draught-proofed, and the second option is to replace inefficient single glazing with vacuum-insulated double glazing.

The reglazing, together with frame renovation and draught-seals installation, is an excellent substitute for full window frame replacement or sash-only replacement and also has several advantages over the secondary glazing solution.

Turn your original sash windows to passive house grade windows

The request for passive house windows in terms of U-value is 0.8 W/(m²K) or lower.

With FINEO glass which has a U-value of 0.7 W/(m²K), you can have your traditional timber windows reglazed and make them match the modern standard of a passive house.

That’s why in our conclusion, we would say that sash windows design is very adaptable to modern needs and, with the right combination of skills, tools and materials, can be transformed into high-energy efficient windows which save thousands of pounds per year in energy bills but also look fantastic like traditional windows.

What type of windows are the most energy efficient?

There is two parts to this, as it depends on glass and frame. Obviously double or tripled glazed glass improve insulation and let less heat out.

The frames are also important though, wood is actually a better insulant than metal. But being natural and can swell and bow with moisture and rain which leaves gaps for cold air to flow in. Metal frames rarely have this issue and tend to be more energy efficient.