sash window

Wooden windows are loved for their classic and elegant appearance making them a great match for traditional, period homes. However, they are often seen as less energy efficient than their uPVC competitors. As professional joiners, we can tell you this is not the case. Wood windows can be energy efficient for several reasons which we will cover in this article, including how to measure the energy efficiency of your wooden windows and how to improve on your score.


Wood is a natural insulator. It has a lower thermal conductivity compared to materials like aluminium, which means it doesn’t easily transfer heat or cold. This helps in maintaining a more stable indoor temperature, reducing the need for heating or cooling systems.

Natural R-value

R-value measures a material’s resistance to heat transfer. Wood naturally has a higher R-value compared to materials like aluminium or vinyl. This means wood windows are better at resisting heat flow and keeping the indoor environment comfortable.

Low thermal expansion

Wood expands and contracts less with temperature changes compared to materials like vinyl. This reduces the risk of gaps forming around the window frame, which could lead to drafts and heat loss.

Sealing and weatherstripping

Wood windows can be designed and fitted with effective weatherstripping and sealing materials to prevent drafts and air leakage. Proper sealing is crucial for maintaining energy efficiency.

Double or triple glazing

Wood windows are often designed to accommodate double or even triple glazing. Multiple layers of glass with insulating air or gas layers in between enhance the window’s energy efficiency by further reducing heat transfer.


Wood windows can be custom-made to fit the specific dimensions of a building, minimising gaps and ensuring a tight fit. Proper installation is essential for energy efficiency.

Renewable material

Wood is a renewable resource, which makes it an environmentally friendly choice. Responsible forestry practices ensure a steady supply of wood for window manufacturing.


Wood windows are often considered more aesthetically pleasing, and they can add value to a home. This encourages homeowners to invest in maintaining and upgrading their windows, which can include energy-efficient features.

How to measure the energy efficiency of wooden windows

There are generally two options here:

  1. U-values – measure how effective an insulator a material is, and therefore, how successful it is at reducing heat loss. Some manufacturers quote the U-value of the whole window, whereas others quote the heat loss through the glass alone.
  2. Window Energy Ratings (WERs) – this rating system is based on a scale of G to A+, with A+ windows being the most energy-efficient. With this system, a window’s rating is determined by a formula that considers the total solar heat transmittance of the glass (the ‘g’ value), the U-value of the whole window and air infiltration through the window seals.

How to make wooden windows more energy efficient

It’s important to note that not all wood windows are equally energy efficient. The quality of the wood, the design, the construction, and the installation all play a significant role in determining how energy efficient a wood window will be. As professional joiners, with many years of experience under our belts, we are committed to using quality products and exemplary construction methods.  We go to great lengths in joinery preservation and all our wood is sustainably sourced. We are committed to reducing, reusing, and recycling where possible. Learn more about our wood, preservation finishes, and commitment to sustainability here.

Regular maintenance is also crucial. We provide detailed guidance on how to maintain our custom-made joinery to ensure that the windows continue to perform well over time.

With regards to glazing, we can go one step further than double or triple-glazing. We are approved installers of Fineo vacuum insulated glass. A premium glazing solution that offers grater thermal capabilities than triple glazing, but with the profile slimmer than single glazing. It is this slim profile that makes it a great (planning approved) glazing choice for listed properties and areas of conservation. Vacuum insulated glass is the ultimate in energy-efficiency for windows boasting a U-value of just 0.7 (A++ standard).

If you would like to find out more about the energy efficiency of wood windows, our team are extremely knowledgeable and would love to help 01273 814870.