March 3, 2025

In a survey conducted by the British Woodworking Federation (BWF) in 2023, 70% of 1,500 homeowners thought timber windows had a shorter lifespan than their counterparts, aluminium and uPVC. However, a study by Heriot Watt University suggested that timber windows have the ability to last decades longer than their counterparts, with a projected lifespan of 60 years for most if the appropriate steps are taken to help them last and depending on the exposure scenario they are in, such as weather conditions.

The robust nature of wood, combined with modern preservative treatments, allows timber windows to withstand the test of time, maintaining their structural integrity and design far longer than many synthetic alternatives.  

Although not all timber windows and doors are created equal and there are various factors that can influence the longevity of your timber window including material choice, manufacturing processes, correct installation, and maintenance. With a particular focus on manufacturing processes, we explore some of the key factors affecting the longevity of a timber window and door, and what you can do to prolong the lifespan of your timber windows.  

Monitoring Moisture Content

One key factor that affects timber’s long-term durability is whether it remains dry or not. If timber remains dry (usually deemed a moisture content of less than 20%) it will not become rotten. The acceptable moisture levels of timber depend on its final use and the average relative humidity of the environment it will be situated in.  

Microporous paint, regularly used for timber materials, is a type of coating designed to be permeable to moisture and air. The paint contains tiny pores and gaps that allow air and water vapor to pass through the paint and into a substrate beneath.  All micro-porous paint systems will absorb and release moisture depending on the time of year, and so the design of each window needs to allow for this to occur.  

Ideally, timber should be processed at around 12% moisture content as the moisture content in the UK oscillates between 12-16% depending on the weather and climate. Most timber used nowadays is engineered, which makes it more stable, and therefore easier for coatings to be applied and to be maintained. But, if you’re laminating timber, it needs to be around 12% moisture content. The ambient moisture content in a store and a heated factory will dramatically reduce this unless the atmosphere has the moisture controlled.  

Combining Design and Performance.

Design is about creating stunning windows that perform to the highest levels possible. Constantly developing timber products to ensure they perform to the highest standards possible ensures that the design of the window is optimised, whilst refining techniques that ensure the timber performs effectively.

To influence the design and performance of timber windows, you can concentrate on preventing water ingress by incorporating things like internal beading, which research has shown significantly extends the life of a timber window. You can also make small profile adjustments to ensure they discard water as easily as possible. The design and assembly of joints also influence the long-term performance of the paint finish as timber moves depending on temperature and humidity. If a joint fails, there needs to be a secondary line of defence. This can be achieved by carefully sealing all the unexposed joints, allowing them to be protected even if the joint fails. Consistently developing timber products can help understand any changes that need to be made to coatings to ensure they perform to the highest standards.

Having a thorough paint process.

To allow coatings to last for decades, there needs to be a very good bond between the coating system and the substrate. This cannot be achieved by spraying directly onto the substrate as the paint does not penetrate deeply enough. To ensure this doesn’t happen, a 2-coat flow coating system can be used which deluges the product and goes into a very high humidity area to stop the paint drying too quickly and to allow it to penetrate deep into the substrate. Any exposed end grain should then be sealed, and a special sealant applied to all V joints, allowing the joints to move without cracking the final coating.  

When choosing the paint or stain finish for your timber window, it is important to consider the fact that light stains are not as good as opaque finishes as they are not as efficient at blocking out UV light. This will affect the coating and the substrate. Also, dark colours, particularly windows fitted on the South or Southwest, will absorb a large amount of heat on a sunny day, which is more likely to cause the timber to move. 

Other considerations that impact the longevity of timber windows.

As well as wet conditions and the paint process affecting the condition and longevity of timber, other factors can affect its long-term performance. These include:

  • The position of the unit in relation to the building – this will alter the timber’s exposure to weather conditions. The further back the window is set in the opening, the more protection it will get.  
  • Extended timber cills – cills are the weakest part of the window, consider stone or other types of cill for a stronger structure.  

How can I ensure my timber windows will last?

As we have explored, a very well designed and manufactured timber window and door will stand the test of time with very little maintenance but to ensure your timber window lasts longer, simple inspection and maintenance will help reduce the likelihood of expensive maintenance in the future. 

There are various ways to maintain your timber window to ensure its longevity. For instance, it’s important to make sure there is no build-up of algae or moss-type organisms on your window as they can penetrate deep into the coating. This is more likely to occur on north-facing elevations. To prevent this from happening, you can use diluted household bleach on areas where algae may be starting to form. 

You should also check for cracks in your windows, particularly on joints. They are simple and cheap to rectify and will dramatically reduce the re-coating period if dealt with efficiently.  

It is important to choose the type of timber for your window wisely. We would recommend opting for an engineered timber, such as Accoya. The substrate in Accoya is more stable and the thermal performance is better. Accoya will also provide the best long-term paint performance, better than alternatives like Oak.

What makes a George Barnsdale window last a long time?

To ensure our products last longer, we have developed our premises and manufacturing techniques to ensure we can supply the highest quality products.  

To control the moisture content, our store and factory have an environmentally friendly humidity control system to ensure our products remain at an optimal moisture level whilst in the factory. When it comes to design, we were the first company to introduce internal beading of sashes in the early 1990s and we make small adjustments to profiles to ensure they discard water as early as possible. Our Traditional Box Sliding Sash windows used to encounter issues with the joint between the cills, jamb, and front lining. However, we have altered the design to rectify this issue, sealing all the connections in that area with a special sealant. This, as well as two flow coats that further penetrate any unseen areas, have radically changed the long-term performance of our windows. 

At George Barnsdale, we have spent decades researching and developing our timber windows to ensure they meet the highest industry standards. Our on-site R&D centre allows us to constantly innovate to perfect our paint systems using our own QUV accelerated test chamber and test our timber windows and doors against weather or security conditions. This extensive research allows us to develop our products and systems for optimum long-term performance. 

A great example of our long-lasting windows is the King’s Cross project we supplied timber windows for in 2003. We revisited the building 20 years later to find the windows still in great condition. Though some needed a good clean, it was evident that the timber and the paint finish were still perfectly intact, despite no recoating having taken place. This is a result of meticulous efforts taken to enhance the longevity of the windows, and the work we do at the manufacturing stage to create a long-lasting product. 

Timber, if manufactured with longevity in mind and maintained throughout its lifespan, will last for 60 years or more.  As a building material, timber provides many benefits that allow it to perform to the highest standards whilst providing the design flexibility to replicate even the most unique specifications. To find out more about how we manufacture, visit our website: How We Manufacture – George Barnsdale.