Timber windows offer a unique combination of aesthetic versatility, sustainability, and long-term performance, making them a compelling choice. Advancements in manufacturing, materials, and glazing technology have additionally broadened the design possibilities.  In turn these have enhanced the energy efficiency of modern timber windows. Here we’ll look at the specifics of timber window construction, focusing on their thermal performance characteristics and provide you with the essential information for specifying high-quality energy efficient timber windows.

Understanding Timber Window Construction

Each element of window construction is carefully examined to ensure that it is of the most efficient.  Key components include:

• Timber Frame: The structural element, which is available in various wood species, for example, a hardwood like utile mahogany, or an acetylated softwood like Accoya. The timber is chosen for it’s durability, stability, and aesthetic qualities. It is important to consider the location of the windows and the property itself, in relation to prevailing weather conditions that can affect it’s performance. Beware of choosing an inferior and perhaps cheaper timber, that might not have the longevity, durability and strength to perform the task.
• Glazing: There are many glazing options on the market today. Old windows in protected structures that have original glass, are obliged to maintain it. Newer windows, or those not in protected areas can avail of double glazing, incorporating low-E (low-emissivity) coatings to minimize heat transfer. The gap between the panes is filled with an inert gas (often argon or krypton) to further reduce heat conduction. Warm edge spacers minimize thermal bridging at the edge of the glass. There is acoustic rated glass for locations where noise is a problem. Additionally various films assist with protecting the furniture and interiors. This adaptability allows you to meet diverse performance specifications and optimise thermal efficiency for various project requirements. The synergy between advancements in timber technology and glazing technology ensures that timber windows can achieve the highest levels of performance.
• Draughtproofing: High-quality seals are crucial for preventing air leakage and water ingress, significantly impacting thermal performance. Not only the seal itself is important, but the exact location of the seal in the window is vital, otherwise the air will find a way to flow. Modern polyurethane foam seals work much better than brush seals and have excellent durability. Even when a window is closed for a long time, they will maintain their elasticity and form.
• Ironmongery: High-quality ironmongery ensures smooth operation and secure locking mechanisms. There are important considerations for building regulations as well as functionality, for example, fire egress restrictors are standard in sash windows on the upper levels and bedrooms. Ironmongery is available in a huge range of finishes and styles. Again consider the location of the property, as there are specific ranges for coastal locations and more.

Design Versatility

Modern timber windows are available in a vast array of designs and opening mechanisms, amongst them, tilt and turn, casement, hopper, and sliding sash. Sizes range from small, intricate panes to large, contemporary fixed designs. This flexibility allows you to specify windows that seamlessly integrate with virtually any architectural style, from traditional to contemporary. The dramatic improvements in durability, quality, and design over recent years have further solidified timber’s position as a sought after window material.

Thermal Performance of Timber Windows

Timber itself is a natural insulator. Modern timber windows, combined with high-performance glazing and effective draught sealing, achieve excellent thermal performance.

Thermal performance is quantified using several key metrics.

• U-value (or Uw-value): This measures the overall heat transfer through the window (frame and glazing combined). A lower U-value indicates better insulation.
• g-value (or SHGC – Solar Heat Gain Coefficient): This measures the fraction of solar radiation that passes through the window and into the building. A higher g-value allows more solar heat gain, which can be beneficial in colder climates but may lead to overheating in warmer climates. Optimizing the g-value depends on the building’s orientation and climate.
• Window Energy Rating (WER): This combines U-value and g-value to provide a single rating that reflects the overall energy performance of the window. WER ratings are typically expressed on a scale from A+ (most energy-efficient) to G (least energy-efficient) – like the BER ratings of the property.

Heat Loss Through Windows

The amount of heat lost through a window is directly proportional to its U-value, the area of the window, and the temperature difference between the inside and outside.

How to minimise heat loss?

You can minimise heat loss through windows by

• Specifying high-performance timber windows suitable for the climate.
• Optimisation and shading Maximise solar gain in winter and minimise it in summer.
• Using appropriate glazing
• Ensuring airtight installation Proper installation is crucial to prevent air leakage and thermal bridging.
• Considering window frame materials Timber offers excellent thermal performance compared to some other frame materials.

Cost Considerations

While the initial cost of timber windows may be higher than uPVC, their “whole-life” cost often proves lower. Much of the popularity of uPVC windows has come from marketing them as low maintenance which may not often be the case.

Durability and Maintenance

Durability has been a key area of focus and improvement in timber window technology. While no window is entirely maintenance-free, properly maintained timber windows offer exceptional longevity. Factory-applied spray coatings provide superior protection and extend the lifespan of the window.

Sustainability

Timber is the only truly sustainable construction material due to its renewability. Specify timber from sustainably managed forests certified by organizations like the FSC or PEFC.

About Us

Timeless Sash Windows is a timber joinery based in Ireland and working across Ireland and the UK. We manufacture new timber windows and refurbish historic windows. Our facilities and team can handle both large and small projects on a commercial and private property basis.