Traditional material, modern solution
In the Kansai region of Japan, there is a temple complex called Horyuji. Many of the buildings within this complex have stood for more than 1 200 years, with the oldest of all these structures being a five-storey pagoda and main hall dating back to 600AD.
These buildings have survived centuries of weather, feudal wars and even a fire in 700AD. But what makes them even more remarkable, is that they are made almost entirely from wood.
Wood is not what it used to be
There is evidence of wood being used in construction dating back over 10 000 years, making it the longest-serving material still in everyday use.
Over the past few decades, the quality and engineering of wood has undergone a revolution, and it’s increasingly being re-evaluated as a modern-day first choice for both structural, interior and exterior applications across domestic and commercial projects. Progressive manufacturing techniques and specialist coatings are making it even more versatile, durable, and efficient.
From natural hardwoods and engineered softwoods, plywood and chipboard, to glued laminated beams (glulam) and cross-laminated timber (CLT), wood offers unique properties which are all underpinned by the material’s inherent health and wellbeing benefits, and its sustainable and physical characteristics.
Engineered to be more than just wood
The broad term ‘timber’ encompasses a wide variety of species, all of which possess different performance characteristics. Over the past decade, a number of engineered and modified timber products have been developed to provide solutions for situations where conventional timber would not always be viable. Both engineered timber and modified timber have been developed to provide enhanced strength, durability, and stability.
Engineered Timber
TRADA (The Timber Research and Development Association) define engineered wood products as those that ‘are made from wood sections which have had the weaker areas, such as knots, removed before being glued back together, resulting in a stiffer and stronger product.’(A)
(A) TRADA Factsheet – Engineered Wood Products
Modified Timber
There are a number of brands of timber that are available that have been either modified chemically or by heat treatment. Examples include Accoya® and Thermowood®. Engineered timber and modified timber are increasingly being recognised by the construction supply chain as offering a genuine alternative to PVCu, steel and aluminium.
Image: Accoya® 2019
Building for sustainability and longevity
Engineered softwood is commonly specified for both domestic and commercial projects because it offers good-value and is seen as a solution to many of the current challenges to sustainability and waste management thanks to its:
- Natural abundance
- Renewability, recyclability and reusability
- Ability to absorb carbon emissions
- Flexibility and high-tensile strength
Building for sustainability and longevity
If we take window frames as an example, hardwoods used to be the material of choice as they are usually denser than softwood, however, modern technological advances have brought engineered softwoods, such as Redwoods – i.e. Scandinavian Pine and Siberian Larch – very much to the fore. The advent of these technological improvements has meant that engineered softwood is now generally the material of choice, being free of knots and imperfections – enhancing stability and the lifespan of window frames.
Building for sustainability and longevity
The Wood Window Alliance works with the industry and advocates the use of engineered softwoods, quality hardwoods, and modified timber. The choice of which type of timber specified will be driven by the desired finish and budget rather than the material, as modern manufacturing techniques enable the overall product performance (longevity and durability) to be very similar.
Research insight
An independent study by Heriot Watt University (B) has found that a typical casement wood window frame made to a specification set by the WWA can last to and beyond 60 years in average climate conditions. In the same study, PVCu windows were found to have an estimated life cycle of up to 35 years.
(B) Reference – Whole Life Analysis of timber, modified timber and aluminium-clad timber windows: Service Life Planning (SLP), Whole Life Costing (WLC) and Life Cycle Assessment (LCA), Dr Gillian F. Menzies, Institute for Building and Urban Design, Heriot Watt University, June 2013
The use of timber in commercial projects
When specifying any material, there are considerations that need to be addressed and this can also be said for wood in commercial spaces. Many factors will be specific either to the building itself, the timeline of the project or whether it is desired that a particular sustainability standard is achieved.
For example, wood flooring is ideal for many commercial environments and can be used in conjunction with a concrete, steel or timber structural base. However, awareness and correct specification of uniquely engineered timbers is needed when accreditations, such as BREEAM, are desired.
A focus on timber windows
When considering specifying windows and doors, alongside the regulatory requirements associated with their use, other characteristics of wood windows and doors need to be considered. These include:
- Weather resistance
- Thermal and acoustic insulation
- Heat and light transmission
- Operating forces
- Long-term durability
- Security
A focus on timber windows: maintenance
An important consideration of any product specification is its ongoing maintenance requirements. All windows and doors require maintenance regardless of the material from which they are made.
For example, the surfaces of the glazing and frame need regular cleaning and hardware requires lubrication. Within their service life, many will also require re-glazing and seals may need to be replaced, so it’s important that all windows and doors are periodically checked for any damage or wear.
For wood windows and doors, should any minor defects in the coating be detected during the inspection these can be simply retouched with a spot repair. This means that only a renovation coating needs to be applied to maintain the coating’s sheen, colour, and durability, which effectively prevents the need for full redecoration.
Research (1)
A clear demonstration of the longevity of timber products is the results from a recent trial at the Building Research Establishment (BRE), which involved BWF member Stora Enso Timber UK.
The findings show that wood windows made from untreated hardwood redwood (pinus sylvestris) with a water-based acrylic coating have remained in excellent condition after 14 years of south-facing exposure with no intermediate maintenance, and will need only a simple refurbishment coat to extend their serviceability further.
Research (2)
This trial echoes the findings from the independent study into the longevity of wood window frames made to the Wood Window Alliance (WWA) specification.
With normal maintenance, it was found that a typical factory-finished wood window frame made to WWA standards can be expected to last up to and beyond 60 years – providing exceptional value for money over their lifetime. That is double that of a PVCu equivalent.
Want to learn more?
We hope you’ve found this module useful. If you would like to keep learning, click on one of the suggested modules or visit the Wood Windows Alliance website to see how one of our members can help you on your next project.
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