Over the last decade or so, the timber window industry in the UK has been working hard to overcome the poor reputation of late 20th century wood windows, many of which needed replacing within 10 or 15 years, even with repeated re-decoration. Today’s high performance timber frames can be expected to last around 60 years – a lifetime or more for many people. We all know buildings with original timber windows that date back to Edwardian or even Victorian days, but how do we achieve that sort of longevity now?
It starts with the quality of the timber. Slow-growth pine, harvested from sustainably managed forests in northern areas of Europe, such as northern Sweden, is the typical substrate, used because it’s strong and well-suited to preservative treatment. Sometimes hardwoods are used, and so-called modified softwoods, such as Accoya™ are increasingly popular. The pine is engineered to remove defects, such as knots, laminated in layers to provide stability, and preservative-treated.
Design is important too. Windows need to be wind and water proof, but they also need to shed water efficiently and allow good paint adhesion. That means paying attention to sloping angles and curved edges.
The manufacturing process is crucial. Full factory-finishing allows precise coating coverage in factory-controlled conditions. Special attention is paid to sealing end-grain and joints.
But there are always weak spots in any design. In windows one of the most vulnerable parts of the window is the glazing beads – fine, machined profiles fully exposed to weathering.
It was to overcome this weakness that development of Qwood window and door beads and bars began in 2003/4, with the first windows using the bars coming to market some five years later.
Because they are a wood composite rather than just wood, they provide the appearance of timber with none of the drawbacks. They offer the advantages of improved fabricating performance and design (real reductions in time and material waste) with good coating performance and zero long-term maintenance.
Today, as the market for real wood windows looks increasingly healthy, most major UK timber window manufacturers use Qwood beads to help extend the life of their windows.