Wooden windows for slackers

In its quest for a low-maintenance wood, American giant Andersen Windows finally found the answer to PVC-U discarded on the floor of its huge Minnesota factory. "We produce a hell of a lot of sawdust," explains a wry Jim Lawrie, CEO of Black Millwork, Andersen's British distributor. Before it hit on the idea of combining wood waste with a thermoplastic polymer to create Fibrex, the world's biggest maker of wooden doors and windows just fed its sawdust and wood shavings into the boilers – its own and those of a nearby prison.

Lawrie has now started importing Fibrex-based sash windows into the UK. The windows have the strength, thermal performance and look of wood. More importantly, like their PVC-U rivals, the windows simply don't decay.

Fibrex is a mix of pinewood sawdust and shavings – getting the right proportion of grades of waste is crucial, says Lawrie – bound together with a polymer. Coated with polymer, the wood fibre resists flaking, blistering, peeling, cracking and corrosion, and so doesn't need painting or regular maintenance. And as the wood fibre gives a greater rigidity and strength than PVC-U, Fibrex windows can support glazing with a slender frame that doesn't require metal reinforcement.

"PVC-U, wood and aluminium all have weaknesses," says Lawrie. "Aluminium's got a limited thermal capacity and a very flat section, so the aesthetics aren't ideal. PVC-U doesn't look traditional because it has thick sections reinforced with metal to compensate for its lack of strength. And wood is not low maintenance."

In other words, people prefer wood, but prefer low-maintenance exteriors even more. Fibrex, though, hits all the right buttons and has no Achilles heel. According to Lawrie, you can see it's not wood when you're close-up, but from 20 feet away you can't. And whereas the quality of wood can be unpredictable, Fibrex is a consistent, extrudable material, which simplifies manufacture.

The Fibrex windows available in the UK are the Woodwright range of sash models. Only the sash is made is Fibrex; the sash frame is wood protected by a 1mm layer of PVC-U on the external side. Woodright windows cost the same as PVC-U equivalents, although that may change given Lawrie's determination to grow the UK business by a steady 25% a year. To keep delivering that target, he's prepared to drop and raise prices to stimulate and choke off demand. "I don't want to grow faster than 25%," he says. "Otherwise you lose control of your business."

With Fibrex sashes first appearing in the US in the 80s, what's taken Lawrie so long to bring them over here? "I wanted the US to sort all the snags out," he explains. "You can do something in the lab and it looks good, but you never really know how it's going to perform till it's in the field."

Having served its time in the US, the material is finally out in the UK.