Modern timber windows and doors are a specifier’s dream, combining technology, performance, sustainability, and beauty.

Knot-free timber, often engineered or modified, factory finishing with microporous paints, factory glazing, gas-filled glazing, enhanced security, energy ratings, performance and paint guarantees, and quality assurance and certification schemes all make timber windows sophisticated products that are fit for purpose. Add to all this the backing of environmental groups such as WWF and Greenpeace, and specifying timber windows and doors is a no-brainer.

“The arguments for specifying wood windows just keep on stacking up,” said British Woodworking Federation (BWF) chief executive Richard Lambert. “Most specifiers know that they have A or A+ ratings in the Green Guide, that wood is the most thermally-efficient framing material and that housebuyers and tenants like the aesthetic appearance. Now independent research has found that windows manufactured to Wood Window Alliance (WWA) standards last longer, with a service life of at least 60 years (see p30). This transforms the whole life cost calculation. It’s also been proved that WWA frames are carbon negative over their life cycle.

“There’s no better way of ensuring long-term value, a lower carbon footprint and a more attractive building than specifying wood windows.”

JCK Joinery in Leicester is just one of the many UK manufacturers that has adopted a belt and braces approach. A member of the BWF, JCK uses FSC and PEFC-certified softwood and hardwoods to produce sash and casement windows with square, semi-circular, elliptical or gothic arch heads and multi-point locking.

Its wide range of doors, from fire doors to internal doors, access control doors and external doors, are available with Secured by Design accreditation, the stamp of approval from the Association of Chief Police Officers’ security scheme.

JCK is also among the growing number of joiners using Accoya modified wood. The product is softwood which, through an acetylation process, takes on the properties of hardwood to produce some impressive performance attributes. In above ground applications Accoya will last at least 50 years, shrinkage and swelling is reduced, and paints and varnishes last three to four times longer.

Thermal performance is a big selling point for timber windows and many manufacturers can now boost super low U-values for their products. George Barnsdale & Sons was the first UK company to produce a BFRC A-rated timber window with its stormproof casement, while JELD-WEN claims that its DreamVu window breaks new ground as a volume manufactured product with some of the lowest U-values in the UK. Manufactured from FSC-certified engineered timber, the DreamVu has a U-value of 0.7-2.0W/m²K and the company says it can help achieve the higher levels of the Code for Sustainable Homes. Even before its official launch last year it had been specified for a UK Antarctic Heritage Trust project on the Antarctic Peninsula.

JELD-WEN says the slim profile and flush sash design will suit any dwelling type and it can supply a product that will fit most architects’ requirements. The windows carry a 30-year guarantee on the timber and a 10-year guarantee on the paint finish. The exterior can also be clad in powder-coated aluminium which again is guaranteed for 30 years. A range of doorsets, both in timber and aluminium-clad timber complements the windows.

Passive Windows also claimed a UK first with the launch last year of the first timber outward-opening passive window which meets the requirements of Germany’s Passivehaus Institute. The windows, made from PEFC or FSC-certified timber have a whole window U-value of 0.8W/m²K and can be aluminium clad.

Among its designs Passive Windows also produces an alternative to the conventional outward opening window – the “open out parallel” where the window opens completely from the frame but is hinged on three sides to combine maximum air flow with safety benefits.

NorDan, whose UK contracts range from housing to schools and commercial properties, produces low energy windows: NTech 0.7 and NTech 1.2. The former is a triple-glazed unit with insulation incorporated into the timber frame. The NTech 1.2 is double glazed and achieves a whole window U-value of 1.2 without using insulation in the construction.

At WWA member Clifton Joinery, windows are made from solid timber – generally idigbo when a paint finish is specified and European oak, among other species, for a clear finish. The company’s Teknos finishes carry a 10-year guarantee. The same species are used for its doors, ranging from entrance, internal and bifold doors, to stable doors, but many other – certified – species are available. “We have manufactured doors in American black walnut – a stunning timber,” said the company.

The Kitemarked company supplies high-end contracts throughout the UK. Its biggest project outside London was £300,000 of windows for a 700-acre Henley estate.

In making high quality, high performance joinery Clifton pays attention to every detail, so when making doors, it won’t forget pets. “We even make special openings for cat flaps,” the company said.

NorDan produces two low energy windows - the NTech 0.7 and NTech 1.2

Conservation innovation

Essex joinery manufacturer Mumford & Wood (M&W) had to satisfy strict design criteria set out by planners and architects when it supplied its Conservation windows to the refurbishment of a property in Chelsea, London.

The mixed use development of housing, retail units and offices required the company to adapt its sash and casement windows and doorsets to match the original fenestration.

The extensive structural refurbishment of the building involved the retention of the facades although the property was underpinned and the existing basement slab removed, replaced and lowered.

“This was not a one-size-fits-all project by any means,” said managing director Simon Howard. “Our Conservation box frame sliding sashes, casements, fanlights and doorsets had to replicate the original frames. It involved intricate design input from us and adaptation of our standard product.”

Ground floor box frame windows required special, large meeting rails with a detailed mould fitted to the face; casements had special external feature moulding to the frame and casement fanlights had a special bar pattern.

“The large stair frame, over 7m high, was designed with a contemporary feel. The architects were very stringent on the detail of this window and we worked closely with them to achieve their vision,” said Howard.

M&W’s Conservation range is manufactured from engineered clear grade larch and the windows have BFRC energy ratings from A to C, depending on specification, and carry Secured by Design, Energy Trust and BSI Kitemark accreditation.

Solar gains for glazing

Nanotechnology could allow solar cells to be sprayed onto window panes.

Windows and buildings could be turned into large-scale energy generators within the next five years thanks to new thin film solar cell technology.

Norwegian company EnSol AS has patented the thin film solar cell technology and is working with the University of Leicester’s Department of Physics and Astronomy to develop a solar cell material that could be coated as a thin film on, for example, windows.

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