Window Frames: Timber or PVCu?

ABOVE: This Epwin PVCu casement imitates the look of small panes (epwin.co.uk).

The two main options for windows are timber (the traditional choice) or PVCu (a favourite in new homes since the 1990s and generally a little cheaper). Over the years, other materials have come to the fore: steel was popular in the 1930s, aluminium in the 1960s (both are still available but are now rarely used). PVCu first appeared in the 1960s; its popularity quickly spread and it now holds around three quarters of the market share.

PVCu is usually supplied white, but various foil facings are available which can simulate natural wood finishes to varying degrees of success. PVCu windows are invariably factory made and promise years of maintenance-free service, while timber windows require repainting or staining every few years. In the past, timber was also perceived to have a higher glazing failure rate, while PVCu double-glazed units rarely suffered this complaint. This is because they are fitted in a factory, which greatly reduces the likelihood of the units misting.

Even so, PVCu is not universally loved. Many people don’t like the fact that – with a few exceptions – they look plastic (which is what they are); others don’t like their perceived environmental impact.

The success of PVCu has caused the timber suppliers to have a major rethink, and today the majority of timber windows are also supplied factory glazed and pre-finished: this has effectively cured the problem of misting units, which tended to result from sloppy on-site glazing practices.

As such, most windows are accompanied by a long guarantee for both frames and the glazing units — so check these are in place.

Alternatives

Many suppliers now offer timber windows clad with an aluminium external casing. Some are simply metal claddings fixed over timber, others are more complex composites of half-timber, half-metal. Either way, they have the look and feel of timber internally, and a maintenance-free surface externally.

There is also a small but growing market for glass-fibre (or pultruded) windows. Popular in North America, glass fibre is available in any colour, is stiffer than PVCu, and has something of the look of timber while promising a maintenance-free exterior.

ABOVE: This classic timber sash window from Mumford and Wood is the perfect addition to a Georgian-style home (mumfordwood.com).

Hardwood, Softwood or Improved?

With timber windows, it used to be a choice between hardwood and softwood. Hardwood is generally longer lasting, but the longevity of any timber window really depends on how well it is maintained. If you are confident of being able to repaint every few years, then softwood windows will last for hundreds of years. In the past few years processes have been introduced which chemically improve softwood. Currently, such timber is being marketed under the Accoya® brand. Another option is to use a laminated oak, which gives the look and feel of that wonderful timber without the ensuing problems caused by its movements.

Imported or Home Grown?

Many self-builders buy imported windows. The quality is usually high and the prices can be keen, but watch out for the delivery lead times and the service offered by the UK distributors. Check what procedures are in place if the delivery is wrong, or parts get broken in transit. Also bear in mind that British house designers routinely use modular opening sizes. Neither North American nor Continental manufacturers make windows to these sizes, and you may have to pay extra for specials. One way around this is to design the house with a specific manufacturer in mind, or choose one who doesn’t work to standard sizes.

Opening mechanisms are another thing to consider: most Continental windows open inwards but they rarely suit the typical British house with curtains, instead working better with contemporary designs.

Triple Glazing

ABOVE: JELD-WEN’s DreamVu triple-glazed timber windows promise U-values as low as 0.7. They are clad in aluminium externally (jeld-wen.co.uk).

Double glazing has been required on new homes for nearly 20 years, but a small though increasing number of self-builders are now opting for triple glazing. It’s more expensive and uses thicker joinery sections (which doesn’t suit every location) but it can be more comfortable to live with as it reduces the cold spots around windows. It tends to be a feature of energy-saving designs (though in truth the amount of energy saved in our climate is minimal) and it may well become mandatory in 2013 when the Building Regulations are updated. This DreamVu window from JELD-WEN promises Uvalues as low as 0.7.

Further reading:

• Does Triple Glazing Make Sense?
• PVCu Windows: A Green Option?
• A Guide to Windows and Doors