Timber is tops in architect’s guide to choosing new windows

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Sam Foster, architect, www.samfosterarchitects.co.uk

Windows and doors. We all have them and at some point there’s a very good chance you’ll buy some. We take them completely for granted, assuming that they’ll let light in, keep the wind and rain out, provide ventilation, give us connection to our surroundings and stop folk from breaking in.

Suddenly that’s quite a few things to ask from a bit of frame and glass, so what should we be looking for? Well, let’s start with the basics:

*Provide security. I’m not sure how many of us lock our doors and windows during the day, but we do when we go away. Locks and security features on windows and doors are quite sophisticated so the simplest thing to do is make sure that they achieve “Secure by Design” status. This is a standard set out by the Police that says that they’re very secure. It can also make a difference to your insurance premiums. It doesn’t involve keypads or retina scanners, just good quality locks and ironmongery and most manufacturers offer this.

*Stop the heat getting out but allow the light and views in. Believe it or not, the glass in windows and doors is much more insulating than the frame, so the bigger the unit (and the higher the proportion of glazing to frame) the

more insulating it’s likely to be. While double glazing is standard these days, triple glazing is becoming more popular though it costs around 20 per cent more. Depending on how much energy this might save, the upgrade may be worth thinking about. Danish firm Rationel produce both double glazed and triple glazed bespoke timber windows with options for an alu-clad outside finish, which increases the life of the windows.

“But don’t windows lose as much heat as they let in?” I hear you ask. The answer lies back in high-school physics…the heat and light from the sun is emitted as long-wave radiation. When this passes through glass it changes to short-wave radiation, which doesn’t readily go back through glass. Once inside a room this short-wave radiation bounces about and is absorbed by what it strikes, like floors, walls and furniture. It’s also absorbed by the frames and glass of the windows and doors and then conducted back outside.

Window frames made of timber act as an insulator. If the windows open they should have at least two sets of gaskets between the frames. Glazing should have argon in the space between the panes of glass as this reduces the amount of heat that will escape out, and the “spacer bars” should be classed as “Warm Edge”.

When all of these features are taken into account we end up with low heat loss, called its ‘U-value’, Building Regulations currently require windows and doors in new buildings to have a u- value of no more than 1.8W/m 2 K and less for extensions. The British Fenestration Rating Council has a useful website that explains the energy efficiency of windows. There’s no point in getting fantastic windows if they’re poorly fitted.

Make sure the gap between the window and the hole in your house is tightly packed with flexible insulation to stop draughts and heat loss.

*Sash and case are usually the draughtiest, purely because of their sliding design. Windows that compress a seal when they close, like any hinged window does, tend to be more draught-proof.

*I prefer timber windows with aluminium external cladding. Timber is the most insulating of all materials and aluminium protects it from dampness.

You only need planning permission to change your windows if you live in a listed building or conservation area.

*Article courtesy of Sam Foster Architects and Rationel windows