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Check the facts on uPVC frames; Peter Fall explains what to look for when choosing double glazing.

Byline: Peter Fall

WE all have to field these questions - the ones where friends ask for advice on a subject that your job means you should know something about. For me, the questions are always about houses. It may be their own or their elderly mother's or a friend's house - but it rarely requires a simple answer.

It happened the other day: "My sister is looking to replace her windows. Which is the best plastic window manufacturer?" To say that one is the best would require an in-depth study and by the time you have finished the research another half dozen manufacturers will have joined the market and a similar number left. The best we can do is say what you should look for.

Plastic is not strong enough to support an opening window. It has to be reinforced with steel or aluminium sections built into the plastic sections. Once it's in you can't get at the metal so it must be protected against corrosion. Make sure the manufacturer can prove the frames are reinforced and the metal protected. If not, in time, you will find the opening windows sagging or hinge fixings pulling away. For big opening windows, the reinforcement needs to be substantial.

Around the opening there should be a draught extruder strip. Some strips can be a bit feeble so within a couple of years they start to squash down or break up. Check the sample frame and see if you think it will withstand being squashed and freed on a regular basis. Ask how any trapped water might be dealt with. Are there drainage channels built into the frame or will water simply sit in the surround? Your windows should have "trickle vents" which can be left open to provide a small amount of air into the room. These won't prevent condensation in bathrooms and kitchens but will allow in fresh air when the extractor fan pulls the unhealthy moist air out.

A frequent problem is that the external sill is short.

As a result, installers set the frame at the outer edge of the window opening. Windows should be 75mm (3in) back from the front edge of a window opening so they bridge the damp proof course in the cavity walls. Older, solid walls usually have a recess, 110mm (4.5in) back from the face, behind which old wooden sash windows would be fitted. Ideally, the uPVC window should be set into the same recess. To set the windows in the right position, the external sill needs to be at least 100mm (4in) wide so any water runs away from the wall below.

There is a debate over whether the units should be fitted from inside or outside. A unit fitted from inside is difficult for burglars to remove. The disadvantage is that, should water get in between the glass and the frame, it can only leak out into the room. If the unit is fitted from the outside, the manufacturer must incorporate extra security to prevent the window being removed, but any water leak will drain outwards.

One reason water leaks between the glass and the frame is that the glazier stretches the neoprene gaskets when they fit them. When the gaskets shrink back they can leave gaps which let water in.

With these points, and more, you could ask why there isn't a British Standard. There is - or I should say there are - as there are a number of applicable standards. They are produced in a way that doesn't restrict the manufacturers and are mostly to do with testing of the materials. There is a body known as the British Board of Agreement and, if the window has been tested by them, it should give some reassurance. Look for the BBA logo on brochures. It certifies them, but only that they are what they say they are, rather than saying they won't give problems.

Peter Fall is managing director of Clear Building Survey, Call 0800 072 9003 or see
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Title Annotation:Features
Publication:The Journal (Newcastle, England)
Date:Feb 13, 2010
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