draughts from underfloor air brick


Postby jls222 » Sat Oct 09, 2010 12:22 pm

My 1945 built house is at bottom of a hill. Cold winds blow down hill through underfloor airbrick under my sitting room floor (under the bay window), so cold draughts come up thru holes around central heating pipes, gas pipes etc. I would like to fit a cowl over the face of the external air brick as this would seem to be the quickest and easiest method of reducing the cold air flow, whilst still retaining some air flow under the floor. Does this sound lke a sensible idea :?: Where would I purchase one from as internet searches have not found a builders merchants selling anything like this :?: Also , any suggestions ref filling gaps around pipes etc :?:
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Postby Perry525 » Sun Oct 10, 2010 7:00 pm

When your home was designed and built, the vogue was lots of ventilation, to help keep the home dry.
With open fires and lots of cracks and holes, homes were cold and drafty.
After the first oil crises things began to change and since then we have had a move away from uncontrolled ventilation.
The move now is that all new homes from 2016 will be air tight to save on heating costs.

If you use your central heating to keep the down stairs rooms warm throughout the cold weather you can block the air vent as the heat from the rooms will keep the joists and floor boards warm and that will avoid condensation.

The space under the floor is usually about 12C at this level the joists have to drop below freezing before condensation will form, the only way they will do this is with freezing air being pulled into the space, by warm air rising inside your home, blocking those vents and sealing the holes has a point.

If you do not keep those rooms warm, then blocking the air vents. (There should be air vents on both sides of your home) To prevent the wind sucking the air from under your home, and replacing it with warm wet air then, there is a very good chance of condensation, damp wood, rot and mould.

The best thing to do is, take up the floor and fix sheets of polystyrene beneath the joists, to keep the joists and floor boards warm and dry.
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Joined: Fri Jul 06, 2007 7:35 pm


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