Cavity Draughts


Postby Jackl » Sun Apr 12, 2009 10:33 am

Several years ago when I had upvc double glazing installed the bloke doing it mentioned 'cavity draughts' and he had to take steps to make sure that the sides of the new frames were well sealed. My house was built in 1984 with cavity walls so I assume the airbricks are sleeved and should not be a source of draught within the cavity. If this is correct where do the draughts originate? A little over a year ago I had cavity insulation installed which seems to have reduced/eliminated the cavity draughts. My evidence for this is that prior to the insulation and during periods of strong winds we would need to turn up the central heating thermostat as the house seemed to get colder quicker, this is now no longer necessary with the insulation, but I'd still like to know where the draughts were/are coming from?
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Postby Ken.T. » Mon Apr 13, 2009 7:20 am

Welcome the draughts. If your house was built in 1984 it has been built to last only 25 years. Hermetically sealing a house can cause more problems than not. Think of a house as a living entity, it needs to breath if it doesnt it will get "sick building syndrom".
the reason for your draughts could be many
1. No continuous vent through the cavity
2. No cavity closures at head points sill and jambs (it was common to close cavities in the 80's with bricks that suffer movement allowing air infiltration)
3. Pressure differential from inside to outside accumulating in the cavity causing draughts.

I dont think you can eliminate the draughts, just learn to live with them or even better, sell the house (1984+25=2009)
hope this helps
Ken.T.
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Postby htg engineer » Mon Apr 13, 2009 1:52 pm

'Welcome the draughts. If your house was built in 1984 it has been built to last only 25 years.

I dont think you can eliminate the draughts, just learn to live with them or even better, sell the house (1984+25=2009) '

What type of construction are we talking about here ? standard bricks and mortar or pre-fab ? I understand a pre-fab would only be built to last 25 years, but bricks and mortar ??? - my house was built in 1950's.


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Postby plumbbob » Tue Apr 14, 2009 9:28 pm

If we are talking about a conventional 11" cavity wall, the gap between the walls is open under the eaves all the way round the house.

How much draught circulates around the cavity seems to depend on, well, how hard the wind is blowing and from which direction for one thing, how many holes break through the wall for joists and pipes etc as well as ventilation airbricks for suspended downstairs floors.

Falling inside temperatures during windy weather is not just simply down to drafty cavities, but also to the windchill effect on the external walls and windows, and an increase in airflow through the living areas too.
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Postby Jackl » Wed Apr 15, 2009 9:16 am

Thanks to plumbbob for the info; I guess the bit about the cavity being open at the top, under the eaves, is relevant. Unfortunately I'm not sufficiently agile to check this out but it certainly seems plausible; perhaps if I looked I might see some of the insulation (polystyrene beads) blowing around in the loft? The insulation seems to have inmproved matters; I presume that the draughts were cooling the inner wall, which now no longer happens. I'm reluctant to take up Ken.T's suggestion that as the house is now 25 years old I should flog it as it is doomed; even if I could sell in these difficult times I'd only have to buy another which would probably have problems also, the least of which would be, if new, how close it would be built to adjacent houses, they seem to be packing them in these days. I realise that someone will probably come up with all the problems which cavity wall insulation can cause, there is lots of doom and gloom on the subject on 'the web'. I'll just have to hope for the best and hope that I'll have popped off before too many problems occur. To answer htg engineer; the house is built with inner walls of insulation block which I believe are Thermalite, the outer walls are not standard red brick but some form of manufactured variable size block of a similar colour to Cotswold stone which seems quite porous.
Jackl
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