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In cool or cold climates to do a proper job of making an air tight building you need to put a vapour barrier on the warm side of the insulation.
During winter warm heated, moisture laden air is trying to get to colder drier air and vapour barrier prevents it (a good thing).
In summer the same thing happens but in a air conditions houses the warm moist air is travelling through the wall into the house.
When does it become a problem? Potentially condensation could occur inside the insulation or the outside of vapour barrier!
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In England the only place thatI have ever seen summer condensation is on floors and then only once on a particularly humid hot day which fast followed a cooler snap. Lots of floors were cool enough to catch some condensation. I think even if this were to happen inside walls it would be very rare though with increased use of air cooling this may become a problem that should be adderssed.
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Definately a problem .....in theory. There are some "change of state" materials around that profess to solve the problem. In practice (and I'll get some flack for this I expect) there is not that much temperature and vapour pressure difference across the wall in the summer season to cause a problem.
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I have a wall in my 18th century brick house that regularly got soaked with condensation every summer. Warm wet air met cold wall. Previous owners had used gypsum plaster and then tanked with concrete when some idiot surveyor diagnosed 'ising damp'. The problem was cured when I stripped off all the inappropriate impermeable materials and replastered the wall with lime. I now have an absorbant, breathing wall and no sign of condensation.
Vapour barriers just get in the way of water movement. Don't use them.
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"Vapour barriers just get in the way of water movement. Don't use them."
But Biff, doesn't not using them compromise airtightness as suggested above. And won't it also lead to condensation/damp on the cool side of the insulation? I'm thoroughly confused about this.
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