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Old 01-08-2012, 08:41 PM   #31
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I was surprised to see foil-faced polyiso after the 2" of XPS in the wall, acceptable to BSC after all the studies against in below grade. Other articles of theirs use polyiso below grade when leaving it exposed (without drywall) and change it out before drywall.... The dew point is safe because of so much foamboard that the amount of interior diffusion from the basement is a mute point and the concrete will never get basement air to it.

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17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?
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Old 01-08-2012, 11:48 PM   #32
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ok. got it. john
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Old 08-13-2012, 03:34 PM   #33
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There are two sides to this story, one water making its way through the walls and floor, result a damp surface and water vapor made in the home and condensing on a cold wall or floor.
With the outside water making the surface damp, then exposure to warm air will keep this under control.
With water vapor in the air, then you can either keep the wall surface temperature above dew point, or use a water vapor proof plastic sheet backed by polystyrene to keep the water vapor away from the wall.
The water vapor proof plastic sheet, will fail if the insulation behind it is so thin that the surface temperature is below dew point and condensation will form on the plastic. If the plastic sheet, is not perfectly water vapor tight, due to poor installation, and the insulation doesn't keep the suface warm enough then the water vapor will pass through the plastic and condense on the cold wall/floor.
It is very difficault to fit a water vapor proof sheet over a wall or floor and to get it to work as intended, as the water vapor molecules are very small and they can pass through many things always attracted towards a cold area or surface.
Keeping things warm and avoiding condensation by letting convected warm air flow over them is much easier.
Think of a typical window during the winter.....during the day with warm air flowing, the window stays clear. Close the blinds or curtains at night and the space behind losses its warm air circulation, temperature falls and condensation forms.
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