Insulation and venting

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In central Texas, where I live, tend to agree on that, especially the attic area. You don't want the attic sealed up as it won't vent the heat, very important especially in the summer. Found the ridge vent system with an adequate number of soffit vents works better than the typical gable vents. Even when using fan aids in the attic with gable vents.
I am confused about the metal roof question though. I thought the insulation for that type of roof was placed between the rafters and the material the metal roof is attached to. Something like Thinsulate for instance.
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Dave

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The issue is "interstitial condensation". Washing, bathing and simply breathing creates water vapour in the house. It's important that this does not find it's way through the structure and condense out on cold wooden roof members encouraging rot. In the UK the normal proceedure is to install a vapour barrier (a plastic sheet) on the warm side of the insulation AND ventilate the cold side of the insulation. If you put the insulation at ceiling level then the whole attic is cold and ventilated. If you put the insuation between the roof timbers then you must leave a 50mm/2" ventilated gap between the insulation and the underside of the roof membrane/tiles. The alternative is to use a vapour permeable membrane under the roof tiles to allow vapour to escape.
An alternative to a ventilated roof is to build whats called a "warm roof" (at least in the UK it's called that). This puts all the insulation totaly above the wooden parts of the roof structure rather than between them. This means there is no cold wood for the vapour to condense onto.
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