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I’ve noticed that on new construction in my area (midwest) that I never see both house wrap and insulated sheeting on the outside of a house used together. It’s always one or the other. I’m going to be vinyl siding my house this fall and I’m curious about if I can use both of them together. Is this a safe practice or overkill?
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Jeff,
If you're using extruded polystyrene on the outside of your wall it will act as a vapor barrier; the joints need to be taped with contractor's tape (3M product) and gaps should be caulk or foam filled. Once this is done it will do much of what house wraps do for infiltration from the outside. However, is will not breathe and allow vapor to escape from the inside; instead it will be trapped at the inside face of the foam. Here, where it gets colder than a witches' tit, that's not a desireable thing. It tends to cause some condensation problems in the winter.
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ChadS. Doesn't the rigid foam board insulation (RFBI) raise the cavity temperature? And because of the temperature increase moisture no longer sees cold OSB or plywood sheathing, but the warmer surface of the RFBI? Therefore, the RFBI limits potential condensation.GeneL.
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Gene, would you use a breathable tape to seal the seams of the foam board. I have seen a product that is like tyvek only it is a tape. Or is this not needed. I was thinking of putting foam over cdx sheathing.
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I've noticed that on new construction in my area (midwest) that I never see both house wrap and insulated sheeting on the outside of a house used together. It's always one or the other. I'm going to be vinyl siding my house this fall and I'm curious about if I can use both of them together. Is this a safe practice or overkill?
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Earl. There are those who argue that taping the seams makes no allowance for sloppy construction that would allow moisture to penetrate the wall cavity. Given the interior VDR moisture has no escape route. The point of the RFBI is that should moisture penetrate the cavity its potential for condensation is lessened by the warm surface of the RFBI.
But others, while agreeing with the concept, argue that 1-inch of RFBI is inadequate.
Prudence dictates that one use only dry building materials,and keep the relative humidity at 35% during the heatinbg season.given these cautions then one chooses non-breathing tape.GeneL.