I will be insulating and dry-walling my detached garage in the near future. The garage currently has unfinished 2x4 walls with plywood siding on the exterior. There is currently not a vapor barrier in the wall at all.
Living in Seattle, we can have a pretty wet climate. Before I close up the walls, do I need to add a vapor barrier? What options of products do I have? Is it worth removing the exterior panels and installing a film between the studs and siding? Is there an insulation that is recommended for this type of application?
Well, a lot depends on whether you are going to heat it at all or just leave it cold.
A differential in temperatures will normally cause moisture to move through walls hence the need for a vapour barrier, or retarder, and an issue you have that other don't is lots of bul water from rain. Of the two issues, rain may be your biggest worry in keeping your garage dry, as opposed to keeping it warm.
If you have the chance to add a house wrap and/or to improve that situation, then your climate would tell you to do that first. Put it this way, a heated garage that leaks from the rain is no good at all.
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