I'm currently doing a full house renovation, taking off all the internal drywall and moving a few walls to reshape the layout with a new kitchen and bathroom. I'd also like to update the insulation while the framing is exposed.
Plan
My intention is to fit rigid foam board between the studs and seal the foam board to the studs (unsure exactly how yet, maybe insulation tape) to create an airtight seal, followed by a layer of plywood fixed to the studs to increase structural strength/ shear strength of the house (as we live in Japan – an earthquake zone), followed by another layer of foam board, followed by drywall.
Question
My concern is about condensation forming inside these layers (or anywhere, really). The climate is hot (often 30°C+/ 86°F+) and humid in the summer, while very cold (0°C ~ -10°C/ 32°F ~ 14°F) and snowy in the winter. Winter seems to last about 4 to 5 months, so I'm really want to get in as much insulation as possible.
Can anyone weigh in on the safety of this strategy??
Also, I intend to leave a small gap between drywall and foam board, but is this necessary?
Best Answer
Where in the world do you live? Most earthquake zones are temperate climates in the US. It sounds like your sealing may create more of a problem as you will end up with a double barrier or even 3 if the house is wrapped trapping moisture. The Pacific Northwest in the US is one of the cooler earthquake zones but also the wettest and this sandwich would setup a great home for mold. The insulation in the walls with an additional layer of plywood would help seal. I think the extra layer of foam is asking for trouble long term.