HouseChalk
Rigid foam insulation
Rigid foam insulation is stiff foam boards used to add continuous insulation on the exterior of walls or under slabs.
Why it matters
It can reduce thermal bridging because it covers studs and framing. It also adds some moisture control depending on the type.
Where people get this wrong
There are different types: EPS, XPS, and polyiso. They have different R-values per inch and different moisture behavior. The right choice depends on where it is used.
Real-world example
Foam boards are installed on the outside of wall sheathing before siding. The studs inside the wall are now covered, which reduces cold spots in winter.
Where this hits your build
This affects comfort, energy costs, and indoor air quality. It gets locked behind drywall, so decisions here need to be right before finishing starts.
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