Polyisocyanurate (thermax) below grade: any moisture issues?
Hi I’ve read conflicting information about polyisocyanurate and just want to clarify. Some sites say polyiso, unlike XPS/EPS, absorbs moisture from concrete. Is this an issue? I’m interested in putting foil-faced polyisocyanurate against a foundation wall, for potentially unfinished basement space.
If the insulation is properly installed and air-sealed against indoor air, are there any moisture concerns for a) polyiso foam contact against wall and b) polyiso foam contact with slab? I’m less concerned about condensation of indoor air, but outside moisture absorption.
Finally, is there a code reference for what meets code (fire) for foam insulation, i.e. thermax vs EPS with wallboard etc?
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