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Vapor Barrier Placement with In-Floor Heat – Best Practice vs Plumber Preference? – GreenBuildingAdvisor
8” clear stone > EPS foam > 10 mil poly vapor barrier > concrete slab, with radiant in-floor heat tubing floated in the concrete.
Our plumber won’t float tubing anymore, citing failures he’s seen. He now only installs tubing stapled to foam (like Heat-Sheet or regular EPS) directly under the slab, and places the vapor barrier under the foam instead.
He says Heat-Sheet acts as its own vapor barrier, but we’re concerned this reverses the typical best-practice order — putting the poly below the insulation, rather than directly under the slab.
We’re already into the build and can’t switch trades. Our options seem to be:
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Go with plumber’s method – vapor barrier under the foam, tubing stapled to Heat-Sheet or EPS.
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Stick with our original layering – vapor barrier above the foam, skip radiant heat, and rely on mini-split HVAC instead.
Does anyone have experience with this situation? Is placing the vapor barrier below the foam a long-term risk? Even if Heat-Sheet is truly sufficient as a vapor barrier, we still will be using 10 mil poly under because we are having this come up and over the stem walls as part of the capillary break. So no poly is not an option.
Appreciate any insight or real-world experience.