Vapor Barrier for Closed Cell Spray Foam Insulation

We’re just about ready to have closed cell spray foam installed (our choice for basement wall insulation). We’ve lined up a great contractor in the Baltimore area who’s going to let us follow him around the basement with our video gear so we can share the whole experience with you. Stay tuned for that in the next 2-3 weeks, we’re sure you’ll enjoy the series.

Here’s two pictures of the basement’s concrete block walls today:

If you’re familiar with most basement insulation methods, you’ll recognize the complete lack of a vapor barrier between the stud walls and the concrete block wall (waterproofed in the white area with Super Thoroseal, and in the grey area with SunnyDry). In most installations, you’d see polystyrene foam board (a.k.a blue board) or a polyethylene plastic, but not here. The reason?

Closed Cell Foam Is Its Own Vapor Barrier

Closed cell foam hardens and becomes it’s own vapor barrier. Each small bubble in closed cell foam is jammed up very close to the bubble next to it, and each bubble is completely closed (creating an incredibly high R value of 6-7 per inch).

1-3 inches of closed cell spray foam is appropriate to create a vapor barrier between .1 perms and 1 perm (the ideal for most areas in the continental U.S.) This provides for inward drying when the sun hits the basement walls in the Summer (and the vapor pressure force is inward), but keeps moist interior air from touching the walls in the Winter (when the vapor pressure force is outward).

Better Than Fiberglass

While closed cell foam costs more than traditional fiberglass insulation, it provides an 80-100% increase in R-value, serves as its own vapor barrier, doesn’t have performance issues even when wet, and is highly resistant to mold growth – all traits that make the cost worth considering, and led us to our decision.

A Note on Open Cell Foam

One quick note to folks considering open cell foam: this product is completely different than its closed cell counterpart. Open cell foam does not act as a vapor barrier, and does experience performance degradation when wet. Given installation cost considerations, we believe open cell foam simply doesn’t make sense for most installations.

What do you think? Will you install closed cell foam on your next insulation project?