Two different materials for two different jobs. Here is how we decide which one goes where in a Central Iowa building.
Tell us what the Des Moines property is doing and we'll take a look.
Both are two-component polyurethane foams sprayed as a liquid that expands and cures in place. The difference is in the cell structure. Closed-cell foam cures into tiny sealed cells filled with blowing agent; it is dense (roughly two pounds per cubic foot), rigid, and insulates at roughly R-6 to R-7 per inch depending on the product. At about two inches it functions as a vapor retarder and it adds racking strength to the framing it is sprayed on.
Open-cell foam cures with cells that are broken open, so it is soft, light (roughly half a pound per cubic foot) and vapor-permeable. It insulates at roughly R-3.5 to R-4 per inch. It expands far more than closed-cell during application, which lets it fill irregular cavities completely, and it absorbs sound well. Per inch it is less expensive; per unit of R-value the gap is narrower because you need more of it.
Both air seal. That is the point of foam over batts. The choice between them comes down to moisture, space and structure.
Anywhere that touches concrete, soil or steel. Basement walls, crawl space walls, the rim joist and sill, the underside of a metal roof, steel wall panels on a pole barn. In those spots you want the vapor retarder, the moisture tolerance and the high R per inch, because the cavity is shallow or nonexistent and moisture is present at least seasonally.
Closed-cell also wins where depth is limited: a 2x4 wall you want to bring toward the code's R-20 benchmark, a shallow rafter bay in a cathedral ceiling, the underside of a low-slope roof. And it is the choice when the foam is doing structural or wind-uplift duty on a roof deck.
The trade-off is cost and expansion. Closed-cell does not expand much, so it must be sprayed in controlled lifts and the installer has to be careful around wiring and irregular framing. It also should not be the only insulation on both sides of a wall assembly; a wall needs to be able to dry in at least one direction.
Interior partitions for sound. Wall cavities in a new house or addition where the exterior sheathing and housewrap already handle bulk water and the wall is designed to dry to the inside. Some attic rooflines in an unvented design where the manufacturer and the code path allow open-cell with a vapor retarder on the interior in climate zone 5.
Open-cell is not a fit for below grade, rim joists in a damp basement, or steel buildings, because it can absorb moisture and it is vapor-open. In a Des Moines winter, with an average January low of 13.8 F at the airport, vapor moving from the warm side into a cold assembly is exactly what you are trying to control, and open-cell alone does not do it.
We look at what the foam will be sprayed against (wood, concrete, steel, existing insulation), how deep the cavity is, whether the assembly is above or below grade, which side it can dry to, and what R-value the space needs to reach. Then we write the scope with a specific product type and thickness for each area. A typical Des Moines retrofit scope uses closed-cell at the rim, crawl and basement walls, and either loose fill or a foam-plus-loose-fill approach in the attic.
If a contractor proposes a single foam type for every part of your house without explaining why, ask. The answer should reference moisture and drying, not just price.
Questions
It has a higher R-value per inch, which matters when depth is limited. In a deep cavity you can reach the same total R with open-cell or loose fill for less money. Better depends on the location, not the number on the drum.
It can take on moisture and it lets vapor pass, which is why it is kept out of below-grade and high-moisture locations. In a properly designed above-grade wall that dries to the inside, that vapor-open behavior is acceptable.
Properly applied closed-cell adheres tightly and stays put. Problems come from spraying too thick a lift at once, spraying onto a wet or very cold substrate, or off-ratio mixing. Our crews spray in controlled lifts and check substrate conditions before starting.
Closed-cell, on the underside of the steel roof and on the wall panels. It bonds to the steel, stops condensation and handles the temperature swings of an unconditioned or partly conditioned building. Open-cell against steel is a moisture problem waiting to happen.
Tell us what the house is doing and we will come look at where the heat is going.
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