Spray foam insulation has become a trusted tool for builders aiming to create tighter, more energy-efficient homes by providing insulation and air barrier in one application. But to get the full value, builders need to plan, choose the right type, and work with trained installers.
Here’s what you need to know.
Choosing the Right Foam: Open-Cell vs. Closed-Cell
The choice between open-cell and closed-cell foam depends largely on climate zone, application, and performance priorities.
Open-cell is typically used in interior applications in warmer climate zones (1–4), such as wall cavities or unvented attic assemblies. Its sound attenuation properties also make it ideal for reducing outdoor noise in urban or high-traffic areas. Also, certain approved open-cell formulas can also be used in the fire-rated partition walls of attached single-family homes.
Closed-cell is preferred in colder climates (zones 5–8) where a Class II vapor barrier is required. Its dense structure provides moisture resistance, vapor control, and structural strength, making it suitable for exterior or below-grade applications like sealed crawlspaces and radon abatement. “You also get an R-value above 16 in a 2×4 wall due to its high R-per-inch,” says David Dietrich, National Residential Manager at Huntsman Building Solutions.
Factors That Guide Strategy
Climate, code, and substrate conditions should guide insulation planning from the outset. “Builders must consider humidity levels, vapor barrier requirements, and even allergens or noise pollution when configuring the envelope,” says Mickel Maalouf, Huntsman’s Sustainable Building Science Manager.
Code compliance is determined by the state-adopted International Energy Conservation Code (IECC), which specifies minimum R-values and blower door testing standards. While builders can follow the prescriptive path (meeting code exactly), many opt for the performance path, which uses third-party testing and trade-offs—a natural fit for spray foam thanks to its dual role as insulation and air barrier.
Prep Makes Perfect
Proper prep is critical. “Spray foam isn’t fiberglass—it can’t be treated the same way,” says Daniel Kinard, Huntsman’s Technical Service Director. Builders must ensure that drop walls, garage walls, and other surfaces have a substrate or backing to support the foam.
Because spray foam is both a building material and an installation method, the installer’s experience matters. Builders should confirm their contractor has manufacturer training and current certification.
Builders should also confirm the installation crew has completed training, either through the manufacturer or the Spray Polyurethane Foam Alliance.
“Check the drum label to ensure you’re getting the product you paid for, and verify they’re applying the proper fire protection coating when required,” Kinard adds.
Radon and Below-Grade Applications
Closed-cell foam’s performance below grade offers unique benefits. In radon mitigation systems, it replaces the need for a taped poly barrier by creating an insulated monolithic vapor and harmful gas barrier under the slab.
“It’s 65 to 100 times more resistant to radon diffusion than 6-mil poly,” says Maalouf. “It also adds thermal insulation and requires less labor and sealing at junctions.”
Performance You Can Sell
When explaining spray foam’s value to homeowners, Dietrich recommends framing it in terms of comfort, health, durability, and efficiency—the pillars of a high-performance home.
- Comfort: Spray foam minimizes hot and cold spots and reduces outdoor noise (open-cell).
- Health: It seals out dust and allergens and blocks harmful soil gases like radon (closed-cell).
- Durability: Spray foam maintains R-value, air sealing, and vapor control for the life of the structure.
- Efficiency: Properly applied spray foam can significantly reduce heating and cooling costs. Because of this, builders should ensure HVAC equipment is sized properly. “Too big a unit leads to short cycling, poor humidity control, and wasted energy in a tightly sealed foam-insulated home,” Kinard says.
Closed-cell foam also improves racking strength, enhances wind uplift resistance, and is rated by FEMA as resistant to flood damage.
“It’s not just insulation,” Dietrich says. “It’s a high-performance system that, done right, improves everything from occupant comfort to the bottom line.”
Learn more about spray foam systems, resources and product options.