Next-gen sprayfoam systems: shifting to HFO blowing agents

Sprayfoam roofing is ideal for use when: the roof deck is an unusual shape; the region experiences extreme storms, wind, or hail (coastal and hurricane prone regions are two examples); a sloped application is needed for drainage; the substrate has multiple penetrations (such as with solar panel supports) or there is equipment mounted to the roof requiring flashing; the structure is unable to withstand additional weight on the roof; and when removing the existing roof is deemed too expensive (as sprayfoam roofing may be applied over an existing roof in a cost-effective retrofit application).

Installed on the roof, sprayfoam creates a protective, monolithic layer which serves as continuous thermal insulation layer, WRB, air barrier, and vapor retarder. The material requires an additional coating overtop to protect the surface from ultraviolet (UV) radiation, foot traffic, and any other weather cycling and elements. Acrylic- and silicone-based coatings are two which are more commonly used.

Applied to the underside of a roof, closed cell sprayfoam can increase wind uplift resistance. Applied to built-up roofing and metal substrates, wind uplift resistance is enhanced further. A study conducted by the University of Florida in 2007 found that applying closed cell sprayfoam under a roof deck provides up to three times the resistance to wind uplift for wood roof sheathing panels when compared to a conventionally fastened roof.

SPF roofing is also resistant to progressive peeling failure, which leads to flashings and copings being pulled away from their original locations by wind. Following Hurricane Katrina, the National institute of Standards and Technology (NIST) examined roofs and found buildings with sprayfoam roofs performed well without blow-off of the SPF or damage to flashings.

Since it is closed cell, sprayfoam roofing, like closed cell sprayfoam insulation, is also a Class 5 FEMA flood damage-resistant material. It is impermeable to moisture and may be cleaned and dried.

Manufacturing and performance considerations

When developing sprayfoam systems, manufacturers must be mindful of the inherent established precedents in the market. For instance, the plethora of impingement mix 1:1 ratio in the industry today forces manufacturers of new closed and open cell sprayfoam systems to match this chemical blend. The same may be said for when designing sprayfoam solutions with the next generation of blowing agent.

Compared to HFC, HFO molecules tend to break down faster in resin. Consequently, new catalysts were necessary to pair with the HFO blowing agent to sustain the six-month shelf-life industry expectation. This was one of the most difficult hurdles for sprayfoam manufacturers.

The HFO molecule does have a strong benefit over HFC. Thermal conductivity is lower in HFO than HFC. This translates to better thermal performance, on average, with an HFO-based sprayfoam compared to one that is HFC-based. While the blowing agent is the primary driver of the R-value of a sprayfoam, the overall composition of the resin, in combination with isocyanate, determines the sprayfoam’s R-value. There has been an increase in aged R-values in systems containing HFO blowing agents.

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