Foam is a Fire Hazard
Semi-permeable rigid foam insulation and spray foam insulation (foam plastic) on the inside of basement foundation walls is often found during an inspection of the full-basement foundation of a house. Its use could be a good strategy for a moisture-resistant finished basement. However, fire and smoke characteristics of this type of insulation require that it be covered with a fire-resistant layer, such as gypsum wallboard (drywall).
Sometimes this requirement works fine when the basement is being finished. This requirement of having spray foam insulation to be protected by a thermal barrier is found in the International Residential Code (IRC) 2015 Section R316. In most cases where spray polyurethane foam insulation is installed, the foam should be separated from the interior living spaces by an approved thermal barrier of at least 1/2-inch gypsum wallboard (drywall), 23/32-inch wood structural panel, or a material tested to meet the acceptable criteria from NFPA. There are a few exceptions to this requirement, including flame spread index ratings.
If a basement will only be insulated and not finished, a fire-rated foam panel or similar fire-rated covering needs to be used. Because the above-grade portions of the basement wall can dry to the outside, fire-rated insulation on these surfaces may be of an impermeable type. For example, it can have a foil facing. But insulating approaches that restrict the drying potential of below-grade portions of the foundation wall toward the inside should be avoided.
In attics, a thermal barrier is not required when several conditions exist. Those conditions are listed within the IRC Code 2015 Section R316, and they include the attic access is required, the attic space is entered for only maintenance and when repairs are needed, and the foam insulation has been tested or the foam insulation is protected again ignition using a listed barrier material.
Packages and containers of spray foam insulation (or foam plastic) should be labeled and identified if they are delivered to a building site.
Open-Cell Polyurethane Foam
Open-cell polyurethane foam (OCPF) is a soft, flexible, spongy insulation with broken cell walls that permit air to fill them. They typically have a density of 0.5 lb/ft3 (8 kilograms per cubic meter [kg/m3]), which is significantly less than closed-cell insulation, as well as having a reduced R-value per inch, although OCPF still has excellent thermal-insulating and air-barrier properties. The foam is weaker and less rigid than closed-cell foams, too. It will require trimming and disposal of excess material as it expands to over 100 times its initial liquid size.
Builders often choose open-cell foam for the following advantages it affords, including:
its low cost. Where economical yield is important, open-cell foam is generally chosen over its more costly alternative;
providing a sound barrier. OCPF forms a more effective sound barrier in normal-frequency ranges than closed-cell foam. For this reason, OCPF is well-suited for installation beneath floors and around theater rooms;
its flexibility. Open-cell foam is more flexible than closed-cell foam, which allows it to adjust to weather-induced expansion and contraction of framing members. CCPF, by contrast, may develop hairline fractures because it cannot flex sufficiently; and
its permeability to moisture. While often cited as a reason to avoid the use of OCPF, in certain situations, it can be helpful for moisture to pass through insulation. Open-cell foam used in roofs, for instance, will allow a roof leak to make its way to the space below where it is more likely to be discovered. Closed-cell foam used in the same application would trap the moisture, hiding the leak and potentially leading to wood decay. In most situations, however, OCPF should not be used in any place where it might become wet, as moisture will diminish its insulative value. InterNACHI inspectors may call out open-cell insulation discovered in moist areas, such as in external applications or below grade.
In summary, polyurethane foam is available in two varieties that are suited for different applications.
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