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Home | Spray Foam 411 | Flood Damage-Resistance and Spray Foam Insulation

Flood Damage-Resistance and Spray Foam Insulation

Closed-cell spray polyurethane foam is the only Class 5 flood damage-resistant insulation, as rated by FEMA

With the rash of rainfall across the Southeastern U.S. in the beginning of October, flooding has again reared its ugly head as a cause of concern for homeowners across the country. Flooding is often a concern in coastal areas, but as we saw with the inland areas of South Carolina, extreme flooding is a serious issue for virtually everyone.


Flooding is the most common and widespread natural disaster in the U.S., causing $3.5 Billion in claims per year, according to FEMA. Naturally, coastal communities should be aware and prepared for these disasters, but the fact of the matter is one in five flood insurance claims originate from areas located outside of high-risk flood zones. In coastal regions, storm surge from hurricanes is a primary threat, but in other areas, flooding can result from underperforming drainage systems or levees unable to withstand over-capacity rivers or lakes.

Obviously, the main cause of damage with flooding is the fact that everything gets wet, which can result in physical deterioration and the perpetuation of mold growth. That being said, hidden contaminants in the water can also result in additional damage. Floodwater often may contain corrosive dissolved salts (in the case of storm surge), raw sewage (in the case of drainage failure), and/or any number of contaminants (e.g. fuel, solvents, chemicals, and/or microbes). As floodwaters rise, water pressure drives these contaminants into buildings, where they seep into porous building materials and require extensive, costly remediation efforts.


Unfortunately, floods are neither completely predictable nor preventable, but with proper preparation, flood damage can be mitigated. Of course, it’s prudent to opt for flood insurance, which at an average annual premium of $700 is a no-brainer when compared to the average flood insurance claim of $42,000. Beyond insurance, homeowners can (and in some cases must) take proactive measures to ensure what is in most cases their most valuable financial asset, their home, is protected from potential flood damage. In fact, the National Flood Insurance Program (NFIP) requires homes at or below the base flood elevation in a given region to be constructed of flood damage-resistant building materials, though this is also a good idea for any home.


FEMA defines a flood damage-resistant material as any building product capable of withstanding direct and prolonged (72 hours or longer) contact with floodwaters without sustaining significant damage. In this case, significant damage suggests a product requires more than just cosmetic repair (e.g. cleaning or resurfacing). Additionally, an important caveat is that flood damage-resistant materials should not cause adjacent materials to degrade.

The FEMA flood damage-resistance classification system delineates five classes in determining whether a material is acceptable (Classes 4 and 5) or unacceptable (Classes 1-3) for use below the base flood elevation. Basically, acceptable materials can successfully survive (after cleaning) the wetting and drying associated with flooding, while unacceptable materials cannot, and so shouldn’t be used in spaces that may be subject to floodwater exposure. FEMA gives closed-cell spray foam the highest rating, Class 5, as a highly flood damage-resistant building product for use as a finish material in floors, walls, and ceilings.



Unlike closed-cell SPF, open-cell foam is rated as a Class 2 finish material. Similarly, cellulose insulation is given a Class 2 rating, while fiberglass insulation is also unacceptable as a Class 3 material.

Why the difference in the rating between closed-cell SPF and open-cell SPF? The simple answer is cell structure. The ruptured cells of the softer open-cell foam readily soak up water, like a sponge, whereas the fully formed cells of the more rigid closed-cell foam don’t permit the penetration of liquid water. Because open-cell foam readily takes up and holds water, it doesn’t dry quickly, which can lead to the deterioration of adjacent building materials. With that in mind, FEMA recommends its usage only in dry spaces that are occasionally subject to water vapor and minimal seepage.

For homeowners looking to improve the durability of their homes, closed-cell foam can offer unique and robust flood damage resistance when applied to basements, crawlspaces, or the underside of the first floor of elevated homes.  •

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