Moisture Barriers and Sprayed Foam Insulation

Is a moisture barrier required in addition to sprayed foam insulation?

by Jon Willis, CSI-Denver Technical Chairman

If the sprayed foam is of an open-cell type, it is not watertight and a moisture barrier is required as a part of the wall construction. (Note that use of open-celled products outside of the building enclosure is not recommended because these products will absorb moisture and, especially in cold climates, will freeze and decay. Open-cell products will also loose their thermal characteristics when they are saturated with water.)

Closed-cell sprayed foam insulation is generally considered to be moisture tight and is typically touted as such in the manufacturer’s data sheets. For example, Demilec USA claims its HeatLok Soy product has been “formulated to meet the intent of the International Code Council (ICC) building codes and is used primarily as a vapor barrier, air barrier and thermal insulation.” Meeting the intent is not the same thing as having an ICC approval. Bay Systems has an ICC Evaluation Report for its BaySeal CC foam, but that report only evaluates the product as a thermal insulation and as a vapor retarder and not as a moisture barrier. Dow Chemical claims it’s Styrofoam Brand SPF Insulation – RS is a “monolithic barrier for protection against water and air”. However, careful reading of the literature indicates that is only the case when combined with other wall system components. The Dow sprayed foam itself will not qualify as the moisture barrier and has no ICC approvals as such.

The ICC currently recognizes Grade D paper, 15 pound building felt and other approved materials (such as Tyvek HouseWrap, etc.) as moisture barriers. The criteria used by the agencies writing the ICC Evaluation Reports is that the product is equivalent to Grade D paper with a 60-minute water-resistance rating as described in IBC Section 2510.6.

Although the sprayed foam products may have a good chance of obtaining the required ICC approval, as of this writing, this author is unaware of any closed-cell sprayed foam materials with an approved ICC Evaluation Report as a moisture barrier. As such, it is probably best professional practice to include some other form of moisture barrier on the building sheathing, such has No. 15 building paper, below the sprayed foam until such tests and approvals are received. The other option is to see if the local building authority will approve the sprayed foam based on the test reports they have. I consider this as an outside possibility. Even so, in our litigious society, the lack of an ICC-approved moisture barrier may add unnecessary ammunition to a future lawsuit.

There actually are 2 sprayed-foam insulation products, by one manufacturer, that have an ICC-ES Evaluation Report which states that they can be used as water-resistive barriers. The report says that they may be used as the water-resistive barrier prescribed in IBC Section 1404.2 (not Section 2510.6, as mentioned in the above article, but I believe that Section 2510 is just regarding Stucco.) The products are Insulstar and Insulbloc, produced by NCFI Polyurethanes.

The address for the ICC-ES Evaluation Report:

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