Code Corner with Wisdom & Associates, Inc.

Use and Covering of Foam Plastic Materials

This installment of Code Corner will go over the requirements for the use and covering of foam plastic materials based on the 2006 International Residential Code.

The recent increase in the use of foam plastic material can be traced to a number of factors, including the fact that foam products offer high insulating values, they can be used as concrete forms, and they generally retain their positive characteristics when wetted. However, the use of foam plastics inside the home is highly regulated because of the toxic smoke that can be produced when these products burn.

The 2006 International Residential Code requires that all foam plastics be separated from the interior of the building, attics and crawl spaces. This would include a crawl space with exposed Insulated Concrete Form block since the blocks are made from polystyrene plastics.

Materials approved for separation

Foam such as expanded polystyrene or urethane spray foam must be separated from the interior of the building by a minimum of 1/2″ gypsum board or other approved materials.

Foam plastics must be separated from the interior of attics and crawl spaces by a minimum of 3/8″ gypsum board or other approved materials.

Even though the code references gypsum board as one product to use for the foam separation in the crawl space, this would not be considered best practice in many areas of the country since the crawl spaces can be damp or wet. The damp crawl space combined with the paper face of the gypsum board could present an inviting envirnoment for mold and might cause more problems than it solves.

Some other approved materials for separating the foam plastics from the interior of the building, attic or crawl space are 1/2″ plywood, particle board, mineral wool insulation or sheet metal. The requirement for covering the foam plastics is to reduce the likelihood of ignition. The gypsum board is not meant as fire-proofing, but rather to delay the ignition of the foam by providing a thermal barrier between the plastic and the flame source.
An exception to exposed foam in the crawl space is for the rim joist area. This exception allows foam plastics to be sprayed into the rim joist area of the crawl space if maximum thickness is 3.25″; the density is between 1.5 and 2.0 pcf, and the flame-spread index is 25 or less and the smoke development index is 450 or less.

Evaluation reports may provide flexibility

Evaluation reports provide some flexibility in dealing with product restrictions within the code. Foam plastics are a good example of how the evaluation reports can help. Evaluation reports are a record of testing a specific product when the manufacturer feels the code is too restrictive or does not properly address the product. In the case of foam plastics, some polystyrene foam products are manufactured with different plastic beads. Some of these beads have a lower flame spread and smoke index than others. The manufacturer of any product can pay a testing lab to run testing and evaluations on the product for specific performance under certain conditions. The published results are called evaluation reports. The reports are good for a specific period of time, usually three years.

Evaluation Reports are product-specific evaluations made by the ICC. They contain valuable information about product usage and the inspector may use the evaluation report instead of the code.

Evaluation reports may allow an exception to the code for a specific building product that meets certain conditions. However, evaluation reports may be outdated, and it is the decision of the inspector whether or not to use them. Visit www.iccsafe.org for details.

Which model code is used in your jurisdiction?

This column discusses current model codes. Some jurisdictions use older model codes and/or make amendments that modify specific requirements. Check with your local enforcement authority for more information. This article is based on section R314 of the 2006 International Residential Code. Many changes have been introduced in the 2006 code from the previous code in regard to foam plastic, so inspectors would be wise to carefully read the applicable sections.

What are flame spread and smoke indexes?

The definition of flame spread is the propagation of flame over a surface. In the building codes, materials with a high flame spread are prohibited from being used as interior finishes. The flame spread index of a material is based on the results of ASTM test E 84. The test procedure involves placing materials in a horizontal, rectangular tunnel with two gas burners. Flame is shot onto the material in a controlled manner and the distance the flame travels over ten minutes is used to determine a materials index rating. Most wood products are less than 200. Fire retardants can reduce flame spread to as low as 25. The smoke developed index of a product is a measure of the visual obscurity created when a material burns. The smoke developed index is a numerical value assigned to products based on ASTM test E 84.