The use of spray foam to insulate attic spaces can be a real money saver for homeowners in both hot and cold climates. Insulated roof decks allow for the attic to be air conditioned and heated, and this leads to reduced energy costs. However, a poor job of applying spray foam insulation can greatly reduce your savings, or, worse, cause damage to your roof. If you are considering the application of spray foam, then you will want to know what mistakes you should avoid during the process. Below are four mistakes that could prove to be costly.

1. Using open cell foam in a cold climate without preparation

Insulating spray foam comes in two formulations—open cell and closed cell—with both terms indicating how the cellular structure of the foam is created. For open cell foam, the process of expanding foam permits outside air to enter into the hardened foam, thus creating a porous material that permits moisture travel Closed cell foam, on the other hand, is created by using internal gases that emerge inside the foam. It is not porous and will resist moisture.

In a cold climate, the porosity of open cell foam permits air to travel upward into and through the cells, thus resulting in condensation on the underside of the roof decking. Such condensation can soften or even rot the roof structure. Closed cell foam is able to resist moisture travel and that prevents moisture accumulation problems.

That means you should use closed cell foam if your home is in a cold climate, which is defined as Zone 5 or lower in the United States as determined by the US Department of Agriculture. Open cell foam can be used in cold climates, but you must install a vapor barrier on the underside of the decking first to prevent moisture transfer.

2. Applying foam unevenly or too thinly to surfaces

As with any insulating material, spray foam must be applied in sufficient depths to perform as designed. The standard for applying open cell foam is to completely fill the space between framing studs; any less than that, and the open cell foam will not effectively restrict heat transfer. For closed cell spray foam, the depth should be no less than 2 inches from the decking to the surface of the foam.

In addition, depth of the foam should be consistent throughout its application. Even small areas where the foam is thinner than its recommended depth will permit heat passage and bypass the insulating "power" of the remainder of the application. It is better to have foam applied thinly, but consistently, across the entire decking than to have deep areas with gaps.

3. Applying foam in areas where it isn't needed

Another mistake that is easy to make is the application of spray foam in an area where it won't do anything to help. That means spraying foam on every interior surface of an attic is likely to be a mistake. For the most part, there is no reason to spray insulating foam on anything other than a surface that is bordered by the outside air. Placing foam on an inside wall that separates the attic into halves will only waste expensive product.

The only caveat to keep in mind is that insulating foam should be applied to areas where outside air can penetrate; depending on your attic, there may be an opening in between drywall panels where heat transfer can occur. That would be appropriate location for spraying foam even though it doesn't directly back up against the exterior of the home.

4. Failing to mix or apply the foam appropriately

You should avoid mixing the foam components improperly or using an incorrect application technique. Foam should be mixed and applied in a manner that is consistent with the manufacturer's instructions. It may not be immediately noticeable if the foam isn't the correct consistency or if you spray it wrongly; however, as the foam dries, it may contract from the studs and leave gaping holes or fall away from the decking altogether.

To avoid these mistakes or for further assistance, consider contacting companies like Dodge Foam & Coatings Inc.