Foam Board Insulation: Polystyrene vs Injection Foam

There are a lot of ways to insulate your home including foam board insulation. Foam can be used in various types and forms for insulating walls and roofs. Foam board insulation and injection foam are two more common types used in residential applications. Both types can be installed by the home owner.

Polystyrene Foam Boards

Polystyrene is made up of beads that are expanded and pressed together.  It is similar to the Styrofoam you might see in everyday applications such as restaurant take-out containers. The boards are available in different densities for different applications. Density is determined by the type of the beads used for the board. In manufacturing, tiny beads with liquid pentane are blown into a container to make the beads expand, then injected into the board mould.

High density boards are used for roofing and floor applications as they must be able to bear a lot of weight. Lower density boards are used for walls. Both can be applied on nearly any substrate including vinyl, wood, metal, and brick.  Many distributors will cut the boards to the size needed for the application and come with your choice of coating. Coatings available are non-coated, foil and laminate.

Installation of polystyrene foam boards is simple. An adhesive is used to glue the boards to the substrate. Different substrates will require different types of adhesives. The boards must be covered by drywall or another type of material because of flammability.

Foam Injection

A liquid form of foam can be applied as insulation using a spray gun.  The spray guns have 2 chambers, one for each chemical. When the spray gun is used, the chemicals combine to make the foam. The foam is available in different forms. Small liquid containers are used for repairs, single walls and other small applications. Larger containers, called foamed-in-place use a pressure sprayer for larger applications such as entire basements or new construction.

Foam injection is installed in existing construction by drilling a small hole in the area to be filled then spraying the foam into the hole. The foam will expand and fill the entire area. Entire walls and rooms can be insulated using foam spray by drilling several small holes and spraying. There is some disagreement within the industry whether or not open injection foam is fire resistant but it does have the highest R-rating of retro-fitted insulation available.

 Which One to Choose?

Both foam board and injection foam have the properties necessary for insulation of your home. Deciding which one to use depends on the area you intend to install it. Foam boards can break and chip and absorb moisture. These boards also degrade in sunlight and cannot be easily retro-fitted in existing walls. These boards are best for new construction or unfinished rooms where drywall has not yet been installed. If walls are already installed, they will have to be torn down to use foam boards. Another area boards should not be used is in a leaky basement where there is a chance water might leak into the walls.

Foam injection insulation can be difficult to install for a non-professional. The foam can be used to fill existing walls and do repairs, though it is unattractive. If too much foam is sprayed, it will expand out of the repair or wall area and must be trimmed. Installing foam insulation on new construction or an unfinished room might be ideal for the non-professional since drywall will be placed over the foam and you can make sure the entire area is filled properly. Foam injection is more water resistant than foam boards and is a good option for basement insulation jobs where water may leak into the wall.