What Is Foam Board Insulation?

Written by emily patterson
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Foam board insulation, also called rigid insulation or beadboard, consists of large sheets of plastic foam. There are a variety of R-values, or measures of thermal resistance, used for different areas that are to be insulated. Foam board is easier to work with than fibreglass insulation because they are in rigid sheets and do not have the associated fibres that can cause allergic reactions such as itching and sinus congestion. In addition, foam board insulation is more resistant to mould and mildew than fibreglass insulation.


Foam board insulation can be used in most areas of a building. It can be installed on the exterior of the building during construction or under siding. This insulation can be used between studs on interior walls as well as over concrete walls to insulate basements. Foam board insulation can also be used to insulate ceilings and roofs. A variety of R-values allows for using the most effective, least-expensive option based on the thermal resistance needs of the area to be insulated.


Foam board is made from either polystyrene, polyurethane or polyisocyanurate. Moulded, expanded polystyrene (MEPS) is commonly called beadboard and can be used for applications such as roofing insulation, depending on the density of the product. Extruded expanded polystyrene is more uniformly dense than MEPS and has a higher resistance to moisture. It is also used for roofs and low walls where moisture can be a problem for other types of insulation. Polyurethane and polyisocyanuarte have higher R-values in a thinner board and are used for applications where there are space limitations for other types, or less expensive, insulating options.


Foam board sheets are available in 4-foot-by-8-foot sheets. It can be cut to size with a utility knife or small handsaw. The thickness of the foam board insulation can range from 1/2 inch to 4 inches, depending on the type of insulation and the R-value. A benefit of foam board is that it can be cut to fit in very small as well as irregularly shaped areas for better overall insulation.


A vapour barrier should be used in conjunction with foam board insulation to reduce air flow and to reduce the decline of the R-value as the material ages. Reflective insulation is often used to protect foam board from reduced R-value due to ageing and reduce condensation that can lead to rot. Adequate ventilation is also needed to reduce the risk of moisture from becoming trapped in the foam board insulation which can cause mould or mildew issues.


With foam board insulation, there is less irritation during installation than fibreglass insulation. Foam board easier to install than fibreglass insulation and can be installed with glue or nails instead of staples, which is a beneficial time-saver, especially when working overhead. In addition, a higher R-value can be achieved in a smaller amount of space. Foam board can also be used on the exterior of a building to provide additional insulation.

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