The foundation of the home is a large slab of material - generally stone or concrete - that is built on top of the Earth where a home is to be built and supports the building from underneath, promoting stability of the structure of the home. The foundation is just one component of the building envelope.
Although a necessary component of the building envelope, the foundation of the home can frequently be overlooked when retrofitting is being done and energy efficiency is being improved. Generally speaking, when insulating a home little thought is put into how the foundation should be insulated. However, insulating the foundation is a critical component of having an energy efficient home. It is estimated that about 15% of heat in homes is lost through basement walls and the foundation footings. Recommendations for foundations include insulating them with material that has an R-value of approximately R-20 to R-30, not as much as walls but still enough to keep the cold out and the heat in.
To ensure that the foundation of a home is still performing at its peak, Natural Resources Canada recommends evaluating the foundation every 20 years and doing the necessary repairs. With the most common type of foundation - concrete slab - improving the foundation is quite simple as insulation can be added from the inside or the outside as long as there is no significant water intrusion into the home and no other significant structural issues exist. In addition to insulating the foundation, drainage should be evaluated and changed if needed to ensure that drains move water away from the outside of the foundation.
When insulating foundations, you have the option to do it internally or externally. Insulating from the inside can increase the risk of freezing if the foundation is close to the frost line. If possible however, the benefits are significant. Note than only sealed, well-drained concrete foundations should be insulated from the inside. To insulate from the inside, the use of a moisture-resistant insulation is recommended, such as polystyrene insulation. Mineral wool and fibreglass are also good options so long as they are paired with a waterproof component. To insulate from the outside, the soil around the outside of the home must be excavated down to the base of the foundation. Then, a rigid polystyrene insulation must be extended over the full height of the foundation, and must stay protected from the sunlight. As well, a waterproof membrane should be used. Note that stone and concrete block foundations must be insulated from the outside.
There are several different ways that a foundation can be made, and the type which should be chosen depends on the area where the home is being made and the soil type it is being built on. A couple of the different types of foundations are: