How Important Is Basement Insulation?

Most homeowners don't think of their basement insulation as a prime source of heat loss, yet basements can account for 20 to 35 percent of a home's total heat loss. Basements lose so much heat because of large, uninsulated surfaces above and below grade level. Contrary to popular opinion, earth is a poor source of basement insulation. There is also a lot of air leakage through basement windows and penetrations, through cracks, and at the top of the foundation wall (sill area).

Few basements have any insulation at all, and for most homeowners this means there is great potential for improvement. Basement insulation can often be tied in with other repair or renovation work, such as damp-proofing or finishing the basement.  Generally a basement contractor has two options:  insulating inside or outside.  There are advantages and disadvantages to both.
Insulating on the outside is usually best from a technical point of view. Despite this, it is often necessary to insulate from the inside for economical and practical reasons. Sometimes a combination of approaches is required.
Advantages of insulating inside include the fact that work can be done at any time of year, and the landscaping/driveway will not be disturbed.  However, if the basement has a moisture problem – as many basements do – insulating on the inside is not at all recommended.  Another disadvantage to applying basement insulation on the inside is the difficulty working around obstructions such as electrical panels, wiring, plumbing or stairs. 
Correspondingly, basement insulation on the outside of the house has the following advantages:  the outside wall tends to be more continuous and easier to insulate once the soil is removed, and no disruption in the house or inside space lost.  Disadvantages:  dirt excavation is a complicated and sometimes difficult process. 

Whatever option chosen, it is naturally expected that the contractor examine the advantages of each approach carefully.  Basement insulation is an extremely valuable venture, and is a great way to start off a total finishing project. 

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