The area or part of the country you live in will determine how much insulation is required to keep your home comfortable. Older, existing homes, usually require more because the amount installed in some older homes would not meet today's standards.
Air leakage is one of the leading causes of energy waste in most homes and structures. Providing additional insulation where needed makes floors, walls, and ceilings cooler in the summer and warmer in the winter. You can also buy insulation products for residential insulation.
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If you are unhappy paying the never-ending rise in energy cost, then this could be one course of action that could save you hundreds of dollars over a period of a year or two.
The second major benefit could be the dollar savings if you were to do the work yourself. Don't disregard the immediate comfort benefit of feeling warmer in the winter and cooler in the summer because much of the draft has been eliminated.
Consider doing the work yourself if you are up for the challenge. Go to your local building department and request information regarding the present insulation code and guidelines.
Doing the work yourself may not be your first choice. If that is the case, you can look through the yellow pages and find three good qualified licensed contractors to quote your project for you.