Taking a stand on floor insulation

Q: Our Mill Valley, Calif., home was built in 1957 and was not insulated. Every time a wall is opened up, we add insulation. Some say it would be a good idea to insulate the floor of our house. There is a crawl space under the house where we could reach the bottom of the floor. As the house is built on a slope, the crawl space varies from 2 to 8 feet tall.

Others say insulating the floor may not be a good idea. In the summer, the house gets hot, and the coolness of the crawl space will help keep the house from getting hotter.

What do you guys think?

A: Without a doubt you should insulate the floor that separates the living areas from the crawl space. And rest assured you're doing absolutely the right thing by insulating the walls as you open them. You don't mention the attic space. We assume you have some insulation there. Check to make sure it is enough.

Insulation is measured in R-value, which is a measurement used to quantify the resistance of a material to the transfer of heat. Some materials, such as most metals, are good heat conductors; others, such as fiberglass, conduct heat poorly.

Interior air is always trying to seek a balance with outside air. Left to its own devices, 70-degree indoor air wants to transform itself into 40-degree exterior winter air. Insulation inhibits that transformation. The same is true for cooler interior air in the summer. Insulation, caulking, thermal windows and other energy-saving strategies seek to maintain the temperature of conditioned interior air within the living space.

The U.S. Department of Energy provides a chart and map of recommended insulation levels for homes in various climate zones. According to this map, your Mill Valley house is in zone 3. Assuming your heating system is natural gas, the recommended insulation level for a crawl space is R-13, walls are R-13 and attic space is R-38. ...CONTINUED

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