Taking a stand on floor insulation

Best plan: Match to climate zone

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?