Heat is energy. Conservation is needed to keep energy inside (heating season) or outside (cooling season). In the 1970's, the rumor spread that the earth would soon run out of energy. Numerous laws were enacted to conserve energy and invest in renewable resources, including wind, wood, and solar energy. Lower speed limits reduced fuel consumption. The fuel shortage has disappeared, Detroit is producing gas-guzzlers again, the speed limits are back up, and there are no longer incentives for alternate fuels. The only hangover from the energy conservation effort is the insulated floor over a basement that is not vented to the outside.
Anyone who has ever handled fiberglass insulation knows that it is not compatible with the human body. In 1994 the Federal government labeled fiberglass as a possible carcinogen, but lobbying convinced congress that people would not normally come into contact with it in everyday life. In most houses it is buried behind the sheetrock in the walls or above it in the attic. The basement is different. Many people use their basements regularly. Children play there, washers and dryers are sometimes located in the basement. Fiberglass in the floor joists rains dust down as people walk on the floor above, creating a layer of fiberglass dust on the floor waiting to be stirred up when someone walks through it. Any carpenter or technician who has to work in the insulation years after it was installed can tell tales of the mice residing in it, and the unhealthy residue they leave behind.
Does it insulate the first floor from the cellar? Yes, but the temperature difference is probably only 10 or 15 degrees. Is it worth the health risk? Probably not. A quick trip to the attic will show why. The ductwork in the attic is wrapped with R-8 insulation. If there is an air handler up there, it has even less insulation in it. The heating and cooling system is insulated with R-8 or less, over a ceiling insulated to R-38. The 68 degree air inside the house is insulated at R-38, while the 100 degree air inside the duct is insulated with R-8. An extra 25% was added to the system to compensate for loss into the attic.
Why not take the insulation out of the floor joists in the basement and put it over the ductwork in the attic? It would increase the efficiency of the attic system, eliminate the health risk in the basement, and not break any code rules by keeping the house at the AVERAGE energy conservation number as required. It is permissible, as per section 502.2.2 of the International Energy Conservation Code, to over insulate some areas and under-insulate others, so long as the building does not lose more energy because of this action. In this case, the savings could be as much as 20%, if the system does both heating and cooling.
It would also make more sense to insulate the walls of the basement. This would keep the heating system and the plumbing system in conditioned space.
If you are building a new house, take a copy of this to your building inspector and get his permission to make this alteration. Also, never insulate the floor over a crawl space. Insulate the walls of the foundation. It will keep the space drier and eliminate the housing for rodents.