In moderate or dry climates without the threat of sustained subfreezing temperatures insulation between floor joists makes sense.
Insulate floor no crawl space.
In those days common building practice was to insulate the floor above the crawl space and to leave the crawl space s wall vents open so any moisture buildup would vent to the outside a.
Cold air that sweeps through a crawl space meanwhile can lead to cold floors inside the home whether or not the space is wet.
Fiberglass insulation batts or rolls are the most economical and easiest diy choice for insulating between the floor joist in a crawl space.
Floor insulation for moderate climes popular reads.
A temperate lower area that will keep upper floors warm while your home s foundation remains in sound condition.
That doesn t mean it s a problem but it isn t needed.
Where winter temperatures are extreme opt for insulating the walls and sealing off the crawl space entirely.
Unless there are excessive moisture problems in the crawl space use unfaced fiberglass batts to insulate the walls.
If as you say the floor is only dirt covered with a vapor barrier then there would be heat loss there.
Department of energy recommends r 11 3 insulation under floors in warm climates and an r 25 6 to 8 in cold climates.
A crawl space under a house helps protect against certain pests but a crawl space with abundant moisture can invite problems including mold wood rot and vermin.
Insulation also helps to preserve the air quality and reduce energy costs.
Determine if you need conditioned air a dehumidifier or both add conditioned air if you have problems with.
Insulation is to keep heat from moving from one place to another so if the crawl space is heated then the insulation is not needed.
Crawl space insulation as a part of overall home air sealing and insulation helps maintain your entire home s energy efficiency without insulation heat and cool air are easily lost through the floor.
Proper crawl space insulation also can prevent your crawl space from becoming a moist environment that grows and harbors mold and mildew controlling crawl space temperature and moisture is a dual process that works toward a common goal.
That s especially true when heating ducts or pipes pass through the space.