If your crawl space doesn't have insulation or if the insulation it has is wet and falling apart, talk to your insulation company about your options. It's a good idea to have insulation in a crawl space since the air from it wafts up to your living area.
Fiberglass batt insulation was popular at one time, but there are better options now that stay put so you don't have to worry about the insulation falling or getting moldy due to moisture. Here are options for crawl space insulation.
Spray foam can be a more costly option, but it does a good job of insulating a crawl space. The foam adheres to the ceiling and walls and won't fall off. It won't be ruined if it gets wet, and it seals gaps in the ceiling to reduce the number of air leaks.
Spray foam is difficult to work with, and it has to be installed by a professional. The insulation company may recommend encapsulating the crawl space with a vapor barrier first to help keep down moisture. With a vapor barrier on the floor and walls, and spray foam insulation added, your crawl space can stay dry with improved climate control. You might also add a dehumidifier to the encapsulated space to help the area stay even drier so mold won't be an issue.
Another way to insulate a crawl space is with foam boards. These can be attached with adhesives or concrete screws. Your contractor may use both in case the adhesive fails. The insulation company may cover the walls and ceiling with these boards.
A good thing about using rigid foam is that it can be cut easily to any size that's needed. That allows the insulation company to get a tight fit in the ceiling framing to block air leaks. They may also seal around the edges of the boards to help hold the foam in place.
No matter what kind of insulation you have added to your crawl space, the contractor will probably leave a few inches along the wall accessible for a pest control company to check and treat for termites. The foam boards might also be combined with vapor barriers that also help slightly with insulation and dampness control.
In addition to installing insulation, the insulation company also wants to seal up gaps and cracks in the walls and ceiling to control air drafts. This might be done with canned spray foam. Adding insulation to your crawl space could make a difference in your comfort upstairs. Plus, you might notice a decrease in your power bill when your home has added insulation.
You may also want the insulation company to check the insulation between your exterior walls and attic to make sure it is in good shape and able to control the climate in your home.