I have an older home with a cement floor crawl space. It is a cold air space and I would like to insulate and heat the area going forward. The cement floor is in good condition and is mostly covered with repurposed underlay and carpet (mostly to make the crawling bearable). The are no signs of moisture on the floor on on the walls neither. Can I seal off the vent to the outside and insulate the walls with rigid foam board without a vapor barrier? Should I also look at insulating the floor and are there other considerations I am missing? Regards, Brian
You can seal off the exterior vent if you are adding a fan that pushes air in and out of the crawlspace (air circulation, mimicking what that outside vent does). However, those vents are passive and require no power, so why not leave it open and seal it off when temperatures drop below 15-20 degrees Fahrenheit?
You would not gain much from insulating the walls with a rigid foam board. Your best bet would be to insulate under your floor with an R-30 or higher fiberglass batt insulation. That will seal your home tight with insulation from the bottom, while still allowing your crawl space to function properly with ventilation.