What's the best way to insulate a floor over a crawl space?

Question

I have a crawl space that is roughly 50 square feet in space. The previous home owners installed a piece of plastic sheeting on the crawl space dirt floor. The floor above the crawl space is extremely cold during the cooler seasons. I've been researching a lot about insulating the crawl space, but still cannot decide on which of the following:

1. Installing fiberglass batts in the crawl space ceiling and rim joists or
2. encapsulating the crawl space using rigid foam and 6 mil plastic sheeting.

I received quotes from multiple contractors that vary from fiberglass batts, rigid foam, spray foam or a combination of all three. The pricing is varying from $200 to over $2000 in some cases.

Ultimately, I would like to know which option is best. I've included pics of my crawl space.

My basement does have high humidity in the summer months, but I do have a dehumidifier that runs when it hits 55%. I am not sure if this will be a factor.

Any advice is appreciated.

Answer 1

The 'best' option is full encapsulation and insulation. This is the recommended method today. The primary arguments are:

• humidity levels in an encapsulated space are much lower than vented spaces
• due to it being encapsulated, it's much cleaner which can improve indoor air temperature (no pest droppings, dust, mold, pollen, etc. migrating up through the floor)

However, if you don't want to go that route, there are recommendations for insulating just the underside using rigid or spray foam. Building Science Corporation has recommendations.