Spray foam or zip r for cold floor – GreenBuildingAdvisor

Ryan,

Your assembly with Zip-R on the underside is what is most usually suggested when this comes up here, for raised floors open to below. The only complications are when it is too close to grade. If you can get under there it will work well.

Depending on how worried you are about rodents, you may want to line the underside with hardware cloth, either above or below the Zip.

This section is from GBA