If you are going to the expense of insulating the walls or roof of your pole barn with spray-applied foam, you should also address the crawlspace.
- Not doing so would be the equivalent of wearing a snowsuit and winter cap but going shoeless.
- If your feet aren't comfortable, you're not going to be comfortable.
If the floor is properly covered with plastic sheeting, it would be most prudent to insulate the crawlspace walls with closed-cell, spray-applied foam.
This space then becomes conditioned, so you will also want to make sure that conditioned air is circulated throughout the crawlspace to keep this space conditioned and reduce potential for moisture and mold buildup.
Caution on insulating the underside of the roof
You didn't ask, but I want to caution you about insulating the underside of the roof.
- It is my opinion that you should never spray the foam directly against the metal roofing.
- Open-cell foam allows moisture to come into contact with the metal roof, resulting in condensation, and closed-cell foam can hold roof leaks between the roofing, roof framing and the foam until it causes structural damage to the roof and/or its structure.
You should always leave an air gap between the insulation and the underside of the metal roof to allow it to breathe.
- If moisture passes through the insulation, it can be vented to the atmosphere.
- If the roof leaks, it can be removed and repaired without replacing the insulation.
Best wishes on your project.