Question

Do I need to insulate the floor of a workshop?

Asked by Elizabeth
Chester, NY

We have a 30' x 40' pole barn (wood with metal roof) that we are interested in spray foaming. The ceilings are cathedral and the space is open, no interior walls. The existing floor consists of dirt covered with plastic sheeting and plywood built about two feet up from poured cement bases (plywood, 2 feet of air, plastic sheet, dirt). We're looking into two options: 1. Spray foam around the perimeter of the space down to the ground, or as far down as they can get it. 2. Build a frame on the existing floor out of 2x4's, spray foam, then put a second floor on top of the frame. Option 2 is a lot more expensive. Do we really need it? How much difference will it make in insulating the space?

Answer

Elizabeth,

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.

Conditioned crawlspace

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.

Tagged In: insulation, spray foam

Do you have a question about greening your home? GreenHomeGuide invites you to Ask A Pro. Let our network of experienced green building professionals – architects, designers, contractors, electricians, energy experts, landscapers, tile & stone specialists, and more – help you find the right solution.