Hello!

Quick background: 1200 sq.ft. ranch style home, build ca. 1980, with dirt-floor crawl space, rolled fiber-glass insulation in the gaps between joists, and no HVAC ducts. When purchasing the home (two years ago) moisture problems in the crawl space came up during inspection, but the seller refused to do anything about it, and since we were getting a good deal on the place anyway, we let it slide.

This past summer, we installed a drainage system (drain tile around the perimeter of the crawl space which feeds any groundwater or rain seepage into a sump pump). So, we don't have any standing water under there. However, the crawl space has a dirt floor, and it is vented, so I am sure that we still have moisture problems (rising from the dirt ground) as well as humid outside summer air (we're in Central Kentucky) through the vents.

My Question: is it possible to have the all visible wood surfaces (floor joists and beams) covered with spray foam insulation, as a way to protect them from humid air? Of course, the encapsulation method (basically, sealing off all outside air and covering the floor and walls with thick plastic) is the traditional remedy for this problem, but quotes I've received from local providers are in the range of $6,000--yikes! My thinking is that, if spray foam insulation covers the wood with a barrier that cannot be penetrated by moisture, why would a full-blown encapsulation be necessary?

 

First, spray foam isn't cheap either...

Second, you can't leave foam exposed; it needs to be covered with a thermal barrier because it gives off noxious fumes when exposed to fire.

Third, if there are cables and pipes running through the area, you can't encapsulate them in foam.

So I think there is a reason lining the space with thick plastic is the common solution.

If there's room to move around down there with reasonable comfort, putting the plastic down is a reasonable DIY....Fastening it to the walls takes some care, as does overlapping and taping the joints, but nothing really hairy.

 

I would put a vapor barrier on the floor and see what happens. Your space is set up to be vented to the outside and sealed off from the house air. Should you want to change that, the insulation then goes on the wall and not the ceiling of the space. In either case, there should be a vapor barrier on the ground.