The Home Energy Audit Chronicle

Insulating the Crawlspace: My Wonderful, Do-It-Yourself Experience

I spent the better part of my weekend addressing the energy integrity of the crawl space under my kitchen. The issue here is a cold kitchen floor during the winter, along with some mighty drafts. What ensues is a story of air sealing and insulating. It's a story completely devoid of glamour. Here's the recap.

The deck on the rear of our house has no more than three feet of clearance from the ground. So you pull out the trellis and crawl under the deck... around the corner... and voila! Here's the trap door to the crawl space:


What a charming space! It's 6x20 feet, with head clearance of about 40 inches. The floor is concrete. It's home to countless rhaphidophoridae, better known in these parts as "cave crickets." Aside from the fact that they jump AT you when you swat them, they are harmless and no more than a nuisance. Cave crickets love the voids between masonry foundations and rim joists. Of these, I have many:


The crawl space was insulated sometime before we bought the house (1998). Unfortunately, the previous job was ineffective: batts of R-11 fiberglass were installed (nominally) between the floor joists with its foil backing facing down, or in other words, away from the underside of the floor above. By this time, any batts that had not already fallen were sagging and ABOUT to fall anyway. So task number one was to pull out all the old insulation.

My strategy called for the installation of 2" thick rigid foam board insulation rated at R-12:


But before I could do that, I had to remove superfluous 3/4-inch wood planking that was attached to the underside of the joists, covering about half the area in total. I'm not sure what this "sandwiching" of the 8" floor joists accomplished. The lower layer had been busted through in places over the years to accommodate electrical and plumbing work. It was anything but air tight. I removed most of the under layer-- enough to allow me to slip sheets of the rigid board insulation in place, flush against the underside of the kitchen floor. Doing so was tricky, since since there were pipes and struts to work around.

This is what the space looked like after clearing out the old insulation, and air sealing the gaps along the rim joist and where walls intersected with the underside of the floor:


Some of the voids in the rim joist were huge, ostensibly for the purpose of running electrical wires and pipes of various description. The previous owner (or some contractor?) loosely plugged these voids with fiberglass insulation. This stuff was soot-stained-- evidence of air penetration and the general ineffectiveness of this approach. This old insulation was removed, the voids were planked over, and the seams were air sealed with a bead of expandable foam:


So now the insulation boards are in place, fit snug against the underside of the floor. They are sealed in place with the expandable foam which works wonderfully as glue. It's hard to see the insulation boards in the picture because they have a shiny metallic surface. This is the best I could do:

Nothing about this was pretty, but the last photo here captures several elements:


The rigid insulation boards are foil backed-- a bit difficult to see here, but it's cut to fit between the joists. You can also see batts of R-19 fiberglass wrapped in plastic bags and fit snuggly (not compressed) in perimeter spaces. The plastic bags prevent air filtration through the batts. This also shows a 1/2-inch water line that has been wrapped in self-sealing polymer foam pipe insulation. That latter item is a precaution: we've never had the pipes freeze, probably because the pipes have enjoyed heat that radiates downward from the kitchen. But the new insulation puts an end to all that: the pipes will be at risk this winter in a presumably colder crawl space. The "whipped cream" is just the expandable foam, which may be too generously applied to seams and voids. I have gone through a couple dozen cans of the stuff (counting the attic work) and still haven't mastered the flow. It sure is handy, though.