Like the attic, the crawlspace is often an area that is overlooked for regular maintenance. My home is no different. In case you are not sure whether you have a crawlspace or a basement, a crawlspace is characterized as being an accessible but unfinished area beneath your home. There are two types of crawlspaces. There are vented and unvented crawlspaces. If your crawlspace is vented you will see foundation vents in the concrete foundation of your home that are designed to be open in the warmer months and closed in the cooler months. If you don't see these vents, your home has an unvented crawlspace. It is important to determine which type of crawlspace you have before beginning any work because from an insulation standpoint these would be treated differently.
The one commonality in the treatment of vented and unvented crawlspaces is the need for a vapor barrier. Because the crawlspace is an unfinished space, moisture from the ground can accumulate causing mold , odors and other structural issues. The recommended treatment for installing a vapor barrier in the crawlspace is to cover the floor with 6mil plastic sheeting. Working in rows, the pieces of sheeting should overlap each other by approximately 12 inches, should extend up the wall a few inches then be secured with tape. Hold the seams in place with tape, scrap lumber or rocks. Once the vapor barrier is in place you are ready to begin insulating.
The recommended treatment for insulating a vented crawlspace is to fit kraft faced insulation batts into the floor joists. The kraft paper acts as a vapor retarder and should face against the floor deck. The insulation should fit snuggly, leaving no holes or seams where air can pass though and upwards into the living space. Staple the flanges securely to the sides or bottoms of the joists. Because over time the insulation can sag, it is important to use wire fasteners, or chicken wire to hold the insulation in place. Wire hangers should start at least 6 inches from the end of each batt and repeat no more than 24 inches apart. Do not compress the insulation when installing the hangers. Insulation that has been compressed loses its R-factor.
For an unvented crawlspace it is recommended that the walls and the header joists be insulated. The header joists run across the ends of the floor joists. Measure and cut pieces of un-faced fiberglass batts and place them against the header joists . This should be repeated between each floor joist, completely filling the spaces that have been enclosed by the the floor joists, subfloor , and the sills. The key to installing a successful air barrier is a snug fit, with no gaps or holes. Once again, we are not compressing the insulation! Instead of insulating the floors, in the unvented crawlspace, we are insulating the walls. Spray foam insulation is the ideal product for this application because of the ease of installation. If you aren't using a spray foam application the process would be install fiberglass batts to the sill with furring strips. These should be nailed to the sill plate and the insulation should hang down the wall and extend into the crawlspace approximately 24". Anchor the the insulation where it meets the ground with 2X4 s. Anchor as close the wall as possible. As always, when adding insulation, gaps and cracks should be avoided so the batts should be butted up as closely as possible to one another.
Properly maintaining the crawlspace area beneath your home will not only save money on the utility bills but it is also an investment in your health and the longevity of your home.