How to Insulate Your Basement or Crawl Space: Do it Yourself

In many older houses crawl spaces were used in the rooms that were extended beyond the main foundation of the house, added on rooms and entire houses built on a crawl space with an exposed soil bottom. There were two reasons for this type of construction. The obvious was it was less expensive to build because of less excavation and foundation walls, another was wood framed floors made more comfortable living spaces and concrete floors were not very popular due to the cold, hard surface. A crawl space provided a natural insulating air barrier between the ground and living space. The idea was to have an air space sealed from the outside not to let air pass to retain the heating and cooling. Another method was to have this crawl space vented to outside air to prevent moisture, mold and mildew.

Crawl spaces are still used in new houses but are constructed differently. A modern vented crawl space is usually 18″ to 30″ high, has masonry walls, perimeter insulation board, a vapor barrier under a concrete slab, exterior venting, and the floor joists are insulated with fiberglass insulation with a vapor barrier. This type of crawl space lets outside air pass thru to prevent moisture and helps retain the indoor temperature in the living space by installing insulation underneath the floor in between the joists. This is an accepted type of crawl space or basement in house construction as long as all of these items are in place. The concept of insulating a crawl space is to insulate the floor space as you would insulate the exterior walls to maintain an insulated envelope from outside temperatures or unconditioned spaces. For heated basements the walls should be insulated only, not the ceiling which is the floor of the living space. Insulating your basement or crawl space is an easy project to do it yourself.

Crawl Space – If your house is built on a crawl space and it isn’t constructed as the previous mentioned conditions, I would suggest that you update the crawl space by adding vapor barriers and insulating. Here are some tips for the do it yourselfer.

1. Repair and patch holes & cracks in the exterior foundation wall to prevent water from leaking in.

2. Check exterior drainage at the crawl space foundation and grade away from the house.

3. Add vents to exterior for air exchange, after adding vents run a portable fan for a couple of days to remove moisture before pouring slab.

4. If there is no concrete slab in the crawl space – first lay down a vapor barrier (4-6 mil polyethylene sheet material) on top of the exposed soil overlapping joints 6″.

5. Install rigid foam insulation board (usually 2’x8′) flat around the perimeter.

6. Pour a concrete slab 2″-3″ thick to cover vapor barrier on floor.

7. Optional is adding rigid insulation board to the interior of the foundation walls.

8. Insulate with batts of fiberglass insulation rated R13 or higher.

9. Use insulation that has kraft paper vapor barrier adhered to it and install with the vapor barrier up towards living space.

10. Use joist wires to hold insulation in place (there is no place to staple as the paper side is facing up, towards heated space)

11. Insulate any pipes or ducts in the crawl space.

Tools needed to do the Job – Do It Yourself Homeowner

1. Hand tools – tape measure, utility knife, steel framing square for cutting guide, hammer, staple gun

2. Misc. – dust masks, gloves, eye protection, insulation, plastic vapor barrier,

Insulating a Basement – insulating a basement is an easy project for a do it yourself homeowner or handy person. The basement walls should be insulated to help save on heating costs. If you are planning on finishing your basement now is the time to decide on a method of insulating. If you are going to stud frame out the exterior walls of the basement, install fiberglass insulation between the studs. Another method is to apply rigid foam board insulation directly to the interior of the masonry foundation wall before you install the framing. If the basement is temperature controlled there is no need to insulate the ceiling as this is the living space above and that area is already conditioned. In new construction rigid foam insulation can be applied to the exterior of the foundation walls before back filling takes place. Properly insulating a crawl space or basement will save money on home heating & cooling costs and make your home more comfortable.