Crawl Spaces – What, Where, and Why Insulate Them

How To Winterize Your Crawl SpaceCrawl Space Winterizing Before and After

There are some important reasons why you should insulate the crawl space under your home. Warm floors in your house can change the comfort levels keeping your feet nice and toasty. There might be pipes and duct work running through the space. If the area is winterized, the efficiency of the heating and air conditioning ducts will increase keeping the air inside the ducts the correct temperature from the furnace to the vents. Also true with the water pipes, the water inside the pipes will maintain the temperature all the way to the faucets.

So, what are crawl spaces? They are low or narrow open spaces beneath a portion of a home that gives access to wiring and plumbing for repairs and maintenance. There are two basic ways to go about insulating crawl spaces. Depending upon if there are pipes and ducts in the area. The process of winterizing the crawl space is easy enough for the DIYers, or a insulation contractor could be hired, either way, the project is straight forward.

Identifying The Area

Take a assessment of the crawl space. To get the correct supplies for the job, look in the area. Does the crawl space have pipes and ducts running in it? If so, you will need to insulate the walls. If not, the floor above will need to be insulated. Does the ground of the space have polyethylene sheeting (plastic)? If not, you will need to put some down.

This step-by-step guide will be broken up into two sections, with pipes/ducts and without.

How to Insulate Crawl Space with Pipes and Ducts Using Fiber Glass

Materials Needed

  • 10 or 12 mil polyethylene sheeting.

  • Pieces of wood or furring strips.

  • Several rocks, bricks, or boards.

  • Fiber glass insulation.

  • Spray expanding foam and/or caulk.
  • A knife to cut the insulation.

  • Nails and a hammer.

Step 1

Cover the ground with the polyethylene sheeting. Unroll the sheets in a overlapping fashion by 12″ or more. Then use rocks, bricks, or boards to hold the plastic in place.

  • Doing so will prevent ground moisture from entering the crawl space and  rising to the flooring above, causing mold or wood rot.

Step 2

Next, if the crawlspace walls or foundation have any vents, close them so insulation can be placed over them. Seal them if necessary.

Step 3

Seal any openings or cracks heading inside the house. Use expanding foam if gap is bigger than 1/4 inch. It is a good idea to caulk the band joist between the floor joists for a more air tight seal between the crawl space and the room above.

Step 3

Measure the distance from the top of the band joist (between the floor joist) down the wall extending two feet out along the ground. Multiply by the wall perimeter to get the number of square feet of insulation you’ll need.

Step 4

Cut the strips of fiber glass insulation to the appropriate length.

Step 5

Fasten each strip to insulate the band joist at the top of the wall by nailing a furring strip over the insulation. It will now hang down the wall and extend two feet onto the floor resembling an L shape.

Step 6

Use boards as necessary to hold the insulation in place on the ground without unnecessarily compressing it.

How to Insulate Crawl Space With Pipes and Ducts Using Rigid Foam Board

Instructions from homeguides.sfgate.com. This method is the preferred way of insulating your crawl space.

Materials Needed

  • 6 mil polyethylene sheeting.

  • Construction adhesive (Liquid Nails or similar).
  • Expanding foam insulation.

  • Rigid foam board.

  • A knife to cut the insulation.

Step 1

Measure the width and height of each wall in the crawl space. Multiply the results for each wall to determine the square footage. Add 10-percent to allow for errors. Use these numbers to order the proper amount of the rigid foam insulation product of your choice. Each sheet is generally 8 feet long by 4 feet wide, or 32 square feet.

Step 2

Measure the width and length of the crawl space itself (not the walls). Determine the square footage and add 10-percent. Add this result — which is the size of the crawl space floor — to the crawl space wall footage. Use this to determine the proper amount of vapor barrier — 6-mil polyethylene (plastic) sheeting works well — you will need.

Step 3

Hold an end of the plastic sheeting against the far end of the first crawl space wall. Spread the plastic the length of the wall, pulling it 2 or 3 feet past the wall end, to measure the length needed. Disregard the excess hanging down on the bottom — as long as it overlaps the crawl space floor at least 1 foot, it’s adequate. Cut the plastic with a pair of sheers. Measure and cut plastic for each wall similarly.

Step 4

Run generous beads of construction adhesive down each crawl space wall, working one at a time, spacing the squiggly-shaped beads every 8 to 10 inches. Immediately position the matching piece of plastic sheeting over the wall, ensuring it is higher than the wall, trailing over the floor, and extending on to the walls on either end. Press the plastic in place, running a hand over it to bond it completely.

Step 5

Adhere the plastic to the next, and each remaining wall, following the same procedures. Smooth out the excess material at the ends before layering the next wall’s material over top. Taking the time to do this and ensure overlapping joints will ensure an air- and moisture-tight installation.

Step 6

Cut each sheet of rigid foam insulation to fit the crawl space wall height. Use a straightedge and a utility knife to slice through the insulation, then snap the board along the cut line to get a precise break. At the end of the wall, cut the board to fit the remaining gap.

Step 7

Spread a water-based mastic or other adhesive approved for use with foam insulation across the area where the first sheet of insulation belongs. Depending on the product, you may have to trowel the mastic in long, broad strokes across the wall, or use a caulk-like product and apply squiggly streaks every 8 to 10 inches. Immediately press the insulation in place, following the manufacturer’s instructions if it specifies to pull the insulation away again before repressing it to the wall to set it. Install each sheet similarly, pushing each tight to the last.

Step 8

Cut small pieces of rigid foam to fit in between the joists around the perimeter of the wall. Glue and install the insulation. Follow with a measure of expanding foam insulation, which will seal any small gaps as well as help hold the insulation in place. Spray additional expanding foam insulation in any other breaks in the thermal barrier, such as around cable or pipe entrances.

Step 9

Spread the remaining plastic vapor barrier across the crawl space floor. Overlap rows as needed, extending the plastic a foot or two over the previous piece. Run the plastic up the exterior walls about a foot. Glue and adhere to create a strong bond.

 

How to Insulate Crawl Space Without Pipes and Ducts

Insulating the crawl space if it doesn’t have pipes and ducts involves putting insulation between the floor joists above. The space is not heated or cooled by furnace or air conditioner, then only the floor joists is insulated. There are specific insulation made for crawlspaces. Talk with the sales person to make sure you purchase the correct one.

Materials Needed

  • 10 or 12 mil polyethylene sheeting (plastic).

  • Spray expanding foam and/or caulk.

  • Fiber glass insulation.

  • Several rocks, bricks, or boards.
  • A knife to cut the insulation.

Step 1

To prevent drafts, caulk and seal around the band joists. Do the same around plumbing, wiring, vents and other penetrations.

Step 2

After the band joists are sealed, measure and cut pieces of insulation to fit snuggly between the joists against the band joists. Don’t compress the fiber glass. It will reduce the insulating power.

Step 3

Start putting insulation between the joists. Be sure it reaches all the way back to each joist run. You want complete coverage underneath the house. Fit insulation around any pipes, duct work, or wiring being careful not to compress the fiberglass. You can insulate around cross braces by cutting  and pushing it between the spaces. Do not leave any gaps or spaces between the insulation pieces. You may need to cut insulation to fit narrow joist spaces.

Step 4

Once the insulation is installed, use metal insulation hangers or nylon straps to hold the insulation against the subfloor. It is important the insulation stays in contact with the subfloor above to work properly.

Step 5

The last step is to line the ground with polyethylene sheeting with a 1 foot overlap. Use boards or rocks or bricks to hold the sheeting in place.

This project will add warmth and energy savings year after year. And, can be done in one weekend.

Bookmark the permalink.

Comments are closed.