How to Insulate a Subfloor Crawlspace

Insulating a subfloor crawl space will help cut damp drafts rising through your floor and save you money on heating and cooling bills. If the crawl space is easily accessible, insulating the subfloor is a straightforward task that will significantly improve the comfort of your home.

Difficulty: Challenging

Instructions

Things You'll Need:

• Measuring Tape
• Polyethylene sheets
• Pressure-treated wood furring strips
• Nails
• Hammer
• Respirator mask
• Safety goggles
• Gloves
• Fiber glass batt Insulation
• Rigid foam board insulation
• Construction adhesive
• Utility knife
• Straight edge

1. Measure the subfloor area that you want to insulate as well as the space between the floor joists. Check local building codes for requirements on crawl-space insulation in your area and incorporate these into your plan.

2. Clean the underfloor crawlspace, removing cobwebs and debris. This will help make installing insulation easier and quicker. Treat your subfloor framing to guard against borers and termites.

3. Roll out polyethylene sheets on the crawl-space floor and lap them 12 to 24 inches on the long edges. Extend the polythene sheeting up the walls, about 12 inches if possible, and tack it in place using pressure-treated wood furring strips or heavy-duty tape.

4. Nail pressure-treated wood furring strips perpendicular to the floor joists, 18 inches apart. The furring strips should be close enough together to hold insulation in place and wide enough apart to push insulation between the floor joists.

5. Install fiber glass batts snuggly between the floor joists and around the perimeter of the floor. Wear a mask respirator, safety goggles and gloves when handling fiber glass batt insulation. Check that the batt insulation is not bunched up between the joists and that there is no gap between the top of the insulation and the underside of the floor above.

6. Fix fiber glass batts or rigid foam board insulation to the crawl space walls, using nails or construction adhesive. Cut the batts or foam insulation to fit using a utility knife and a straight edge.

References

• Air Seal and Insulate with ENERGY STAR
• Insulation

Resources

• ENERGY STAR Insulation Products

[maggiemay55]

on 10/28/2009 Questions:
Is this method for a ventilated or unventilated crawl space? What is the thickness the polyethylene sheets should be? What product do you treat the subfloor wood beams with to repel borers and termites, and is that a job for the professionals? In step 6, fixing the batt insulation to the crawl space wall, how far up the walls do you go -- all the way to the wood beams of the floor or only over the 12 inches of polyethylene sheeting?