If you are building a new house or having a major remodel done on your existing home, it will pay off in energy savings and increased comfort to have underfloor insulation installed. During the early phases of construction, the builder should inform all subcontractors (plumbing, electrical, HVAC, etc.) that they need to keep the space between the floor joists as clear as possible.

1. Have drain lines, electrical wiring, and ductwork run below the bottom of the insulation so that a continuous layer of insulation can be installed. If you live in an area with freezing winters, supply plumbing may be located within the insulation for added protection. The best approach is to run supply plumbing together in a few joist spaces. The insulation can be split and run around the plumbing.

2. All air leaks between the conditioned area of the home and the crawlspace should be sealed. High-priority leaks include holes around bathtub drains and other drain lines, plenums for ductwork, and penetrations for electrical wiring, plumbing, and ductwork (including duct boot connections at the floor).

3. Insulation batts with an attached vapor barrier are typically used to insulate framed floors. Make sure the insulation is the proper width for the joist spacing of the floor being insulated. Complete coverage is essential; there should be no insulation voids. The batts should be installed flush against the subfloor to eliminate any gaps, which could serve as passageways for cold airflow between the insulation and the subfloor. The batts also should be cut to the full length of the joist being insulated and slit to fit around wiring and plumbing.

4. Have the band joist area between the air ducts and the floor insulated as space permits. Use insulation hangers (wire staves) spaced every 12–18 inches to hold the floor insulation in place without compressing it more than 1 inch.

5. The orientation of the vapor barrier depends on the home’s location and climate. In most parts of the country, the vapor barrier should face upward. However, in certain regions of the Gulf states and other areas with mild winters and hot summers, it should face downward.

6. All ductwork in the crawlspace should be insulated.

7. All hot and cold water lines in the crawlspace should be insulated unless they are located within the insulation.

8. Crawlspace vents should be closed after ensuring that the crawlspace and all the construction materials within are dry.

For insulating truss floor systems, it’s better to have netting or foam board insulation installed to the underside of the floor trusses. Then, the space created between the netting or insulation and the subfloor should be filled with loose-fill insulation.

Get Pre-Screened Basement Drainage Help in Your Area

Information courtesy of EERE