1. 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.

Run drain lines, electrical wiring, and ductwork below the bottom of the insulation so that a continuous layer of insulation can be installed.

For freeze protection, supply plumbing may be located within the insulation. 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. Seal all air leaks between the conditioned area of the home and the crawl space. 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. Obtain insulation with the proper width for the joist spacing of the floor being insulated. Complete coverage is essential. Leave no insulation voids. The batts should be installed flush against the subfloor to eliminate any gaps, which may serve as passageways for cold airflow between the insulation and 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. Insulate the band joist area between the air ducts and the floor as space permits. Use insulation hangers (wire staves) spaced every 12-18 inches to hold the floor insulation in place without compressing the insulation more than 1 inch.

5. The orientation of the vapor barrier depends on the home's location or climate. In most 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. Insulate all ductwork in the crawl space.

7. Insulate all hot and cold water lines in the crawl space unless they are located within the insulation.

8. Close crawl space vents after ensuring that the crawl space and all the construction materials are dry.

For insulating truss floor systems, it's better to install netting or foam board insulation to the underside of the floor trusses. Then, fill the space created between the netting or insulation and subfloor with loose-fill insulation.

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Information couretesy of EERE