Underfloor Insulation is a great way to insulate and protect you and your family.
1. During the early phases of construction, meet with the mechanical subcontractors (plumbing, electrical, and heating/ cooling) to inform them of the importance of keeping the space between 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 protection against freezing, supply plumbing may be located within the underfloor insulation. The best approach is to run supply plumbing together in a few joist spaces. The underfloor insulation can be split and run around the piping.
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. Select insulation levels in accordance with the International Energy Conservation Code or the DOE Insulation Fact Sheet.
4. underfloor insulation batts with an attached vapor barrier are usually 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 that may serve as passageways for cold air to flow between the insulation and the subfloor. The batts should be cut to the full length of the joist being insulated and slit to fit around wiring and plumbing. Insulate the band joist area between 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. 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 making sure the crawl space is dry and all construction materials have dried out.
Underfloor Insulation Truss Floor Systems
Instead of batt insulation, a better approach is to install netting or rigid insulation to the underside of the floor trusses and filling the space created between the netting or insulation and subfloor with a loose-fill insulation.
Are Crawl space Vents Necessary?
Most building codes require crawl space vents to aid in removing moisture from the crawl space. However, many building professionals are now recognizing that an unvented crawl space (or closing crawl space vents after the crawl space has had time to dry out after construction) is the best option in homes using proper moisture control and exterior drainage techniques for two reasons. First, ventilation in the winter is undesirable in order to keep crawl spaces warmer. Second, warm, moist outdoor air brought into the crawl space through foundation vents in the summer is often unable to dehumidify a crawl space and, in fact, can lead to increased moisture levels in the crawl space. For example, a crawl space kept cool by the ground in the summer may have a temperature of 65°F and 90% relative humidity (RH)—the dew point temperature of the air is 62°F. The dew point of outdoor air at 90°F and 60% RH is about 74°F. Thus, outdoor air brought into the crawl space will actually increase the moisture level until water condenses out on cool crawl space surfaces such as floor joists, foundation walls, and air-conditioning ducts. As framing stays moist, mold grows and dry rot develops.
Build In Radon Resistance
Radon is a radioactive gas that occurs in some soils. It can enter a home through the foundation and floor system. If it occurs in significant concentrations (greater that 4 picocuries per liter), it may pose a severe health risk to the home occupants. To guard against radon problems:
• Install a sealed, continuous layer of 6-mil polyethylene over the crawl space floor.
• Install a plastic tee below the polyethylene that protrudes through the polyethylene.
• Install a vertical 3-inch plastic pipe from the foundation to the roof through an interior wall.
• Connect the tee to the vertical 3-inch plastic pipe for passive mitigation.
• Have an electrician stub-in a junction box in the attic.
• Test the bottom conditioned room for radon with an EPA-listed radon test kit, or hire a qualified technician. If the house has a high radon concentration, install an active radon mitigation system by attaching a small blower to the plastic pipe in the attic to expel the gases to the outside.
• If radon levels are especially high (over 25 picocuries per liter), consult with local radon experts.