contents 1. Benefits of Crawl Space Insulation 2. R-Values 3. Thermal Insulation 4. Condensation 5. Radon 6. Installation 7. References

The US Department of Energy estimates that a poorly insulated crawl space accounts for at least 15 percent of a building''s total heat loss and even more if the crawl space is completely un-insulated. Proper insulation in your foundation crawl space will keep the floors above noticeably warmer as well as save energy and money. Crawl space insulation will provide thermal and vapor control; waterproofing; and mold, mildew, odor, decay, termite, and radon control.

• Warmer, more comfortable floors in winter - reduce air infiltration and drafts
• Lower utility bills - keep heat and air conditioning inside
• Moisture control - insulation can minimize problems with condensation, wood rot, mold and mildew
• Protect against radon infiltration
• Seal entry paths against termites

Insulation is rated by its ability to resist both conductive and convective heat flow in units called R-value. R-value gives the insulation resistance per inch thickness of a material. Construction materials with higher R-value ratings are more effective insulators than materials with lower ratings for the same thickness. For example, convective heat will flow through an R-12 insulated wall only half as fast as through an R-6 wall.

Click here for an article on insulation R-values.

Insulating to the recommended US Department of Energy R-value for your climate will provide the optimum balance between money spent on insulation versus money saved in un-necessary energy use and also provide optimum indoor comfort levels. For most geographic areas, crawl space walls should be insulated to R-19 while the floor over an un-insulated crawl space should be insulated to R-25.

You can determine the correct R-value for your crawl space based on the type of fuel you use and your zip code using the Department of Energy''s R-Value Recommendation form.

Click here to use the easy online calculator.

Heat moves through between floors and crawl spaces by a combination of radiation, conduction, and convection with radiation being the dominant method of heat transfer. Radiation accounts for 65-85 percent of all heat transfer through floors. Reflective insulation is an effective barrier against radiant heat transfer because it reflects back almost all of the infrared radiation striking its surface and emits very little of the heat conducted through it. Reflective foil insulation products also incorporate trapped air spaces using foam or plastic bubbles as part of the system to retard the convective flow of heated air the same way mass insulation does.

Reflective insulation is primarily effective against downward radiant heat transfer. This means that heat radiating downward from your floor into the crawl space will be reflected back inside, saving energy on maintaining constant room temperatures. The most recent advance in crawl space insulation by far is using reflective insulation as a vapor barrier, radon barrier and thermal insulation in one product.

Benefits of using reflective insulation include:

• High R values up to 14.5 Details
• Reflects up to 97% of downward radiant heat
• Use stand alone or with rigid insulation
• Vapor barrier - moisture-proof
• R-value is unaffected by humidity, unlike fiberglass
• Radon barrier
• Air infiltration barrier
• Non-toxic, non-carcinogenic, no fibers to inhale, no chemicals to off-gas
• Can be glued, nailed, stapled or sewn

Click here for a comprehensive article on reflective insulation.

Proper insulation is part of the overall moisture control strategy in a crawl space. Insulation technique depends on whether you have a vented or un-vented crawlspace. The US Department of Energy recommends an un-vented crawl space for all new construction. A vented crawl space will allow winter cold air into the crawlspace often with a dewpoint that is lower than the crawl space air causing condensation.

Condensation in a crawl space is controlled by strategic use of vapor retarders or vapor barriers like reflective aluminum foil. A vapor barrier slows the rate at which moisture moves through a material. The goal in a crawl space is to keep the moisture in the soil from rising into the building where it can cause rot, mold, mildew, odors and fungus growth.

Use a vapor barrier under the floor insulation and also on the floor as ground cover in a vented crawl space. In an un-vented crawl space, the vapor barrier is used only on the floor. Installing a vapor barrier as ground cover can also help deter termites.

Click here for an article on condensation and vapor barriers.

Reflective insulation can provide a barrier against the upward migration of radon gas through joints, cracks and other openings in the building foundation into your living space. Radon is a radioactive gas found in soils, rock and groundwater. It is formed by the natural decay of radium and uranium isotopes. Radon levels vary depending on the geologic makeup of your location. Radon is naturally emitted from the ground where it is diluted to an insignificant level by the atmosphere. Inside a sealed and insulated building, radon can concentrate into unnaturally high and potentially dangerous levels.

The US Department of Energy has found that radiation from high levels of radon decay in enclosed spaces is responsible for the above-normal incidence of lung cancer found among miners. According to the US Environmental Protection Agency, radon is the second leading cause of lung cancer. Levels of radon in indoor air should be below 4 pCi/L.

Your home can act like a vacuum drawing radon up through the crawl space in two ways. First, the air pressure inside is usually lower than pressure in the soil around the foundation. Second, warm air will rise to leak out through attic vents creating a small amount of suction that can pull radon gas up through the crawl space.

Experts recommend installing a vapor retarder, like reflective insulation, as an underlayment between the crawl space and the first floor as a radon barrier. This layer will also function as a continuous air infiltration barrier. A vapor retarder should also be used as a ground cover to create a radon barrier with the edges tightly sealed to the interior face of the crawl space wall.

Installation methods differ between a ventilated and a non-ventilated crawl space. In a vented crawl space, the insulation is place below the floor joists in the ceiling. Do not use fiberglass between the joists as this leaves your crawl space exposed to thermal bridging through the wood. Fiberglass will also become wet from humidity or condensation and lose its insulating properties. Experts recommend a combination of rigid and reflective insulation installed over the joists. Any pipes or ducts between the joists will automatically be insulated this way and the reflective insulation provides the vapor and radon barrier.

Ceiling Method

• Staple insulation under the floor joists. Be sure to seal it well around the perimeter joist as close as possible from the top corner.
• Seal all the seams with aluminum tape.
• Install rigid foam board insulation over the reflective insulation to achieve higher R values.

Crawl space walls are only insulated if the crawl space is un-vented and the floor above the crawl space is un-insulated. While walls can be insulated on either the interior or the exterior, interior insulation is the preferred approach if you want to use the insulation to double as a vapor or radon barrier. If you use rigid insulation on the exterior, a layer of reflective insulation must still be used on the crawl space floor as ground cover.

Interior Wall Method

• Install rigid foam board insulation. This is optional. Reflective insulation can be used alone. Install reflective insulation horizontally, against the concrete wall over wood strapping every 16" with the asphalt felt behind it.
• Staple the reflective insulation with the foil facing the interior of the room at every 16" without overlapping the material.
• Seal all the seams with aluminum tape.
• Install the second wood strapping or stud perpendicular to the first one.
• Install drywall following the manufacturer''s recommendations.

Reflective Insulation with Rigid Foam Board Insulation Concrete Wall Rigid Insulation Reflective Insulation Wood Strapping (air space) or Studs Drywall

Reflective Insulation Alone Concrete Wall Asphalt felt behind the wood strapping Wood strapping (air space) Reflective Insulation Wood Strapping (air space) or Studs Drywall

Ground Cover

Reflective insulation should be used as a ground cover to retard water vapor and radon gas migration into the crawl space from the earth below. The US Department of Energy recommends a ground cover in all regions with 20 inches or more annual rainfall. All edges should be lapped 12 inches and both seams and edges should be taped. For additional radon protection, the ground cover should extend up the face of the wall. A barrier on the wall helps keep water that may leak through the wall confined to the underside of the vapor barrier on the floor.

US Department of Energy, "Insulation Fact Sheet, R-Value Recommendations for New Buildings", 1997.

Carmody, John; Christian, Jeffrey; Labs, Kenneth, "Builder''s Foundation Handbook", Oak Ridge National Laboratory, May 1991.