Best Insulation to use for Basements and Crawlspaces

Due to their underground environment, basements and crawl spaces have different insulation requirements than the house above. Moisture is the primary consideration in developing either a basement or crawl space insulation strategy. Excess moisture can cause mold, mildew, odors, decay, fungus growth and wood rot.

Moisture penetrating the basement and crawlspace can come from a multitude of sources:

• Construction materials that must dry before the basement is sealed
• Interior diffusion from humidity in warm indoor air
• Hydrostatic pressure against the foundation wall from rainfall, snow melt or irrigation creates exterior diffusion
• Air infiltration bringing moisture in with it
• Capillary rise wicking moisture up from the soil below
• Groundwater leakage through the foundation

The underground environment of walls below grade presents unique challenges. The moisture content in soil below three feet deep is almost always higher than the moisture content of the air inside. This difference in vapor pressure causes moisture to be driven from the soil into the basement or crawl space interior by diffusion through the wall. A significant amount of moisture from the soil below the slab will also wick upward into the basement through the slab or directly into the crawl space.

Condensation is also a significant problem in basements and crawl spaces. Underground soil temperatures can be much colder than either the outside air or the indoor air in the basement. The warmer air of the basement constantly expands. When this warm air reaches the cooler surface of a wall next to the ground, condensation will occur on the interior of the wall. Any interior insulation will be subject to potentially large amounts of moisture driven from both the exterior and the interior depending on the season.

Air infiltration can be a major source of moisture in a basement. A lot more water vapor can move through a very small opening where the vapor pressure is greater on the exterior than can move through the wall surface by diffusion. Air-transported moisture can quickly lead to mold, mildew and decay in interior wall assemblies.

The insulation system must prevent warm inside air from reaching the cool foundation wall to prevent condensation. Reflective insulation is an effective interior air barrier. In addition, reflective aluminum foil insulation is moisture tolerant and does not support mold, mildew or fungus growth or lose thermal effectiveness when wet. Reflective insulation is always installed with an air space so moisture on interior walls can evaporate. Many use reflective insulation for insulating exterior basement walls.

Fiberglass Insulation or blanket insulation should not be used in a basement. "Framed stud walls on the basement interior with batt insulation between the studs and a vapor barrier over the studs was used for many years as the building standard but is no longer recommended due to excessive problems with mold, decay and odors." (Yost and Lstiburek, 2002)

To maintain its thermal effectiveness, fiberglass insulation cannot be exposed to moisture. Moisture will degrade the insulation R-value of fiberglass batts and promote mold and mildew which lower indoor air quality. Installing a vapor barrier over the interior of fiberglass insulation will prevent the foundation walls from drying to the interior, a problem with mitigating capillary rise, groundwater leakage and construction moisture. Batts with no vapor barrier will not be effective either as interior humidity will still cause loss of insulation R-value.

Basements can be insulated on either the interior or the exterior. Basements with water leakage, dripping and other moisture problems in a masonry, rubble or brick foundation must be insulated from the outside. For most locations, R-11 building insulation is recommended for both interior and exterior installation on masonry walls and R-19 for wood walls. In the coldest climates, R-19 to R-30 building insulation is recommended.

Prodex Total Insulation should also be installed under the basement slab. Reflective insulation can be used to provide a thermal break, a vapor barrier, and a radon barrier when installed under the slab on top of the gravel drainage bed. Insulation under the slab will also make the basement floor warmer. To create a vapor barrier, the insulation should be sealed to the foundation wall.

Reflective Insulation is an effective 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.

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.

If you do not intend to use the basement as an extension of your living space, it can be insulated in the same manner as a crawl space. Proper insulation of your crawl space will:

• Keep the floors above noticeably warmer
• Reduce air infiltration and drafts
• Save energy and money by keeping heat and air conditioning inside
• Minimize problems with condensation, wood rot, mold and mildew
• Provide waterproofing
• Seal entry paths against termites
• Control radon infiltration

A poorly insulated crawl space can account for 15 percent or more of a building's total heat loss. For most geographic areas, crawl space walls should be insulated to R-19 while the floor over an un-insulated crawl space (or crawl space ceiling) should be insulated to R-25.

Reflective insulation is most effective against downward radiant heat transfer making it the builder's choice for crawl spaces as a radiant barrier. Heat radiating downward from your floor into the crawl space will be reflected back inside, saving energy and 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 combined in one product.

Today's building codes call for un-vented crawl spaces. Crawl space walls should only be 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. Crawl spaces are most commonly insulated on the ceiling and floor and not the walls.

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 Prodex Total Insulation as vapor barrier under the floor insulation and also on the floor of the crawl space 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 by blocking their entry path.

Experts recommend installing a vapor retarder, like Prodex Total 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. Prodex Total Insulation (A vapor retarder) should also be used as a groundcover to create a radon barrier with the edges tightly sealed to the interior face of the crawl space wall.

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