BASEMENTS
This is the one area of insulation where we offer absolutely no options. We install closed cell spray foam and nothing else!! The reason for this is because nothing else should be installed here…EVER.
No one says it better when it comes to insulating your basement than Mike Holmes so this entire section is taken from his publications.
“no matter what, if you insulate your basement the same way you do an above-grade wall — using wood studs against the wall, with batt insulation in between and vapour barrier over that — you will have air movement and problems with condensation, and very likely, with mould” – Mike Holmes, excerpt from The Globe and Mail October 5, 2007.
The following information was taken from Mike’s website www.makeitright.ca.
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:
o Construction materials that must dry before the basement is sealed o Interior diffusion from humidity in warm indoor air o Hydrostatic pressure against the foundation wall from rainfall, snow melt or irrigation creates exterior diffusion o Air infiltration bringing moisture in with it o Capillary rise wicking moisture up from the soil below o 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. 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.