Vapor Barrier Basics
What is a Vapor Barrier?
A vapor barrier is material that prevents any type of gas from passing through it. There are various strengths of vapor barriers and the most effective ones allow no gases (vapor and heat) to penetrate while less effective barriers can leak like a sieve – allowing almost any types of gas to pass through into your home. The metric used to rate these materials is permeability, with 0.000 permeability being the best.
Actual vapor barriers are usually made out of some sort of material like aluminum or plastic which will normally not allow any gasses to pass through. More commonly you will find vapor retarders, however, which are not technically impermeable, and will allow small amounts of gas to pass through them. However, these amounts are normally negligible.
Why Use a Crawl Space Vapor Barrier?
The soil under your home is constantly emitting water vapor into the atmosphere. Under normal conditions, the vapor will dissipate quickly into the atmosphere. But water vapor can become trapped under the crawl space of your house and cause problems with your sub-floor construction, especially if you live in an area that receives high moisture levels yearly. And even arid areas have their wet seasons during which your home could be vulberable to ground water vapor and condensation problems. Most houses with crawl spaces will also have some sort of crawl space ventilation, but these are highly inefficient and are often not enough to stop water vapor from condensing on wood structural parts of your house, which will eventually cause wood-rot and diminish the value and overall structural stability of your house. A crawl space barrier is an effective tool in combating mildew, mold and wood-rot.
Crawl space vapor barriers can improve your home’s energy usage in two ways: by insulating your home from heat and cold and weatherizing your home against the elements. Just like the insulation in your walls improve your home’s energy efficiency, insulation in your crawl space will prevent the outside air from penetrating through the floorboards in your home. Weatherizing your crawl space stops convective energy (air) from entering your crawl space – just like leaving a window cracked open, small cracks beneath your home can let in air through your floor boards. A high-performance vapor barrier can almost completely eliminate any ground water vapor from seeping into the open space under your home and through your floor boards into your house.
A vapor barrier can also be a valuable tool for homes that have concrete slab construction, with no open area or craw space beneath the house. Water vapor can condense on the slab of your house and eventually make its way through the concrete and into parts of your home more sensitive to condensation and water issues. It is a good idea to install a water-vapor barrier underneath your home’s concrete slab in order to insure that water-vapor and condensation are not a problem.
In addition to protecting your home from outside forces which may reduce the value of your home, a crawl space vapor barrier can also help you save on energy costs. In cold climates, using a vapor barrier in addition to regular insulation can make your house more airtight and help keep warm air from escaping outside. Similarly, in a hot climate, the barrier can help keep your electric bill lower, by not allowing cool air to escape through your crawlspace to the outside.
A crawl space vapor barrier can be an effective tool in the life of your home, boosting longevity of sensitive materials, as well as boosting the energy efficiency of your home.