| Controlling Moisture |
Controlling Moisture
Most people feel comfortable when they breath air that contails 40 to 60 percent relative humidity. Some suffer discomfort in the drier winter air. To compensate, they may keep a tea kettle on top of a wood stove or run a humidifier. While additional moisture may be more comfortable, it can be a hazard to an insulated house. With escape routes sealed, the warm moist air migrates through ceilings and walls until it is cool enough to condense. The result is moist insulation that loses efficiency, causing wood to decay and outside paint to peel.
There are ways to tighten up a home without suffering dry air in the winter. The natural moisture given off by bathing, showering, and household plants usually is enough to ensure comfort. There are some ways to ensure wholesome inside are while keeping moisture out of the stucture.
- Do not use humidifiers to add moisture.
- Do not store green firewood inside
- Make sure clothes drier is vented to the outside
- Install a vapor barrier when working with new construction or when tearing off the finish material of walls or ceilings to add insulation
- Provide controlled ventilation in the form of individual exhaust fans or a central ventilation system.
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If you find wather dripping off the insides of windows during winter, it is a good indication that the indoor moisture level is too high. An inexpensive hygrometer provides a more exact reading of the level. If the moisture level is too high reduce it by heeding the measures suggested earlier. The next line of defense is to provide the house with adequate ventilation. Finally, use the opportunity when remodeling or adding insulation to install vapor barriers that are effective for your particular climate.
Installing Vapor Barriers
More moisture passes through cracks and gaps by way of convection than by diffusion through the materials, so the first line of defense is sealing up airways by weather stripping windows and doors, caulking cracks and installing air barriers beneath the siding. Once the flow of air is blocked, the passage of moisture through the materials themselves must be stopped. A vapor barrier, placed between the wall and ceiling and the side expose to moist air, is used for this purpose. The material can be separate sheet of moisture-impereable material, such as polyethylene or the foil facing of insulation.
Vapor barrier are necessary in cold and mixed climates and recommended in warm climates if the house is air conditioned for large portions of time. Two things are important when installing vapor barriers.
- The marier must be on the proper side of the heated space
- It must be continous to be effective
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Continuity is hard to achieve in existing construction. Even if the plaste or drywall is removed fromoutside walls, it may not be possible to extend the vapor through intersecting interior walls and floors. Tejse intersections become the weak link in an other wise moisture tight system. Each project is different so make the vapor barrier as continuous as possible. If it not possible to provide a continuous vapor barrier or one that is nearly continuous by using plastic sheeting, the next best thing to do is to thoroughly caulk around electrical boxes, window and doors, and edges of new drywall.
Cold and Mixed Climates
In cold climates where moisture problems are most severe during the winter, the vapor barrier is installed on the inside of the wall.
Between the cold and hot climates there is a twilight zone where both winter heating and summer cooling are about equal in importance. The best placement for a vapor barrier in this case is unclear. Some experts suggest using the same strategy used in cold climates (with vapor barrier on the inside) because moisture problems are likely to be worse during the winter than in the summer. Most agree however, that air barrier (house wrap) on outside is important to block airborne moisture.
Warm Climates
The air/vapor barrier is place near the outside of the wall in the hot humid areas of houses that are air-conditioned for most of the year. Check with an air conditioning specialist or your local building department for advice on the product that best suits you home and climate. Unlike those in cold climates, crawl spaces found in warm climates must be ventilated.
