Community associations, building owners, engineers, contractors and property managers deal with the constant battle of keeping water out of the building envelope, but sometimes the water that causes stains, mold and decay actually originates from within the building envelope. The cold temperatures of the winter months combined with specific interior conditions will result in excessive condensation. The condensation may be in the attic, basement and crawl spaces or inside wall cavities. Deficiencies in the original construction or recent reconstruction of exterior wall cavities, basements, crawl spaces and/or roofs /attics can exacerbate the conditions resulting in excessive condensation conditions and potential for damage and mold development. Sometimes, the conditions may be seen but many times the condition and subsequent damages may be hidden from view and worsen with each passing winter season, escalating repair costs.
Condensation will also form on cold surfaces (such as single window panes and aluminum window frames with no thermal break or un-insulated walls) as warmer moisture saturated air contacts the cold surface, causing the air that is in contact with the window to cool. These conditions can also result in damage to insulation, structure, or interior finishes and mold growth.
Aside from proper construction methods and materials, the most essential aspect of preventing moisture damage to a building from condensation is to keep indoor relative humidity at effective levels during the winter season. Humidity levels consistently below 30% may cause respiratory problems and shrinking of wood furniture, flooring or trim, readings of 30% or higher appear to prevent or certainly reduce these problems, however higher humidity levels begin to create the potential for resulting in condensation.
Condensation is the process of water vapor in the air turning to liquid water. Condensation of water vapor occurs when the temperature of the air is lowered to the point that the air cannot hold any more moisture (the Dew Point). At this critical temperature, the water vapor will turn to liquid water. In general terms, the interior warm air contains moisture that will migrate, by diffusion to the lower pressure or colder air (exterior). Periods of some condensation are a normal occurrence and typically will not result in damage as the areas will dry out. However, the warmer or more moisture-laden the air is and if it is consistent, the more diffusion that occurs and with that more and continued condensation.
When indoor heat and humidity becomes elevated during the winter season, condensation conditions begin to appear. It is difficult, even with proper wall construction and vapor retarders to construct a building that will not have condensation problems when indoor humidity exceeds 40 or 50 percent without incorporating special design aspects of mechanical equipment including de-humidification.
Normal household activities such as cooking, showering or bathing, washing clothes and dishes, drying clothes, even breathing and perspiring can raise the humidity level in a home. A typical family of four converts three gallons of water into water vapor per day. It takes only about six pints of water to raise the relative humidity of a 1,000 sq. ft. home from 15 to 60 percent so any excess of the activities listed above can elevate the moisture in the air even more.
To reduce the potential for condensation and avoid the problems of excess moisture it is necessary to limit or control the amount of water vapor in the house. This can be accomplished by modifying lifestyle activities and/or by using mechanical means such as exhaust fans, dehumidifiers.
To reduce moisture vapor production within the home the following can be implemented.
Building codes address the amount of insulation to be used and the use of vapor barriers and vapor retarders however; specific design analysis is not a requirement. While building codes also address ventilation and moisture control in general terms, they lack specifics with regard to varying construction or conditions. It is critical that each specific condition should be properly analyzed.
In general terms the following information typically will apply to Northeast construction.
Walls: As the most basic and general rule, a vapor retarder should be installed on the warm side of the insulation during new construction or significant rehab projects. This vapor retarder will limit the amount of interior water vapor that passes into the wall cavity. This is typically accomplished by installing paper faced insulation upon original construction. Although not a code deficiency, the paper backing on typical blanket insulation is technically a vapor retarder, but the ends do not overlap each other over the edge of the studs for it to be completely effective. It is also difficult to provide coverage of wall framing, window and door framing with this type of vapor retarder. A more effective vapor coverage may be the installation of wide sheets of polyethylene inside the wall with precise cutouts for windows and outlets.
The designer should analyze the wall cavity to determine whether the assembly is susceptible to condensation. There are many variables that affect this potential. Different systems will react differently and need to be investigated. The type of materials and their respective R- value, permeability rating, thickness and even location within the cavity are all factors that can affect the potential for excessive condensation to occur. The size, type and layout of the interior environment also contain factors that should be considered.
A change in any of these variables can affect potential for condensation dramatically. For example, a change in a building façade from vinyl siding to a stucco system may create future condensation problems if the above discussed variables are not analyzed. Additional vapor barriers or other products may be necessary.
Attics: Attics should be properly vented and insulated. The temperature of the attic space should be consistent with the exterior temperature. Flat roofs may require a similar analysis as with walls as discussed above
Crawl spaces: Crawl spaces should be properly vented including, as needed exhaust fans and/or sump pump systems to reduce moisture and protect framing.
Basements: Dehumidifiers and proper wall cavity construction is needed if finished space is desired.
The construction, use and maintenance of a building can have a significant impact on the humidity levels and condensation issues that may occur. Condensation was not much of a problem in pre-WWII construction, as the 'loose' or energy inefficient construction allowed for the flow of air and humidity in and out of the building. With new, more efficient construction methods, more appliances and living habits that release water vapor into the home, condensation has become more prevalent and the damages and mold growth that go along with continued wetting have become an issue.
It is important to properly evaluate an existing condensation problem as well as to be sure to consider the use of different materials when constructing or reconstructing a building.
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