Dealing with Moisture Buildup | |
When winter arrives and temperatures plunge, you might think the movement of heated air would no longer cause problems in attics. But that's not true. With seasonal changes, the conditions just reverse. Heat doesn't travel from an attic into the living quarters. Instead, heated indoor air travels from the home into the attic along with moisture. The problem is especially acute in homes with electric heating. Most of these homes were built since the mid-1970s, using advanced insulation materials and methods. As a result, most are "tight," allowing minimal infiltration of outside air. In addition, electric heat sources do not require air for combustion, so another common source of outdoor air has been eliminated. The positive side of these super-insulated homes is, of course, the greater energy efficiency. But because cooler, drier outdoor air is kept out, the indoor air holds greater amounts of moisture. Problems arise when the warm, moist air from the living quarters moves toward the attic, where the air is cooler and drier. That moist air is drawn to the attic in two ways. The first is through a process called "vapor diffusion." It's a process in which water vapor naturally travels from high-humidity conditions to low-humidity conditions, in our example, from the living quarters into the attic. The force of vapor diffusion is so great that moisture even travels through building materials such as sheet rock (TM). Even vapor barriers, for all their effectiveness, cannot totally stop this process. The second way moisture travels into an attic is by air moving through openings cut into a vapor barrier. Such openings are commonly found, for example, at recessed ceiling boxes and attic entries. The problems start when moist air hits cooler rafters trusses and roof sheathing. The moisture condenses as water droplets or frost. Eventually, the condensation drips on the insulation below. If too much water soaks into the insulation, its volume can be compressed and its effectiveness reduced. The sequence of events that follows is predictable: greater heat loss leads to colder rooms, colder rooms lead to a greater need for heat, greater use of the furnace leads to higher energy bills. But that's only the immediate problem and its consequences. As with heat buildup, moisture buildup has long term effects. That's because not all the condensing moisture drips into insulation. The structural elements of the house absorb some, leading to wood rot and the deterioration of roofing materials. Other moisture is likely to soak into the attic floor and eventually into ceiling materials, causing water stains and paint damage in the rooms below. Ventilation Solves Attic Moisture Problems Although the problems of attic heat and moisture have different causes, they share a common solution: a high-efficiency ventilation system that allows a uniform flow of air to sweep the underside of the roof sheathing. In warmer months, such a system exhausts hot air from an attic; the colder months, it exchanges warm, moist air with cooler, drier air. In both cases, the result is the same: more comfortable living quarters, less energy use, less damage to a home. Source: Air Vent Inc. A Certainteed Company Reprinted with permission. |