Ventilation in an attic is very important. It allows moisture that accumulates in the area to dissipate and also helps to reduce the heat buildup that normally develops during the summer months. Some of the moisture generated in the structure by bathing and cooking works its way up into the attic. If the area is inadequately ventilated, this moisture can eventually cause problems such as delaminating roof sheathing, water streaks on interior walls, peeling and flaking paint, and in severe cases some rotting of the wood framing. When walking around the attic, make sure that all vents are completely unblocked. Sometimes the homeowner blocks a vent opening (see FIG. 9-4) to cut down on the cold air entering the attic and reduce the heat loss through that opening. What he doesn’t realize is that he is creating a problem. If the attic is properly insulated, the heat loss through the vent openings is minimal. Of greater importance is the need for vent openings so that moisture can escape. Look around; you’ll be able to tell whether the attic is adequately ventilated.
Look at the roofing nails projecting through the sheathing. If you happen to be in the attic on a winter day when the temperature is around 20° F and the area is inadequately ventilated, you will find frost on the roofing nails. (See FIG. 9-5.) The frost that forms on the nails melts and drips onto the floor during the warmer periods of the day. Many droplets of water show up as circular stains on the floorboards and on top of the insulation. If you are in the attic during the warmer months, you’ll find rust stains on the sheathing near the nails.
When inspecting the attic, pay particular attention to the north slope of the roof. If the area is inadequately ventilated and plywood is used for the roof sheathing, delamination of the sheathing might be a problem. The northerly slope begins to delaminate before the southerly slope. Figure 9-6 shows an advanced stage of delamination as a result of moisture buildup in the attic. At this stage the entire roof sheathing and shingles must be replaced. The condition could have been avoided if the attic area had been adequately ventilated. Correcting an inadequately ventilated attic is relatively easy. All that is required is to increase the size of the existing vent openings (if there are any) or to provide additional openings such as roof vents, ridge vents, soffit vents, or a power ventilator. These vent openings can be used individually or in combination. The exact number of vent openings needed should be determined by a professional.
A power ventilator in an attic is a desirable feature. (See FIG. 9-7.) Because of trapped air, an attic area can reach 150° F on a hot summer day. A power ventilator that is thermostatically controlled greatly reduces the heat load on the building. Usually the thermostat is set to activate the fan in the ventilator when the attic temperature is about 100° F. A power ventilator provides two additional benefits regarding air conditioning. By reducing the heat load on the structure, less electrical energy is required for air-conditioning units. And for those homes with a central air-conditioning blower coil located in the attic, the unit operates more efficiently at lower surrounding temperatures.
Thermostatically controlled power ventilator mounted between the roof rafters.
The power vent should normally be operating during the warm days of summer. If it isn’t, either the unit is malfunctioning or the thermostat is improperly set. On many units the thermostat is exposed and can be manually adjusted. But if the thermostat is factory set and not accessible, the unit will require professional maintenance. On cool but not cold days, you can usually check the power vent, assuming the thermostat is exposed, by lowering the temperature control setting until the fan is activated.
Some structures have attic fans. Check the fan before you go into the attic. If the fan is turned on while you are in the attic, be careful when walking around. In some homes, the area of the vent openings for the attic fan is too small for the size of the fan; consequently, the air that is moved by the fan is partially blocked from leaving the structure. As a result, pressure is built up in the attic, which decreases the efficiency of the attic fan. If the fan is turned on before you go into the attic, put your hand over any electrical outlet box located on the level just below the attic. If you feel air rushing onto your hand, the attic vent openings are inadequate and should be increased. Some attic fans are controlled by manual snap switches. From a convenience point of view, this is not as desirable as a timer switch or a thermostat switch. If this is the case, consider its replacement.
Attic fans are mounted either in the attic floor or on the exterior sidewall of the attic. They have movable louvers that open when the fan is activated and remain closed when the fan is off. This operation creates a potential problem when the fan is located on the exterior sidewall. During the winter months and during portions of the summer months when the fan is not operating, the louvers will be in a closed position and will thereby completely close off the vent opening, causing the attic to be inadequately ventilated. This problem can be avoided by adjusting the louvers so that even when the fan is not operating, they remain in a partly open position.
Some houses have no access to the attic area. If such is the case in your home, the probability is very great that the area is inadequately insulated by current energy standards. The amount of ventilation in the area is also questionable. Installing an access hatch to the attic is recommended.