Inspecting the attic for proper ventilation is essential . Ventilation permits air to circulate through the attic. In the winter, it prevents warm, moist air from being trapped in the attic where condensation can cause damage. Ventilation keeps the roof deck cooler, lessening the possibility of ice dams. In the summer, ventilation prevents damaging heat and humidity from being trapped in the attic. Moisture can be trapped if the attic isn’t properly vented, causing the deterioration of the insulation and the wood framing. In addition, inadequate attic ventilation can damage the roof system. The movement of air prevents or inhibits moisture condensation on the under-surface of the shingles or shakes or on the roof decks.Two kinds of air movement help ventilate the roof. First, warm, moist air rises naturally in the attic and is exhausted out through the ridge vent. Second, wind passing over the ridge vent draws air and moisture out of the attic. Vents should be located in the soffits and the gable ends or, at the ridge lines. Gable vents are least effective and are located near the gables and does not cover the entire roof. Ridge vents are installed along the peak of the roof.
Should condensation occur in an improperly insulated or ventilated-attic, mildew and wood rot compromises the wood rafters and eventually the roof deck. As a home inspector, we need to determine that the attic contains enough insulation that is firmly placed between the ceiling joists or roof rafters. If this is the case, the inspector must verify that there is an air space between the insulation and the sheathing. If there is no air space, moisture condensation can decay the sheathing or roof rafters. The insulation should not be pushed up against the eaves because it blocks the airflow through the soffits into the attic space. To ensure this doesn’t happen, baffles made of polystyrene material are placed in the space between the insulation and the sheathing. We need to determine whether there is adequate flow of air both across the attic space and from the attic floor through the roof. The roof rafters are examined for warping, bowing, and signs of wood rot.
It’s also important to check the the bath fan connections in the attic. They have to terminate out the side of the house or the roof. Never terminate a bath fan into the attic. Water stains on the ceiling around your bath fan may indicate a leak coming from the vent cap on your roof, but condensation is the more likely culprit. If bath fan ducting isn’t properly insulated, the moist air from your house will condense inside the duct. The first step is to head to the attic. You may find that the insulation simply needs to be refastened. If you see that your duct isn’t insulated at all, pick up duct insulation at the home center. Use zip ties or aluminum tape to fasten the insulation. If your ducts are properly insulated, another potential cause of condensation is lack of use. Bath fans have a damper designed to keep the outside air from entering in through the fan, but that valve doesn’t stop warm air from escaping. Whether you use your bath fan or not, some warm air will still escape into the ducting. On very cold days, that warm air is likely to condense inside the ducting, especially if the fan is never run to dry it out. Guest baths are particularly prone to this problem.
The bottom line: Before you climb on the roof to look for leaks, make sure your bath fan duct is insulated, and run the fan more often and for longer periods. Switches with built-in timers are available. More here on moisture issues in the home: https://goo.gl/UXRJ8W
John Richter was an HVAC technician for 20 years and currently a home inspector with Premier Home Inspections.