by Dwight Barnett
Scripps Howard News Service
Q: I've been reading your column in the Detroit News and now find myself in need of professional opinions on two problems I discovered in my attic recently. I live in a colonial home with an attic that measures 30-by-30 feet. The attic is over three bedrooms, closets and one bathroom. Three adults live in the house and use the bathroom shower each day. I have a truss style roof with no ridgepole.
The first problem was caused by the roofers who installed my ridge vent two years ago. When cutting the air slot in the roof peak for the ridge vent, they did not adjust their saw depth properly. They cut through the roof boards and into the rafters that support the roof boards and roof shingles.
Consequently, I have an inch-deep cut in each of my rafters. The cuts are about an inch and a half from the end of the rafter. The roofer looked at the damage and said that there is no problem because the cut was not on the load bearing side of the rafter. Is this true?
I also have significant moisture in my attic for the first time. Two years ago I replaced two layers of roof shingles with a new layer. Prior to that time I had no moisture in the attic. The attic was ventilated by two 15-by-24 inch gable vents and three standard roof vents (louvers).
In the summer I also used a power fan in the roof that was turned on by a thermostat to provide more ventilation for the attic. When I replaced the roof, I installed a ridge vent the length of the roof and three soffit vents on each side of the house. The soffit vents are 8-by16 inches. The louver vents on the roof have been removed.
Recently, I discovered a lot of moisture, mold and some rot on the roof boards. This was only on the north side of the attic and is worse near the eaves. These conditions do not exist on the north side in the attic areas in line with the soffit vents.
I vent my bathroom fan to the outside through a roof vent. The exhaust venting is tight on the fan outlet hole and secured well to the roof vent. I have about 10 inches of fiberglass insulation in the attic. The first two inches are fiberglass batting, paper side down. The rest of the insulation is blown fiberglass. The insulation does not block the airflow from the soffit vents.
To correct the problem, the roof contractor recommends closing off the gable vents and adding four new soffit vents on each side of the roof. He believes the gable vents interfere with the soffit-ridge vent system. What do you recommend?
A: The roofer is right on both questions. First the load-bearing portion of a rafter is the face cut near the ridge and at the "birds mouth" cut where the rafter sits on the exterior bearing wall. Gravity forces push down on the entire length of the topside of the rafter and the force of the gravity is transferred to the bottom portion of the face cut.
What all this means is that as this rafter wants to sag the cut will close. If you have any concerns, have the roofer install a wood shim in each cut so that it cannot close.
The roofer is also right about the venting. Outside air enters the soffit vents and migrates up to the ridge vent where the warm moist air is released. The gable vents reduce the pressures inside the attic area by allowing air to flow away from the ridge vent. This creates pockets of dead air flow which you are seeing as moisture stains and rot.
In my opinion the entire soffit area should be vented and the gable vents covered on the inside to prevent moisture accumulation. You also need to add to the insulation in the attic. Two inches of fiberglass batt has an approximated rating of R-6 while the eight inches of loose fiberglass has a rating of R-17 to 18. The total is a rating of R-23 to 24.
In your area you need insulation that has a rating of R-30 or greater. If you insulate the attic yourself, use unfaced fiberglass batts and lay them perpendicular to the ceiling joists to cover all the areas of the attic floor.
(C. Dwight Barnett is a master inspector certified by the American Society of Home Inspectors. Questions may be addressed to him at P.O. Box 14091, Evansville, IN 47728, or e-mail dbarnett@evansville.net.)
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