Homefix: A leaking roof

Q: During extremely heavy downpours I have a problem with a leak around the heating/cooling vent in my bedroom ceiling. Now I've noticed another wet spot about 3 feet away from the vent. Is this a roofing problem, or do I need an HVAC specialist?

A: Sometimes a metal duct will form condensation that will drip to the area below the duct, but I would not suspect this in a hot attic. Sweating ducts can be insulated to prevent condensation.

On the other hand, roofs will leak eventually. Finding the exact spot where a roof leaks is difficult for even a skilled worker, because the location where water enters the roof and the location of the stain do not always line up.

As rainwater seeps through the roof, it will flow down the underside of the decking or along the side of a rafter until the stream meets an obstruction where droplets form and fall to the attic floor. Examples of obstructions are roofing nails, splinters or seams on the roof decking and knotholes on the sides of the rafters. If the leak is significant, water that hits the ceiling of the room will flow toward the lowest part of the ceiling and form a small pool.

The added weight of ceiling lights, fans and duct registers cause the drywall on the ceiling to sag at these locations, and even though the sag may not be visible to you, the water will find the lowest area of the ceiling and a stain will form. If the stain continues to grow, I would recommend you make a small — about 1-inch — hole in the ceiling to allow the water to drain out rather than allow it to soak into and damage the surrounding drywall.

A small hole is much easier to repair than a large section of ceiling. In either case, the ceiling will have to be repainted once the repairs are complete.

If the attic area near the ceiling stain is accessible, have a repairman locate the entry point of the water through the roof. Insert a stiff wire — I use a piece of wire coat hanger — and push it up through the source of the leak and through the roof shingles so the damaged area can be easily located on top of the roof.

Once the source of the leak is found, the shingles in that area can be replaced or in some cases easily repaired.

Working on a roof should be left to the professionals who have the proper tools and safety equipment for working high off the ground and near high-voltage overhead wiring.

Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home-improvement questions at C. Dwight Barnett, Evansville Courier & Press, P.O. Box 286, Evansville, IN 47702, or e-mail him at d.Barnett@insightbb.com. Please include a SASE with your questions.