The location of stains showing water damage on the inside of the home can help reveal the problem area on the roof surface. This will make finding the point of entry easier and then enable one to make repairs in less time.
Stains at ceiling to wall joints on an outside wall can indicate water getting in through the overhanging eaves of the house. Water and especially blowing rain can penetrate these areas for several reasons:
Water seeing in under the bottom edge of the roofing material will eventually cause the wood in this area to rot. Gutters may hide this damage and even contribute to it if they are not cleaned regularly. Water intrusion at this point can cause the decking material and surrounding wood to rot.
Water then can penetrate to the interior ceiling and wall. Plumbing vent stacks placed within these outer walls and extending up through the roof surface can also be the cause of a leak in this area. The lead or neoprene flashings used to seal these vent stacks could have been damaged or not sealed properly.
Tree trunks and branches resting against the roof can cause these areas to retain moisture contributing to wood rot, as well as directly damage the roof by having constant contact with it.
If no apparent damage is found in this area of the roof, the leak could have been originating from other penetrations directly up the roof line from this area. The point of entry could be other plumbing vent stacks, exhaust vents, attic vents, etc.
Everywhere there is drainage for water inside the home, there will be a vent pipe attached to that drain line and vented through the roof. This fresh air is necessary for the water to drain properly. If water stains are evident on ceilings or walls in a bathroom, laundry room or kitchen, it could mean the leak is originating at one of the vent stacks.
If a single venting pipe is coming from the drain line and runs through the roof it is usually 1-1 / 2 "or 2" in diameter. If the pipe coming through the roof is 3 ", it probably means more than one vent line has been combined and then extended to the outside.
Building codes require bathrooms to have either a window which opens, or a mechanical exhaust fan installed to reduce moisture in the room. The exhaust duct for this fan is either rigid or flexible and will exit to the outside through the roof deck or an exterior wall.
The bathroom exhaust, like the plumbing vent stack, does not need to run straight up from the source through the roof deck. They may however be located in the general vicinity. Therefore, a stain on a bathroom ceiling could very well be caused by a leak at the exhaust vent for that bathroom. Exterior vents for bathroom fans are usually 4 "across on each side and square or rectangular in shape.
The clothes dryer also has an exhaust which will vent either through the roof or an exterior wall. If it penetrates the roof deck and there is staining on the ceiling in the laundry room, the source of the leak could be from this external vent.
The range above the stove top in the kitchen will usually have either an internal filtering system or it will also vent through the roof surface. Stains on the ceiling in this area could mean the leak source origin at this eternal vent. The duct from this exhaust fan is rigid and will run almost straight up through the roof.
On the roof this vent is usually larger than the bathroom exhaust vent caps. A range vent will terminate into a square vent on the roof which usually measures 10 "across on each side.
As you can see, the location of stains on the inside of the home indicating a roof leak gives clues as to the point of entry on the roof. Knowledge of plumbing and ventilating systems in the home and the ways in which these are exhausted to the outdoors, also give helpful information toward isolating the point of entry of a roof leak.
Mike N Beeghly