When locating a leak, remember that water can’t run uphill, so leaks on a pitched roof cannot be below where you see evidence of a leak. Water can enter through exposed nail holes or an area with missing shingles, traveling over old layers of roof and roofing felt until it reaches a gap or tear that allows it to penetrate to the roof deck. From there, it may run over the plywood until it crosses a joint – whereupon it may resume its journey along a rafter or the underside of the decking.
Finding the origin of a leak when the underside of your roof is hidden, such as with cathedral or vaulted ceilings, is a real challenge. Water can travel many feet from where it enters before showing itself. With drywall or paneling on the ceiling, it may travel even further. A small leak may not even be noticeable except during prolonged rain fall, but that doesn’t mean it’s harmless. Moisture inside the roof assembly can degrade insulation and promote the growth of mold and wood-rotting fungus.
With substantial leaks, you will see discoloration on your ceiling. On a horizontal ceiling, water may pool and saturate the drywall. If you see this happen, puncture the saturated area with a pencil and allow the water to drain into a large bucket until you can repair the roof. If the leak cannot be found by inspecting the roofing, a sizable section of drywall will have to be removed to pinpoint its location. Once the leak has been located, technicians will measure from reference points, such as a chimney and the ridge, so they can transfer the leak location to the roof.