Most old homes don’t have just a single roof. Many have separate roofs over porches, additions, bays or towers. As a result, there are typically numerous intersections where roofs meet vertical surfaces. Chimneys, skylights and plumbing vents also interrupt roof surfaces. If the flashings at these joints and intersections aren’t installed correctly, and with proven methods, they leak. Leaks at these locations are much, much more common than in the field of the roof itself.
Unless a good quality slate or metal roof was installed and maintained, the roof covering on an old house was likely replaced at some point. Possibly, several roofs have been installed. When roofs get replaced, the flashings often don’t get reinstalled with the attention they deserve.
The most common flashing detail that rarely gets installed correctly is where the roof meets masonry walls or chimneys. It seems the skills of many “professional” roofing contractors, when it comes to flashings, is limited to liberally smearing tar (roof cement) hoping it won’t leak before the customer’s check clears.
Where the edge of a sloped roof meets vertical masonry, step flashings should be installed with each course of shingles, so that water runs down the steps and not into the joint. To keep water from running down the masonry wall behind the step flashing, a counter flashing should be installed. The top of the counter flashing needs to terminate in a secure, water tight seal. The most reliable method of terminating the counter flashing is called a reglet.
To create a reglet, a circular saw with a masonry blade is used to cut a kerf into the wall. The top of the metal counter flashing is then bent into a V shape and inserted into this groove. A thin bead of quality sealant (not tar) is then used to create a durable, long lasting seal. If executed properly, with quality materials, this method of flashing can last at least as long as the roof covering.