“Roof Leaks”

By Robert G. Wilkin, P.E., Associate

Roof Leaks is in quotations because many roof leaks are not the result of leaking roofs.  Many roof leaks are caused by mechanical equipment, punctures caused by mechanical equipment, repairs, or other reasons. 

After recently reviewing the roofing at several schools, which were less than 5 years old, for new photovoltaic installations, we discovered four of the roofs had roof leaks directly below the mechanical units.

Leaks can also occur around improperly sealed access doors and joints in the air handling units themselves or roof top duct joints.  I have seen water testing ducts once produce a leak 50’ away and 3 stories down.  Single ply membranes can easily be punctured by loose doors or fan covers blowing off.

Roofers often do a good job installing cone flashing or pitch pockets but we have seen electrical and gas lines flashed with ice and water membrane, duct tape or spray and a plastic bag that are less than adequate.

Leaks at the roof level can also be caused by masonry above the roof level where there is no (or deteriorated) through-wall flashing.  Several times I have encountered roofing installed with a surface applied termination bar on masonry with the roofing over the weep holes on top of a functioning through-wall flashing.  When roofing is installed in this way water collected by the flashing is directed directly under the roofing.

Roofs are typically forgotten until a leak occurs, and then the owner assumes it is the roof.  A proper analysis of the source of the leakage can be very beneficial rather than doing repairs by guess work.  Water and infrared testing can be useful tools when analyzing the source of the leak.  

Lesson learned:  I was once asked to design a third replacement roof on the terrace when it turned out that the window wall was the source of the leaks.  Be sure analyzing the source of the leak before wasting your money on unnecessary repairs!