Get to the bottom of roof leaks
“April showers bring May flowers,” or so goes the saying. Those showers may also bring roof leaks and attendant damage. Chances are that those leaks have less to do with the shingle roof that you can see and more to do with roof-flashing details that you may have never noticed. Flashing is the metal barrier that bridges the edge between the other roofing material and the structure of the home. When this detail is improperly installed, leaks are guaranteed, no matter how good the shingles.
All along the perimeter of the roof there are gaps between the roof decking and the fascia board that trims out the eaves and gables. Drip edge is an L-shaped band of metal flashing. One surface caps the roof decking and the other extends down against the fascia. Properly installed, drip edge closes the gap between decking and fascia, provides extra support for the shingles and protects the fascia from overflowing gutters. It also keeps critters from gnawing their way into your attic by expanding the slot at the roof edge. It’s a pretty safe bet, though, that drip edge is absent from your home. Although required by roofing manufacturer’s specs, it is commonly neglected in the installation
Roofs have peaks and valleys. When roof planes join to form a valley, additional protection is required to prevent leaks in this trough. Valley flashing is sized according to the roof slope—the lower the slope, the greater water accumulation; the greater the water accumulation, the wider the valley flashing; the wider the flashing, the better protection (unless the installer uses the same width flashing in every application or nails the flashing in place in a manner that puts nail holes within the protected area). Given the complexity of some roof designs, valleys are often forced to act as collectors, accommodating a water load for quite an extensive time. Overbuilding the flashing in such circumstances is good insurance against some hard-to-diagnose-and-locate roof leaks.
Head wall flashing
Head walls meet the roof along a line parallel to the ground. Continuous flashing is required to kill the joint between the wall sheathing and the roof. Angled flashing is nailed to the wall sheathing with its lower panel extending over the shingle roof. Siding is then installed on the head wall covering the top of the metal flashing. The siding itself becomes “counter flashing,” blocking water from entering above the edge of the metal flashing.
Sidewalls meet the roof along a line perpendicular to the ground. Whether lap sided or masonry, sidewalls require the most complex siding detail: step siding. Step siding is a compound angle piece of metal following the lines of both the sidewall and the roof. It is, effectively, a metal shingle. Step flashing units are installed along with the roofing shingles, each overlapping the previous unit – stepping up the roof – with the portion flat to the roof over one shingle and counter-flashed by the next.
The whole idea is to provide a continuous, impenetrable path to shed water off the roof. The problem is that often the homeowner encounters “make-do” flashing. Make-do flashing is quicker, easier and cheaper and, upon first glance, you can hardly tell any difference. Until it rains.
Tune in to The Bob and RodMan Home Show every Saturday from 9 to 11 a.m. on 920 AM-WGKA to learn how to improve your house or apartment. RodMan is a certified home inspector, knows residential property appraisal and is a hands-on home renovator. Bob owned a roofing company, has reclaimed distressed properties for years and has Master Licenses as a plumber, electrician and HVAC mechanic. www.bobandrodman.com