Troubleshooting Roof Leaks

The cost of installing the roof on a new building usually amounts to less than 5% of the total construction cost.  Yet some lawyers estimate that 60% to 80% of construction lawsuits involve roof failures.  Often, it's a small leak that quickly grows into a big expensive problem.

The following problems are among the most common that have been encountered.  In every case, the leak could have been avoided had the installer used common sense and paid more attention to detail.

Asphalt Shingle Roofs

Problem:  No drip edge. If asphalt shingles are installed without a drip edge, it's only a matter of time before the plywood sheathing and fascia begins to rot.  Water dripping off the edges of the roofing is drawn by capillary action to the exposed edges of the plywood sheathing.
Solution: Install a metal drip edge at rakes and eaves.  The main purpose of a metal drip edge is to interrupt the wicking of water to the sheathing edges.

Problem:  Felt underlayment incorrectly lapped under (instead of over) the metal drip edge.  Any water that may get under the shingles - for instance, from wind-driven rain - should be carried by the felt underlayment over the top of the drip edge.
Solution:  Lap the felt underlayment over the drip edge.

Problem:  Valley shingles were not tabbed or spotted with roofing cement.  The large volume of water that collects in a valley can back up under uncemented shingles.
Solution:  In a closed valley, embed valley shingles in roofing cement.  Always clip the top corner of the valley shingles at a 45-degree angle.  This prevents debris from getting caught in the shingles and accumulating in the valley, and it also will direct water toward the valley centerline.  For extra protection, install a self-adhering eaves membrane under valleys.

Problem:  Roofing nails.  Exposed roofing nails are sometimes a source of leaks.
Solution:  Cover exposed nail heads with a dab of roofing cement when exposed nails can't be avoided (as with cap shingles).

Problem:  Excessive shingle overhang.  An installer apparently believed that increasing the overhang on the first course of shingles would help direct the water into the gutter, and would substitute for the metal drip edge.  However, the shingles eventually crease under their own weight and break off, exposing the edge of the sheathing beneath.
Solution: Shingles should overhang beyond the metal drip 1/8 nch to 1/4 inch, according to recommendations from the Asphalt Roof Manufacturers Association.