A botched roofing job is almost always about installation. Manufacturers aren’t the only ones who think so; most roofing contractors would agree. If the product fails, it’s usually because of the way it was installed.
You don't have to look long or hard to find out what are the most common installation errors. A Google search of “roofing installation errors” produces more than 1.5 million results, many of which lead to roofing company websites. What could go wrong? That may depend to some extent on the roofing material. And since four out of five roofs in the U.S. are asphalt shingle, much of what’s online is focused on shingle installation mistakes.
GAF, which publishes a blog for pros on its website, recently listed the “5 Common Roofing Errors” its experts see on finished roofing jobs. If you’ve been called out to a roof that’s failing, especially a new roof that’s failing, there are no surprises here: installing shingles on flat roofs; failure to use drip edge, starter strip, and membrane flashing in vulnerable places (such as eaves, chimneys, and skylights); and, of course, nailing. “When an installer does not know the proper number of fasteners needed per shingle or their placement on the shingle, it can cause catastrophic problems,” blog author Erasmo Fuentes says, with some understatement.
Brad Caldwell, owner of Roof, Rinse & Run, a roofing and pressure-washing company in Auburn, Ala., cites all those and more on his company blog (other sins include lack of proper ventilation, and use of 3-tab shingles on hips and ridges). He publishes a photograph there of chimney flashing so laughably bad you’d have to believe the picture was staged. It wasn’t.
In a posting earlier this year, Zenith Roofing, of Fort Worth, Texas, offered its own list, which calls particular attention to valleys and flashing at pipe penetrations. In addition to clear instructions on where the problems areas are and how to avoid them during installation, the site sometimes offers an explanation for why installation errors occur. For example, when discussing why pipe penetrations are so frequently the cause of problems in a re-roof, the site says: “Errors occur because installers are paid to put shingles on and they race past pipes with little effort and don’t return to finish the flashing.” Enter water.
All Roofing Solutions, in Delaware, cites a common problem that others seem to have left out: re-use (instead of replacement) of existing metal flashing. “The old flashing may look serviceable,” writes the author of “Shingle Roofing Installation: Common Mistakes Made by Contractors,” but consider that there is always a possibility that it has been punctured or damaged. New flashing is a small component in the cost of a roof replacement. Always install new flashing.”
Up to now, all we’ve been talking about is shingle roofing, but other roofing types are not exempt from similar problems. Back in 2008-2009, slate roofing specialist Joseph Jenkins, who publishes Traditional Roofing Magazine to an audience of mostly slate aficionados, listed 21 contractor errors (PDF) in connection with slate roofing jobs. His labor of love leaves nothing out, from culling bad slate from the batch (“Poor quality slates can originate from any quarry”) to nail length, flashing, snow guards, correct tools, and so on.
And as metal roofing grows in popularity, especially among high-end homeowners, there are those online who are anxious to point out the mistakes that could make this roofing system—which positions itself as a permanent roofing solution—problematic. Denise Brown at eHow calls attention to some common "Metal Roofing Problems" you may never have heard of but should know about if you’re thinking of taking on metal roofing, which more and more shingle contractors are. These include improperly prepared roof sheathing (soft, moist, or spotted) and “failure to take the prevailing wind patterns into account … if wind has a chance to get under the metal roof, especially around the flashing, it can cause the roof to billow. Over time this can cause the roofing screws or nails to work loose.”