When a roof is prone to leak, improper flashing is almost always the culprit. In roofs, as in life, “the devil is in the details.” That “devil” lives and thrives in improperly installed roof flashing.
A roof’s largest area is also the simplest to install flawlessly. That wide expanse of uninterrupted shingles, tile, or rolled membranes is called the field. There are no walls to tie into, no pipes sticking through, and no corners to turn. Any time obstructions are present upon a roof, a roofer must install proper flashing.
The most common flashing areas are:
- PIPES – Any pipe that penetrates the roof’s surface requires flashing around it, which is called a boot. The boot wraps securely around the pipe above the roof and attaches to a flat sheet of metal or plastic. That sheet laces into the shingle course. Back in the day, we chose lead as our pipe boot material of choice due to its flexibility and longevity but pesky squirrels chewed it and the long-term environmental impact concerned us. The industry soon adopted squirrel proof pipe boots made of neoprene gaskets with metal bases because they hold up well in the Texas heat and pose no environmental danger.
- WALLS – Dormers, parapets, and gables all require flashing at the intersection points between the roof and the wall. This flashing is comprised of pieces of formed metal, which turns the corner from the horizontal or sloped roof plane to the vertical wall plane. On a sloped shingle roof, step flashing and counter flashing make up the most common system. Step flashing is a flat sheet of metal bent 90 degrees down the middle, forming two “legs”. One leg laces in between the shingles while the other leg presses flat up against the adjacent wall. Typically the siding is installed over the wall leg, making it the counter flashing. Where brick or stucco is present, a separate piece of metal is set into the wall and turned down to cover the step flashing leg that is turned up from the shingles.
- DRIP EDGE – This metal surrounds a roof’s perimeter just under the starter course. It is typically 1 ½” by 1 ½” and 10’-0” long and bent in a long “L” shape. It prevents water from dripping on fascia wood, which causes premature rot.
- VALLEYS – The valley is the meeting point of two roof planes at a building’s inside corner. You will notice it is the spot where lots of water runs off during a rain shower and where leaves and debris gather first and stay the longest. Since so much water runs down the valleys, it is good roofing practice to install flashing under these shingles. We favor a sheet material called ice and water shield because it waterproofs and adheres to the roof deck. It self seals around any nail that penetrates it, making it a great waterproofing membrane.
Some misguided contractors still use rolled metal flashing under valley shingles, which is a poor practice born out of the days before asphalt shingles. When wood shingles were the common steep sloped roof material, metal flashing in the valleys was necessary because wood can’t bend to span the change in slope. Many roofers got accustomed to installing metal valley flashing and continued the practice with asphalt shingle systems. The problem? Metal expands and contracts at a greater rate than asphalt, causing the nails holding it in place to work their way up through the asphalt shingles. Those nails poke holes in the roof at a critical junction. Many roofers still place metal under asphalt shingle roof systems out of habit or ignorance but, in any event, it is not a good practice.
- DEAD VALLEYS – Dead valleys lack meaningful slope. Water simply stands or trickles off very slowly because the slope is so close to level. When a steeply sloped WATER-SHEDDING roof system includes a dead valley, the materials and application must change to a WATERPROOFING system for that area. Dead valleys notoriously leak because the steep slope roofers who contract these jobs often do not understand how to handle the occasional low slope roofing application.
To best flash dead valley areas, we recommend two-ply modified bitumen roofing systems that tie into the steep sloped system. These systems use asphalt-based materials that perform similarly. We do not recommend metal for dead valleys, in most cases, for the same reason we do not recommend metal in valleys that do have a positive slope.
- VENTS, ANTENNAS, STRUCTURAL COLUMNS, ETC. – We treat all these fixtures like PIPE flashing. There are different shapes and sizes but the application concept is very similar.
For more information about our roofing services, contact us today!
How much does a poorly flashed roof cost you?
At a minimum, buckets strategically placed throughout your home during heavy rains and the aggravation of hefty repair bills.
Drip, drip, drip, drip, drip…