Transitional Flashings Reduce Water Leaks
by Richard K. Olson, president & technical director, Tile Roofing Industry Alliance
(Editor’s Note: Richard K. Olson is president and technical director for the Tile Roofing Industry Alliance. The association represents industry professionals involved in the manufacturing and installation of concrete and clay tile roofs in the United States and Canada, and works with national, state, and local building officials to develop installation techniques, codes, and standards for better roofing systems. Olson can be reached at firstname.lastname@example.org.)
Today’s roof designs are more creative and utilizing a greater product offering for steep-slope applications. The integration of multiple roof slopes, transitional products, and exciting roof geometry can challenge the design professional for how to keep water out of the roofing assembly. The proper use of transitional flashings can reduce the opportunity for a leak. For steep-slope roofing, the priority is to keep the water on top of the roof cladding, or to daylight the water via proper flashings to the eave and off the roof.
We often see where valleys will terminate onto an adjacent roof section where only the valley metal is utilized. This will allow water from the valley to carry across the adjacent roof area and can breach the head lap of the roof cladding. The use of an additional transition flashing that can extend out over the first course of the downslope roof will reduce that leak potential. The transition flashing should be called out on your details to fit under the valley metal and transition on the top surface of the adjoining plane. For products such as concrete or clay tiles that can have barrel tile profiles, a malleable metal that can be made to simulate the profile will help reduce water entry and allow the metal to blend into the tile profile. Painting of the flashing to match the cladding color will further reduce the visibility. We often see this transition flashing left out, due to the building owner’s objection to the aesthetic issue, resulting in a callback for the contractor.
There is the increased use of multiple roofing materials on the same roof plane for either aesthetic or design considerations. This creates the need for the proper transition between materials. One of the more frequent applications we see in our tile industry is the change from tile to shingles under the solar panels to reduce the overall roof height of the solar panels. When this is considered, the design professional will need to call out the transitional flashing details on all sides of the panel to make sure the water is able to flow downslope properly. In many cases the installation of a side wall around the panel will allow a formal rake metal to be installed. This will keep the water on the two sides diverted downslope. The transition flashings for the upslope side can then direct the water onto the shingles and allow it to transition off the roof, or transition back onto the tile surface on the succeeding courses downslope.
Roof Slope Change
We are seeing an increase in the use of roof slope change, where a steep slope will transition onto a low-slope segment over the patio, carport, or family room. In these designs, the use of a transitional flashing that extends back up under the steep-slope portion will help reduce roof leaks. The flashing should carry out over the low slope and some form of weather blocking should be used to reduce water entry back up the steep-slope application. As a reminder, low-slope applications for tile require a sealed system under the tile. When steep-slope roof slope changes are required, the design professional will need to review and provide details for properly addressing flashing needs. There may be issues of interlocking capabilities, coursing, and compatibility for proper performance that will require additional weather blocking or flashing materials to provide proper performance, while not affecting aesthetic desires.
The most challenging area for designers is the proper flashings for roof penetrations. Chimneys, skylights, and accessories will need to be reviewed for properly keeping water from entering. The proper use of a step flashing or pan metal that will direct the water around the penetration and back onto the cladding surface will reduce leak potentials. For wider penetrations, the use of crickets will help redirect the water downslope. Where roof vents, pipe stacks, and electrical connections are encountered, there will be the need to ensure that both the top of the cladding and the hole in the sheathing are sealed. For tiles, both a deck and top flashing are needed to meet this requirement.
For any roof penetration, the design professional should review the anticipated tributary water that might be a factor. This may be from upslope or adjacent roof planes. Today’s multi-roof planes create additional water flow issues as large amounts of water from higher roof planes are transitioned via free flow or gutters to smaller roof planes below. The ability to flash or provide some form of weather blocking to reduce additional water entry might be considered.
With proper attention to transitional flashing needs, design professionals can achieve a long-lasting, aesthetic option to the building owner. The ability to keep water from breaching the roofing system is one of the keys to long-term performance.