Reducing Roof Leaks With Proper Flashing Designs
by Richard K. Olson, president & technical director, Tile Roofing Institute
(Editor’s Note: Richard K. Olson is president and technical director for the Tile Roofing Institute. 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.)
Winter rains have arrived in many parts of the West, and they bring with them an increased demand for repair and maintenance needs on steep-slope applications as roof leaks surface. The majority of these leaks will center on the lack of proper flashing performance, either from blockage or improper redirecting of water flow being allowed. This will provide an opportunity for the roofing professional to go beyond the immediate leak and help the building owner properly identify and upgrade the flashing systems.
The function of a flashing is to help properly direct the upslope tributary water onto the roof cladding or to daylight off the roof via pan or valley flashings. One might start with the evaluation of the overall roof design to determine the natural flow of water during weather events. Today’s complex roof designs will often allow water from multiple roof slopes to intersect onto adjacent roof areas. The ability to create valleys and roof-to-wall flashings that will properly account for the increase water flows is important. In some cases, there are complex roof designs that will not properly redirect water downslope allowing for accumulations or back-up of water on the roof cladding that can breach the cladding systems. It is important to not only evaluate each roof plane, but to establish best practices for how the total accumulation of water will affect the drainage needs. Gutters, valleys, and rake treatments can help reduce the flow area.
Roof penetrations continue to be the number one source of roof leaks. Over time the flexible flashings, mastics, and caulking can wear due to the differential of expansion and contraction of the metals allowing water to enter the roof assemblies. These should be evaluated to determine if the appropriate installation recommendations were followed for proper product performance. The use of mastics and caulking for plumbing and vent stacks should be in conjunction with a proper flashing component and not used as the only method of sealing. Concrete and clay roof tiles require the use of a base flashing at the deck and then a top flashing above the tile to ensure that water is not allowed to breach the system. When caulking and mastics are used, they should be selected based upon the manufacturers’ recommendations for the use and should be compatible with the materials. There are too many repairs where failures in relatively short times have occurred from improper material selection for specific roof applications. This is an area where roofing professionals can work with the building owner to upgrade the current flashings to be more design friendly and efficient.
Valleys are an important transition point for water flow and need proper maintenance to keep them clear of obstructions. In areas with trees or vegetation, there needs to be ongoing routine maintenance to remove foliage, dirt, debris, or any other foreign materials. If they are allowed to restrict flow, the lateral movement of water can find pathways under the roof claddings. For roof claddings where battens are utilized, they should not impede water flow in valleys or pans. The use of batten extenders that allow water flow should be used. When performing cleaning, roofing contractors should inspect the valleys for any aggressive wear, fastener holes, poor overlaps, or lack of proper adherence where sealed underlayment systems are in place. Reviewing the manufacturers installation or industry recommendations will help identify the proper requirements for the full roof assembly performance. Where valleys terminate onto roof areas, there should be some form of transitional flashings or skirts that will prevent the water from backing up under the valley. These transitional flashings can form to the cladding profile and be painted to match the roof color.
Roof-to-wall flashings prevent water from contact to the wall claddings, directing the water downslope. The height of the cladding above the pan flashing should be checked to prevent water wicking or excess moisture occurring. The roof-to-wall flashing will need to allow the water to flow off the roof via the pan flashing or to transition back onto the roof cladding surface if the wall transition terminates short of the eave areas. At the bottom of the pan flashing where a wall extends, the use of a kickout to direct the water away from the wall should be considered.
The proper flashing at eave areas requires attention to a couple of specific needs. Where gutters are present, there needs to be eave flashings that will transition the water into the gutter, not behind. The use of drip flashings with a turn out can prevent the water from flowing down wall systems where gutters are not being used. For raised fascias, the use of anti-ponding metals will help reduce any water from pooling upslope.
Crickets are special flashings designed to help direct water from behind larger openings such as chimneys, skylights, or roof-mounted accessories. The proper selection of cricket width, upslope length, and height will need to be reviewed for compliance with the local building codes and manufacturers’ installation requirements. The transition around a chimney or skylight will need to include the roof-to-wall flashing to fully encase the penetration. For concrete and clay tiles, this can be either with step or pan flashing options.
There are best practices and installation recommendations that can assist the roofing professional in identifying where flashing issues might be present. The ability to properly correct or upgrade the existing flashings will help extend the life cycle of any roof assembly.