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Tile roofs have been used for centuries, and with good reason. Tile roofs are strong, versatile, and durable. Available in a variety of styles and finishes, tile adds curb appeal to any home, be it American Colonial, Spanish Hacienda, or French Provincial. As with any roof type, weather proofing and installation are keys to long-term performance. This article will provide tips on how to avoid common errors in tile installation.
Building codes, including the Uniform Building Code (“UBC”), Building Officials and Code Administrators (“BOCA”), International Building Code (“IBC”), International Residential Code (“IRC”), and many local jurisdictions, provide prescriptive requirements for installation and flashing. Several industry standards have been developed and are used in order to assure quality installation of clay and concrete tiles, such as the National Roofing Contractors Association, the Roof Tile Institute, and the Western States Roofing Contractors Association. But even with these established standards, tile roofs are frequently installed incorrectly, with mistakes that are repeatedly the same.
The first issue to address is the proper protection of the roof decking and other building components through the application of a weather-resistive underlayment. Some local building codes may require two layers of underlayment be provided due to cold climate conditions or the low slope of a roof; therefore, it is important to verify underlayment requirements before installation begins. Underlayment is a crucial component to the roof because it acts as a drainage plane for a water-shedding tile roof. Tile roofs are unique in this aspect, as the primary drainage plane is the underlayment and not the top-most layer like other roofing materials, such as asphalt or wood shingles. This is why any puncture or tear in the underlayment should be sealed so no water intrusion below the underlayment can occur. Water intrusion could eventually result in leaks into the residence, which could cause a substantial amount of damage. However, leaks don’t always show up right away, even though deterioration could be occurring to the roof decking and other wood components.
It is also important to pay close attention to the direction and order of lapping the underlayment with flashing, especially at roof penetrations, eaves, and rakes. The underlayment should lap over the top of roof penetration flashings and under the bottom, creating a shingle-like order to ensure the water shedding capabilities of the underlayment. This technique is important at small penetrations, such as plumbing and roof vents, as well as at large penetrations such as skylights and chimneys. The flashing surrounding these large penetrations is made up of several pieces, so the same shingle-like lapping is essential at these locations. It should also be mentioned that at penetrations with a width larger than 30 inches, installment of a cricket flashing is recommended to prevent snow and debris buildup . At rakes, the underlayment should be lapped under the rake flashing to prevent water intrusion from wind-driven rain and snow below the underlayment. At eaves, the underlayment should be lapped over the eave flashing in order to provide a continuous avenue for water to drain off of the roof. In all of these cases, reverse-lapped underlayment and flashing interfaces can result in damaged components and can eventually lead to leaks.
Example of correct penetration installation for tile roofs.
Source: Concrete and Clay Roof Tile Installation Manual for Moderate Climate Regions Design Criteria, by Roof Tile Institute and Western States Roofing Contractors Association
One roof malfunction that can be easily avoided is the occurrence of ice damming. Two events are necessary to create an ice dam: a warm interior and a cold exterior. When snow accumulates on a roof with a warm attic, it begins to melt. When the melting snow reaches the end of the roof at the eaves, which stay cold as they are not adjacent to attic space, the melted snow refreezes. This situation can cause major damage to homes if the moisture management materials are not correctly lapped. If not properly protected, water can travel under the underlayment and enter the home’s walls, ceiling, and building components. This is just one more reason why paying particular attention to the lapping conditions of moisture management materials is so important.
However, even if a home’s moisture management materials are correctly installed, the occurrence of ice damming can still create additional weathering to these materials, resulting in a shortened life of the materials. Other precautions can be addressed to ensure that ice damming occurrences are significantly reduced. One option, and probably the most effective, is to eliminate the warm attic environment. To do this, insulation should be placed above the ceiling in the attic to keep the warm air in the living space of the home and not in the attic space. Additionally, sufficient ventilation should be established to provide a constant flow of air through the attic space from the ridge to the eaves. If this cold attic system is correctly installed, the probability of ice damming should be completely eliminated.
Example of ice damming at eaves.
Source: Lerch Bates
Example of ice damming at a rake-wall interface. Note how the kicker flashing is directing the water/ice away from the wall at this location.
Source: Lerch Bates
Particular attention is also needed when installing underlayment in valleys. Valleys are located at the intersection of two sloping roof planes which creates an area of concentrated water flow, so additional protection is necessary to prevent water intrusion. Whether using additional underlayment or sheet metal flashing at valleys, installation should consider the flow of water. This will ensure all valley components are lapped in a shingle-like manner, in the direction of water flow.
Example of tile roof valley. Note battens and bird stop extended into valley flashing resulting in debris accumulation. Construction debris, such as tile fragments and underlayment scraps also block the flow of water.
Source: Lerch Bates
Example of correct valley installation for tile roofs. Note placement of battens around valley flashing.
Source: Concrete and Clay Roof Tile Installation Manual for Moderate Climate Regions Design Criteria, by Roof Tile Institute and Western States Roofing Contractors Association.
Battens are another item that is occasionally overlooked or installed incorrectly. Battens are usually 1-inch x 2-inch wood supports nailed or stapled horizontally to the roof decking. Tiles with projecting anchor lugs are hung on the battens and fastened to them. The purpose of battens is to provide space for water and debris to drain below the tiles, as well as to allow the system to ventilate. In order to create a path for water and debris to exit the system, 1/2-inch openings should be provided every 48-inches in the battens. It is also pertinent that battens be withheld from the valleys so a clear drainage path is present for water and debris to exit the system. Another method for providing a drainage plane below the tiles is to install counter battens. Counter battens are nailed or stapled vertically to the roof decking and are used to support the horizontal battens. Battens should be spaced at a maximum of 24-inches apart on the counter battens, and are recommended to be spaced 16-inches apart at locations with high snow loads to avoid deflection of the battens, which could result in cracked or damaged tiles .
Example of correct batten installation.
Source: Concrete and Clay Roof Tile Installation Manual for Moderate Climate Regions Design Criteria, by Roof Tile Institute and Western States Roofing Contractors Association.
Fastener requirements for tile roofs can vary greatly from roof to roof, but some basic rules always apply. First, when installed directly on the deck, without battens, one fastener must be provided at every tile. If battens are being utilized, additional factors determine the fastening schedule. The pitch of the roof must be known when determining requirements. Because tiles with projecting anchor lugs hang on the battens, a low-slope roof has less stringent fastener requirements than a steeply sloped roof. If the slope of the roof is under a 5:12 pitch, fasteners are not required. On roofs with a slope between 5:12 and less than 12:12, one fastener is required per tile on every other row. For slopes 12:12 and greater, one fastener per tile is mandatory. Additionally, if the tiles being installed are less than 9 lb/ft2, then all tiles require one nail on any slope . High wind and snow areas have special fastener requirements depending on the governing code. If the wind speed exceeds 80 miles-per-hour, or the height of the structure exceeds 40-feet, all tiles are required to have one fastener, rake tiles are required to have two fasteners, wind clips are to be utilized at all eave tiles, and mastic is to be applied to the noses of all ridge, rake, and hip tiles. In snow areas, two fasteners per tile are necessary for all tiles.
Example of tile roof damage due to high winds and fewer than required fasteners.
Source: http://www.polyfoam.cc/images/CharleyMortar-Lg.jpg
