Tile Roof Applications
Inside this Article
Installing PV arrays on tile roofs is more time consuming, complicated and expensive than installing on asphalt shingle roofs. Yet, despite the added difficulty, tile-roof solar installations are growing dramatically in active solar markets like those of Hawaii, California and Arizona. High utility rates, robust incentive programs, a plentiful solar resource and rapidly dropping module prices have helped make solar on tile roofs a reality. Aiding this growing market, new PV array mounting systems for tile roofs and improved techniques are making installation faster, easier, more reliable and less expensive.
In this article, we examine the most common tile roof systems that installers are likely to encounter and address three array mounting and weatherproofing approaches developed specifically for tile roof applications. But first, a word of caution: Tile roof construction varies widely throughout the US, and some configurations make installing an array difficult or impossible without reroofing or using advanced mounting techniques. Be aware that solar installers cannot easily tackle applications like fully adhered tiles (hello, Florida and Hawaii), elevated underlayments, skip sheathing and other atypical tile configurations. In these situations, you would be wise to subcontract a capable roofing contractor to ensure reliable waterproof penetrations and the structural integrity of the array and affected portions of the roofing system.
Replacing Tile Roof Underlayment
Tile roofs installed by a skilled roofing contractor can last many decades because tile dissipates heat better than asphalt shingle roofs. In addition, this heat-dissipating capacity lowers air conditioning bills, which is why tile roofs have become the norm in the southwestern US over the last three decades.
While the tiles themselves can typically last 50–75 years, homeowners are often surprised to learn their roof underlayment may need replacing in as little as 15 years. This has major implications for PV installers. Most underlayments used on tile roofs are made from asphalt-impregnated felt paper. Unfortunately, felt paper decomposes at an undesirable rate when exposed to excessive heat, UV and moisture.
Replacing the tile roof underlayment beneath an installed PV array is a major undertaking, as it requires the removal of the PV modules, racking, wiring, mounts, roofing tiles and battens. The cost of removing and reinstalling a PV array on a tile roof typically ranges from $0.75 a watt to $1.25 a watt, plus the cost of any necessary roofing repair work. This equates to a whopping 20%–40% of the cost of a new PV system. Since the average tile roof needs to have the felt underlayment replaced every 15–25 years, homeowners should be strongly encouraged to replace the underlayment and battens beneath the array prior to the installation of a new PV system. The use of a high-quality underlayment ensures that the roofing system will last the 25-year life of the array.
Types of Roofing Tiles
Roofing tiles come in a dizzying array of materials, sizes, shapes and colors. Clay tiles are less common than concrete tiles, but many high-end homeowners opt for clay tiles to achieve that traditional old-world look. While clay tile roofs can be very attractive, they are usually more expensive to install. One-piece clay tiles are very strong, unlike the classic sand-cast Mediterranean-type two-piece tiles. Sand-cast clay tiles are brittle and crack when walked on. Array installations on roofs that use cast two-piece tiles are best approached with the strip-and-go method we describe later in this article. Concrete tiles are more common in residential roofing. A skilled roofer or solar installer can walk on them with minimal breakage.
Since breaking tiles is a reality, installers address this challenge by repairing dog-ear breaks with tile adhesive and relocating the repaired tiles in less visible areas under the array or elsewhere on the roof. Larger breaks require replacing the tile. Finding replacement tiles is not too difficult, but an exact color match is unlikely. Installers often remove original tiles from less visible areas of the roofing, replace them with off-color tiles, and use the original tiles in the visible areas around the array. If the color needs to be consistent over the whole roof, painting an off-color tile to match the other tiles might be the only option.
Roof tiles can be either flat or curved. Installing a PV array on flat, or low-profile, tiles tends to be a bit simpler than installations on curved tiles since the tile flashing used to seal roof penetrations does not need to be molded to the tile. However, unless the roof system has a vented eave riser, a flat-tile roof is not as well ventilated as a curved-tile roof. There are two types of curved tile: high-profile S tiles and medium-profile W tiles, also called villa tiles. Curved-tile roofs often require more time for array installation, especially if you use conventional standoffs and double flashing to secure the array to the roof structure.