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Our roofing company is located in Southern California, where most houses are roofed with concrete tiles. Until 30 or 40 years ago, almost all roof tiles installed in the United States were clay tiles, like those used for thousands of years in Europe and China. In the past few decades, though, concrete roofing tiles have edged out clay on residential roofs and now dominate the market.
Roof tiles, whether concrete or clay, are very resistant to fire. Although some traditionalists prefer clay tiles over concrete, there is no arguing with the main advantage of concrete tiles: They cost about half as much as clay (see "Concrete Tile vs. Clay Tiles," below).
Concrete Tile vs. Clay Tile
The main advantage of concrete tiles over clay tiles is their lower cost.
Proponents of clay tiles usually mention two advantages of clay over concrete
tiles: better colorfastness and longer physical durability.
Consider the Weight
Standard-weight concrete roof tiles generally weigh between 9 1/2 and 12 pounds per square foot significantly more than asphalt shingles, which weigh only 2 1/2 to 4 pounds per square foot. For houses where weight is a concern, many tile manufacturers offer lightweight roof tiles weighing 5 1/2 to 7 pounds per square foot. These tiles are made with a lightweight aggregate, like expanded shale, instead of sand.
If you're reroofing a house with existing asphalt shingles and you're not sure whether the roof structure is adequate to support concrete tiles, you should have the roof framing checked by an engineer before proceeding.
Concrete roof tiles are available in three basic profiles: mission S-tiles (or "Spanish S"), villa tiles (low-profile tiles with a double-S shape), and flat tiles, which are often designed to look like wood shakes or slates.
The job shown in this article used 17-inch-long Spanish S-tiles made by Eagle Roofing Products (see "Sources of Supply," page 4 of article). These S-tiles lock together along the sides, where they form a lap joint.
Tile manufacturers provide trim tiles specifically designed to complement their various tile profiles. Most roofs will require at least two different types of tile: standard field tiles and ridge tiles. For jobs using S-tiles, we trim the ridges, hips, and rakes with a simple barrel trim tile. Some styles of roof tile use a rake trim tile that differs from the ridge tiles. Some manufacturers also offer a "hip starter" tile, a trim tile designed to be installed as the bottom tile on a hip.
Low-slope installations. In general, the minimum slope for a tile roof is 3/12. If a customer insists on installing roof tiles on a roof with a pitch below 3/12, consult the tile manufacturer for installation specifications. Low-slope applications will require a carefully detailed waterproof membrane (for example, a self-sticking bituminous membrane) under the tiles. In addition, many tile manufacturers require that tiles on a low-slope roof be installed using a method that minimizes the number of fasteners that penetrate the membrane.
With or without battens? Concrete roof tiles can be either installed on battens parallel to the eaves or direct nailed to the felt-covered plywood or OSB sheathing. Here in San Diego, we have had excellent success direct nailing concrete roof tiles.
Most tile manufacturers permit direct nailing, except on roofs with a pitch steeper than 7/12 or in very cold climates subject to ice dams.
When battens are used, they are typically 1x2s, with one course of battens for each course of tiles. It's important to leave a gap of about an inch between the ends of adjacent battens, in order to allow a gap for water to drain. Battens should be no longer than 48 inches, for the same reason.
Necessary tools. The three most important tools for installing concrete roof tiles are a nail gun, a gas-powered cut-off saw or circular saw with a diamond blade, and a leaf blower for cleaning off the dust.
Prepping the Job
Roof tiles are not completely waterproof; in a driving rain, some water is likely to get past them. We install the asphalt felt carefully, because it is the most important waterproof layer on a tile roof.
Forty-pound felt. Tile manufacturers require, at a minimum, a single layer of #30 asphalt felt. Because a heavier felt is more durable and holds up better to foot traffic during tile installation, we always use #40 asphalt felt. The felt should be installed with a minimum 2-inch head lap and 6-inch side lap.
To avoid leaks at the sides of dormers, chimneys, and skylights, we carefully crease the felt and turn it up, rather than cutting it on the sheathing. For extra protection, we often use a peel-and-stick flashing membrane at penetrations such as roof vents, or at tricky areas around chimneys and skylights.
On tile roofs, all plumbing vent pipes get two layers of flashing. The primary flashing, a galvanized steel boot with a minimum skirt width of 6 inches, is installed at the same time as the asphalt felt. This flashing is bedded in asphalt roofing cement and is installed on top of one course of the asphalt felt, while the next felt course laps over the flashing (see Figure 1).
While workers are on the roof, it's possible to get a few unintended holes or
rips in the felt. Because the felt, rather than the tiles, is the roof's waterproof
layer, we're always careful to patch all such tears and holes with felt, roofing
cement, or a high-quality caulk.
Ridge boards and hip boards. Concrete tile roofs require special nailers at ridges and hips. These nailers ridge boards and hip boards are lengths of 2-by lumber, installed on edge. The height of these nailers varies, depending on the configuration of the tiles being installed. The most common sizes used are 2x3s, 2x4s, and 2x6s (Figure 2). The ridge and hip boards are usually toe-nailed in place after the roof is felted and then individually wrapped with additional pieces of felt.
by Fred Martin
This article has been provided by www.jlconline.com. JLC-Online is produced by the editors and publishers of The Journal of Light Construction, a monthly magazine serving residential and light-commercial builders, remodelers, designers, and other trade professionals.
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