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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.

Colorfastness. The color of a clay tile is not affected by exposure to the elements; the same cannot be said of concrete tiles. Although most concrete roof tiles are manufactured with an integral pigment that colors the entire thickness of the tile, the color of concrete tiles will fade over time. "Concrete tile will never hold its color as well as clay," says Ken McGee, owner of The Tile Man, a supplier and installer of concrete and clay roof tiles in Louisburg, N.C.

Durability. Well-made concrete tiles should last a long time, although probably not as long as clay tiles; estimates range from 30 to 50 years. By contrast, many European clay tile roofs are still waterproof after a century of service. Traditional fired clay, although relatively easy to break, does not degrade from exposure to the elements. Because objects made from fired clay can't burn or rot, they are among the most durable objects known to archeology. Clay objects can easily last for thousands of years.

Although some early concrete roof tiles had durability problems, especially in areas with frequent freeze/thaw cycles, most concrete roofing tile manufacturers claim that today's concrete tiles are more consistent and durable than ever. Although there are reports of isolated cases of seriously deteriorated concrete roof tiles, tile manufacturers claim that such problems are rare and occur only when a bad batch of tiles gets through their quality-control systems.

"A few years ago, I saw a job up in the mountains where the concrete tile just disintegrated in the winter," says McGee. "It just fell apart. But that was unusual. Most of the manufacturers are very careful. I wouldn't let anyone knock concrete too much. You don't have to worry about concrete tile falling apart any more."

— Martin Holladay

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.

Tile Types

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).

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Figure 1. Each plumbing vent receives two layers of metal flashing. The primary flashing is galvanized and is installed at the same time as the asphalt felt (left). The secondary flashing is installed later, when the tiles go on. An S-tile roof gets secondary flashings made of aluminum, which is flexible enough to conform to the curve of the tiles (right).

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.

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Figure 2. Typically, hip boards — nailers that support the hip shingles — are 2x4s or 2x6s (left). Hip and ridge boards are installed after the roof has been felted and are later separately wrapped with felt (right).