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Roofing With Concrete Tile - Continued

Flashing. On most of our jobs, a sheet-metal subcontractor installs the flashing. We generally use 26-gauge galvanized steel flashing, unless the customer is willing to pay for an upgrade to prepainted galvanized steel or copper. The eaves generally receive a drip edge made from 2 1/2-inch-wide metal, which is installed under the asphalt felt. Our "W" valley flashing is 24 inches wide and is installed with clips, not nailed directly through the metal.

The sides of chimneys, dormers, and skylight curbs receive pan flashing, a rigid sidewall flashing that comes in 10-foot lengths. At the lower corners of the dormer or chimney, the pan flashing terminates onto a piece of aluminum or lead flashing, which conducts the water onto the top of a course of tiles below the roof penetration (Figure 3).

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Figure 3. The sides of dormers, skylights, and chimneys are flashed with galvanized pan flashing, which terminates on a piece of flexible aluminum. The aluminum flashing conducts the water onto the top of a course of tiles below the roof penetration.

Laying Out the Courses

We adjust the exposure of the tiles as necessary to achieve equal courses from the eaves to the ridge, maintaining a minimum 3-inch lap. Because the tiles we commonly use are 17 inches long, our maximum course height is 14 inches.

On asphalt shingle roofs, chalk lines are rarely necessary. With concrete tiles, on the other hand, every course needs a chalk line. These chalk lines correspond to the top of the tile courses and are snapped on the felt before the roof is loaded. On most jobs (especially on hipped roofs, which have no rakes), it's also helpful to snap at least one vertical chalk line, from eaves to ridge, to help keep the tiles aligned vertically.

Loading the roof. Once the chalk lines are snapped, we load the tiles onto the roof, using either a forklift or a “reach machine.” To avoid

heavy point loads that might stress the roof framing or sheathing, we distribute the tiles around the roof in piles of approximately ten tiles each.

Installing the Tiles

Before any S-tiles are installed, we install birdstop metal along the eaves. Birdstop metal has an L-shaped profile and comes in 10-foot lengths. One leg of the ell is nailed to the roof deck, on top of the felt and drip edge, and the other leg sticks up at a 90-degree angle. The upward-pointing leg has a wavy edge, conforming to the roof tiles.

Birdstop metal is designed to close the openings underneath the S-tiles while raising the end of the tile to the angle that matches the angle of the subsequent tile courses (Figure 4). The underside of an S-tile includes two parallel ridges designed to lock into the birdstop metal.

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Figure 4. Birdstop metal is the flashing that raises the heel of the first course of tiles while closing the openings below it (left). The underside of an S-tile has two ridges designed to conform to the birdstop metal (right).

When installing flat tiles, we use an eaves riser instead of birdstop metal. An eaves riser has a straight edge, instead of a wavy edge, to match the flat tiles. Some roofers elevate the first course of tile with a raised fascia board rather than an eaves riser. The problem with a raised fascia is that unless the installation is carefully detailed with felt and fiberboard or anti-ponding foam (a wedge-shaped piece of foam to direct water over the fascia), water that leaks through the tiles can cause the fascia to rot. Using an eaves riser or birdstop metal is simpler and eliminates the need for anti-ponding foam.

Laying out the tiles. After the birdstop metal is installed, the first course of tiles is laid out and nailed off. On subsequent courses, the top of each tile is aligned with a chalk line. With S-tiles, unlike flat tiles, the second course of tiles is not offset a half-tile width from the first course. S-tiles line up vertically like squares on a chessboard, rather than being staggered like courses of brick.

Concrete S-tiles must be laid out from left to right, as you're looking down on the tiles (with your back to the ridge), in order for the lap joints to engage. We generally lay out an entire course, from rake to rake, before nailing any tiles. We always eyeball the courses vertically, to be sure they line up. As long as they haven't been nailed, poorly aligned tiles can be adjusted by tapping them with a hatchet.

Nailing

Each concrete S-tile has been factory-punched for two nails: One nail hole is located in the pan (trough) of the S-curve, the other hole at the top of the curve.

Tile nails must be long enough to penetrate the sheathing by at least 3/4 inch. Usually, each standard field tile gets a single 2 1/2-inch-long (8d) galvanized nail, installed in the preferred nailing hole — the hole closest to the deck (Figure 5). As much as possible, we try to avoid penetrating any metal flashing with a nail.

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Figure 5. Each S-tile receives a single nail in the lower nail hole (inset). The upper nail hole is used to secure a cut tile that can't be nailed in the preferred hole. The most efficient way to install tiles is with a nail gun (left).

Once a course of tiles has been laid out and aligned, we nail the entire course of tiles with a pneumatic nail gun. If the nail gun is properly adjusted, nailing depth is consistent, and we have no problems with cracked tiles from overdriven nails.

A tile's second nail hole (the one at the top of the S-curve) is used only when the preferred nailing hole falls over flashing that shouldn't be penetrated or when a cut tile is being nailed. We keep a few loose 5 1/2-inch-long nails handy for use in these high nail holes.

Tiles that have been cut and are too small to nail — for example, the small triangular tiles abutting valleys — are secured with a dab of asphalt roofing cement. New formulations of tile adhesive are available, but they are more expensive than asphalt roofing cement. The main use of these specialized tile adhesives is in coastal regions subject to very high winds (see "Roof Tile Fasteners for High-Wind Regions," 5/96).