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
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).
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
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
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
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.
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
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.
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.
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
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
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).