Roofing With Concrete Tiles

Felt underlayment and metal flashing are keys to a leak-free concrete tile roof.

By Fred Martin
Winter 2002

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, but in the past few decades concrete roofing tiles have become much more popular in large part because they cost about half as much as clay roofs. Here are tips for working with concrete roof tiles.

Tile Types

Concrete roof tiles are available in three basic design 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 or slate shingles.

Tile manufacturers provide special tiles for roof edges, ridges, and hips that match 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 finish the ridges, hips, and rakes (roof edges) with a simple barrel-shaped 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.

Wooden battens? Concrete roof tiles can be either installed on wooden battens running across the roof or nailed directly to the felt-paper covered roof sheathing. Here in San Diego, we have had excellent success nailing concrete tiles directly to the sheathing. Most tile manufacturers permit direct nailing, except on roofs with a pitch steeper than 7/12 or in very cold climates that might be subject to ice buildup.

When battens are used, they are typically 1-inch thick by 2-inch wide strips, with one course of battens installed 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.

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.

Preparation

Forty-pound felt paper. Roof tiles are not completely waterproof, so they require installing asphalt felt paper onto the sheathing under the tiles. Felt paper is the most important waterproof layer on a tile roof.

Tile manufacturers require, at a minimum, a single layer of #30 asphalt felt paper. 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 so that the sheets overlap each other at least two inches to shed water. The ends of adjacent sheets should overlap by at least six inches.

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 boards installed along ridges and hips that you nail the tiles into. These wooden nailers are made from framing lumber cut to the necessary dimension and installed on edge. The height of these nailers varies, depending on the desing of the tiles being installed. The most common size nailers used are 2x3s, 2x4s, and 2x6s (Figure 2). The ridge and hip boards are usually nailed in place after the roof has been covered with felt paper and then are individually wrapped with additional pieces of felt paper.

Laying Out the Courses

We adjust the layout of the tiles so we will end up with equally-sized tiles in each course of the roof. Then we snap chalk lines for every course where the top of each course will go. We do this before we load the roof with tiles. On most jobs it’s also helpful to snap at least one vertical chalk line, from eaves to ridge, to use as a reference during installation.

Loading the roof. Once we’ve snapped the chalk lines, we load the tiles onto the roof using either a forklift or a “reach machine.” We spread the tiles out in small piles to distribute the weight – each pile has no more than 10 tiles in it.

Installing the Tiles

Before we install any S-tiles, we install specially designed metal pieces along the bottom edge of the roof. These pieces enclose the openings at the ends of the S-tiles, and raise the first row of tiles to the right angle to receive the next course of tiles above it. (Figure 4).

When installing flat tiles, we also install a special piece of metal called an “eaves riser” . Eaves risers have straight edges that match the flat tiles. Some roofers elevate the first course of tile with a raised wooden fascia board rather than a metal eaves riser. Be careful to protect the wood from moisture problems if you do this.

Laying out the tiles. After installing the metal edge pieces, you can lay out and nail the first course of tiles. On subsequent courses as you work your way up the roof, the top of each tile is aligned with the chalk line for that course. We usually lay out an entire course across the roof before nailing any of the tiles in that course.

Nailing. Cement roof tiles each have two factory-punched nail holes in them. On S-tiles one nail hole is located in the “pan” (or low point) of the S-curve, the other hole is located at the top (or high point) of the curve. Tile nails must be long enough to penetrate into the roof sheathing by at least 3/4 inches. Usually, each standard field tile gets a single 2 1/2-inch-long (8d) galvanized nail (Figure 5). Try to avoid nailing through any metal flashings when you install tiles.

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 overdriving nails. A tile’s second nail hole (the one at the top of the S-curve) is used only when the preferred nailing hole (lower hole on S-tiles) 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 higher 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.

Cutting Tiles

Concrete tiles are best cut with a diamond blade, using either an electric circular saw or a gasoline-powered cut-off saw (Figure 6). If only a small corner needs to be trimmed and the cut area will be covered with flashing or a trim tile, it is often easier to knock off the corner with a hatchet than to cut it with a saw.

The concrete dust from the saw should be removed from the roof with a leaf blower (Figure 7). Otherwise, the dust will mix with moisture and form a hardened concrete paste that discolors the roof.

Valleys. The fastest way to complete a valley is to install all the largest cut tiles, and wait to install the small triangular pieces closest to the valley. Once all the full-sized courses along the valley have been installed, we go back and insert the small triangular pieces with a dab of roofing cement (Figure 8).

Rakes. Rake details along the roof edges differ, depending on the design of the tiles you install. The edges of the S-tiles we use are finished with a simple barrel trim tile. We secure each rake tile with two horizontal nails driven into the rake roof trim board (Figure 9). Flat tiles also come with special rake trim pieces too.

Hips and ridges. Once all of the field tiles are installed, it’s time to trim the hips and ridges. Each ridge tile is installed with a single nail into the ridge board. On the top of the nailed end of each ridge shingle, we lay down a bead of asphalt roofing cement to secure the un-nailed end of the next ridge tile.

The last step is to install mortar to fill the gaps between the top course of field tiles and the ridge and hip tiles. We use a simple mortar mix – 1 part Portland cement to 3 parts sand.

Walking on Concrete Tiles

It isn’t hard to break concrete roof tiles when you walk on them, so be careful. The best spot to place your foot is where the bottom of one tile is supported by the top of the tile on the course below. With S-tiles, it’s also best to place your foot so it spans the tops of two tiles. Plan your installation so you leave a path of unfinished roof to walk on until the very end of the job. That will make it easier to get from your ladders to the work areas without damaging finished tiles.

Fred Martin is the owner of Martin Roofing, a 53-year-old roofing company in San Diego, Calif., and is a past president of the San Diego Roofing Contractors Association.