Estimating Clay and Concrete Tile
- Field tile is usually sold in full pallets, and accessories in full boxes. Consult the manufacturer’s information for the number of field tiles per square, the number of squares per pallet, and the number of tile accessories packaged per box.
- It takes about 90 concrete field tiles to cover a square of roof area when using a 3-in. top lap.
- Add 3% to field tile quantities for waste and breakage.
Sheathing and Underlayment
Sheathing Options for Tile
A tile roof can be installed either over a solid sheathing or spaced sheathing.
Underlayment Options for Tile
- For slopes 4:12 and over, solid sheathing and 30-lb. felt will do. See Underlayment for Tile Roofs, below.
- On solid sheathing, 1x2 battens are mounted to the roof deck over the underlayment and between the roof eaves and the ridge. Battens are required on roofs with slopes in excess of 7:12, and are generally recommended on all tile installations. See Underlayment and Batten Layout, below, for underlayment application over solid sheathing.
Figure: Underlayment for Tile Roofs
| Roof Slope | Use Conditions | Underlayment (based on standard size tile with 3" min. overlap) |
|---|---|---|
| More than 20:12 slope | Normal Conditions | One layer of 30# asphalt-saturated felt (min.) |
| Heavier/Thicker tile application | One layer of 40# A-S, coated felt. |
|
| In areas with severe weather | Two layers of 30# A-S felt or one layer of 40# (A-S, coated felt) recommended | |
| 8:12 to 20:12 slope | Normal Conditions | Two layers of 30# A-S felt recommended, but one layer of 40# (A-S, coated felt) recommended |
| Heavier/Thicker tile application | One layer of 45# min. A-S, coated felt. |
|
| In areas with severe weather | Two layers of 30# A-S felt or one layer of 40# A-S coated felt acceptable | |
| 4:12 to 8:12 slope | Normal Conditions | Two layers of 30# A-S felt or one layer of 40# A-S coated felt recommended |
| Heavier/Thicker tile application | One layer of 45# min. A-S, coated felt. |
|
| In areas with severe weather | On lower slopes an upgraded underlayment system and/or waterproof membrane is recommended. |
|
| Less than 4:12 slope | All Conditions | At these slopes, tile is considered decorative. A more stringent underlayment, waterproof membrane system, and reduced tile exposures may be required. |
Figure: Underlayment and Batten Layout
- Check manufacturers’ suggested layout procedures. Each manufacturer should supply information regarding batten spacing and kick-strip installation, as well as a layout calculation chart for its product.
- Tiles on shallow slopes must be installed over a waterproof low-slope roof, either built-up or single-ply. In this case, the tiles are mostly decorative, although they do shield the membrane against ultraviolet light, high winds, and mechanical damage.
- Flat concrete tiles should be installed over preservative-treated battens (Eaves Details for Roofing Tile, below). In climates with snow accumulation, install the counter battens over battens that run from ridge to eaves (Underlayment and Batten Layout, above). These enhance drainage and ventilation, and help to keep the roof uniformly cold, which lessens the chance of ice damming.
Figure: Eaves Details for Roofing Tile
Tile installed without battens (right): Check with the tile manufacturer for proper nail type and nailing depth. A continuous cant strip stops water from collecting along raised fascia board. Underlayment should overhang drip-edge and be completely weathertight.
Loading the Roof with Tile
Gable Roofs
On a gable roof, stack the tile to properly distribute the weight of the tile during installation. This avoids overloading the roof framing system at its weakest point, the midspan of the rafters.
- Pick tiles from different pallets to avoid color patterning.
- Starting from the right, lay out the stacks in numbers as shown at left in Loading the Roof, below, beginning with the fourth course. Space stacks about 12 in. apart.
- Repeat the procedure every fourth course. Odd numbers of courses should have two additional tiles for each additional course on each stack along the ridge.
Hip Roofs
Loading a hip roof is the same as loading a gable roof except that the number of tiles in stacks at the far left may vary due to the size of the roof (below).
Figure: Loading the Roof
Cutting Tile
Straight cuts at rakes can be made by scoring a line on the tile, then breaking it with a roofing hatchet. Although this leaves a rough edge, it will be covered by the rake tiles.
Valley and hip cuts. Use a power saw — a cut-off saw or a standard tile saw — and a diamond blade. Tiles may be cut wet or dry. When dry cutting, workers should wear respirators because of the fine dust. Also sweep any accumulated dust off the roof so that it does not stain the tiles or cause a fall.
Tile Roofing for High Wind Zones
In high-wind zones, waterproofing includes:
- Keeping wind-driven rain out.
- Preventing the tiles from getting smashed by wind-borne projectiles or being lifted by high winds.
Solving these requires a waterproofing underlayment beneath the tiles, along with good mechanical fastening.Choosing the right materials. A durable roof starts with the correct tile, underlayment and battens:
- Tile: Concrete and clay roof tiles used in high-wind and hail zones should be rated for impact. The test—FM4473—evaluates tile durability by firing ice balls at a test assembly. Class 3 tiles can withstand impact from 1 3/4-inch-diameter ice balls; Class 4 materials can withstand impact from 2-inch-diameter ice balls.
- Underlayment: Use a synthetic underlayment if possible. Synthetics last longer, weigh less and shed water better than felt.
- Battens: Wood battens are acceptable, but it’s better to use an engineered product that will last as long as the tile, especially in wet climates where the battens may be subject to rot.
Waterproofing
Underlayment. On a concrete and clay tile roof, the underlayment and flashings provide the actual waterproofing.
Figure: Single-Layer Underlayment
Waterproofing the roof deck. For a complete waterproofing system:
- Seal all seams in the roof deck, using one of the following:
- Minimum 4-inch-wide peel-and-stick tape applied over all sheathing joints.
- Closed cell spray foam. This is an alternative to peel-and-stick tape. Apply the foam to all panel joints from the attic side.
- Install synthetic underlayment with all seams taped. Follow the manufacturer’s installation instructions for the underlayment product you are using.
- Integrate the flashing with the underlayment. Metal flashing is required at junctures between the roof and sidewalls, at roof edges, in valleys, and around skylights, plumbing stacks, and other penetrations.
- Apply a waterproofing membrane—such as a continuous peel-and-stick membrane or a 90-lb. cap sheet adhered with hot asphalt—over the underlayment system.
Note that the underlayment serves as a slip-sheet for the peel-and-stick membrane. Applying peel-and-stick directly to sheathing over the entire roof would be simpler, but is not recommended because it cannot be removed for reroofing without damaging the sheathing. In fact, it’s not permitted by some jurisdictions.
Battens. Install tiles over a batten system that provides airflow and drainage. Battens are a good idea even if the tile profile doesn’t require because there are fewer penetrations through the waterproofing membrane. Typically, three corrosion-resistant 8d ring shank nails are needed per 36- or 48-inch batten (24-inch-on-center nailing minimum).
Figure: Batten Layout
Securing Tile
Mortar-set tile is generally not permitted in high-wind zones. Secure tiles with mechanical fasteners and use a two-part foam adhesive to supplement the mechanical fasteners along hips, ridges and roof edges.
Figure: Wind-Resistant Tile Fasteners
- Two fasteners per tile will provide the required uplift resistance for a 130-mph wind zone. Hot-dipped galvanized, ring-shank nails (minimum 10d, or .121 inch, with a 5/16-inch, full-round head) or minimum #8 course-thread screws fit the bill.
- Nails and screws must penetrate the roof deck or batten by at least ¾ inch.
- In a high wind, the most intense uplift pressures on roofing are along eaves edges and along hips and ridges.
- Hurricane clips or twist-wire connectors are also permitted.
- In seismic zones, twist-wire connections have the added advantage that they can absorb some of the shock of a minor earthquake.
Note: all metal components must be compatible.
Figure: Fastening Tile in High-Wind Areas
| Roof Slope | Solid Sheathing with Battens | Solid Sheathing without Battens
|
Eaves Course | Perimeter Tile and Tile on Cantilevered Area
|
|
|---|---|---|---|---|---|
| Fastening required on roofs 40 feet or less above ground (measured to the eaves) in areas with wind velocities up to 80 miles per hour | 3:12 to 5:12 | one 10d nail every tile | one 10d nail every tile | one 10d nail and one clip every tile
|
one 10d nail every tile |
| 5:12 to less than 7:12 | one 10d nail every tile | one 10d nail every tile | one 10d nail and one clip every tile
|
one 10d nail every tile | |
| 7:12 to less than 12:12 | one 10d nail every tile | N/A | one 10d nail and one clip every tile
|
one 10d nail every tile | |
| 12:12 and over | one 10d nail and clip every tile | N/A | one 10d nail and one clip every tile
|
one 10d nail every tile | |
| All slopes | one 12 d nail or two 10d nails and one clip every tile | ||||
| Fastening between 80 and 120 m.p.h. | All slopes | two 10d nails and one clip every tile | |||
Cold-Climate Tile Roofing
In cold climates, build a “cold roof” using counterbattens, whether or not the attic is ventilated.
The steeper the roof, the better. A steeper roof will reduce snow loading as well as promote airflow through the counterbattens.
Counterbatten System
Figure: Cold-Climate Tile Roof
- Use 2x vertical battens with the eaves intake and ridge outlet baffled to keep out wind.
- Depending on snow accumulation and roof pitch, 2x cross battens may be required to support snow loads. In extremely cold and snowy climates, or with long, low pitch (around 4:12) roofs that require more ventilation space to promote airflow, vertical battens taller than 1 1/2 inches (for example, 2x4s on edge) may be required. Be sure to consult an engineer for this application.
- Brackets may be needed to prevent tall battens from tipping under live loads.
- When the attic is ventilated, install ridge boards with standoff brackets to allow attic airflow to exhaust.
- Underlayment. A double layer of 30-lb. felt is considered good practice.
- Ice Protection: In areas prone to ice dams, install a self adhering waterproofing membrane from the eaves to a point 24 inches inside (or above) the exterior wall line. Some code jurisdictions require more ice protection.
Detailing Valleys
Figure: Closed Valley
- While not required by code, peel-and-stick is recommended along valleys.
- Long valleys are difficult to vent.
- Battens that run along the valley should be segmented, and vertical battens should be gapped so they do not intersect the diagonal valley battens.
- Closed valleys using “WW” metal (with added standoffs to support cross battens), will be less likely to get clogged with debris.
- Valley metal for tile roofs should have upturned edges to contain the water flowing down them.
Flashing
Flashing for tile roofing must serve two purposes: 1) to limit the amount of water that gets under the tile, and 2) to keep water out of the roof deck. This requires a dual-layer flashing around penetrations and at roof-wall intersections.
Figure: Flashing Wall Intersections
Figure: Flashing Vent Pipes
In cold climates, vents for combustion heating appliances should be boxed in a chimney to isolate them from the roof and reduce the chance that snow will melt around them. If possible, place the stack high on the roof, with the top of the stack above the ridge to prevent heated exhaust air from blowing across the roof surface and melting snow.
Crickets are a must above chimneys, skylights, and other large penetrations projecting through the roof.
Figure: Flashing Large Penetrations
