What Is the Proper Flashing for a Cement Tile Roof?

Cement Tiles

• The cement mix used in tiles is the same as that used in any other application. Portland cement is blended with sand and water -- and sometimes ash -- then coloring or finishing elements are added. For tiles, the cement is then injected into a mold and allowed to cure. Cement tile is typically less expensive than the clay variety, and one of its primary uses is to mimic much more expensive slate.

Tile Variations

• Cement tiles can be simply that -- plain cement -- or they can be glazed or otherwise surfaced. They are available in a limitless array of styles and profiles, each of which may be produced with a number of variations for different purposes: The tiles that fill in the broad surfaces of a roof are called field tiles; ridge tiles cap off the tops of pitched roofs. Terminal tiles are used at the edges of roofs, and hip tiles are mounted where down-sloping angles join. All can be either interlocking or flat.

Flashing Defined

• Flashing describes both the process and the material used to seal the edges of a roof against moisture incursion. Flashing is installed along perimeters, around penetrations -- flues, soil stacks, skylights and other fitments that require a hole in the surface of the roof -- in the valleys and at the top and base of some vertical surfaces.

Flashing Selection

• There is no one universal flashing for cement tile. Perimeter edging is typically made of metal but differs in style and sturdiness, according to the most extreme climatic conditions anticipated. Around penetrations the flashing is extended up-slope beneath the first row of tiles and again is usually made from some type of metal that is shaped or bent to specifications. Valleys and verticals are made from sheet metal. The sheet metal is folded up around a wooden trim, called a “nailer,” after which the entire assembly is shielded by a special cover tile. Metal flashing should be a minimum of 26-gauge and corrosion-resistant. If lead is used around penetrations, it must be a minimum 2-1/2 pounds per square foot. Sheet metal used in valleys must overlap the drip edge by a minimum of 1 inch. Flashing at wall abutments must have a metal skirt that extends under the tile to carry water back onto the field tile; the vertical flange must be at least 5 inches and the base flange at least 6 inches.