What Are the Specs on Laying Out a Clay Roof?

Regulations

• Roofing contractors first turn to local codes for the regulations regarding the use of clay roofs. If such rules are missing or inadequate, contractors rely on state codes, or they consult federal statues. These codes will be similar because they are formulated from the International Residential Code, or IRC, which the International Code Council develops and maintains. This nonprofit organization helps the “building safety community and construction industry provide safe, sustainable and affordable construction” across the United States. The council also handles other residential housing guidelines, such as the International Fire Code, the International Plumbing Code and the International Energy Conservation Code.

Basics

• Regulation 905.3 of the 2012 IRC specifically defines clay tile requirements for roof coverings. It mandates installation of the tile only over solid sheathing or spaced sheathing boards. The deck must rise at least 2 1/2 units for every 12 units it moves horizontally, which is a slope of 2.5:12. Slopes up to 4:12 must double the required underlayment. If an area experiences high winds above 110 miles per hour, the underlayment requires corrosion-resistant fasteners attached according to manufacturer’s instructions. If wind speed exceeds 120 mph, the underlayment must be attached in a grid pattern of 12 inches between side laps, which need 6-inch spacing.

Application

• Clay tile must be fastened according to the manufacturer’s installation instructions, with at least one fastener per tile. If the tile weighs less than 9 pounds per square foot, then the minimum fastening requirement applies to all slopes. If the wind speed exceeds 100 miles per hour on buildings where the roof is more than 40 feet above grade, each tile requires a minimum of two fasteners, even if the manufacturer recommends just one fastener.

Flashing

• The edges where vertical roof surfaces meet are called junctures, and they require flashing and counterflashing. If these protections against leaks are made of metal, they must be at least 0.019 inches thick and corrosion resistant, such as No. 25 galvanized sheets. Valley flashings must extend at least 11 inches from the centerline in both directions, and they must have a splash diverter rib that is 1 inch high at the flow line formed as part of the flashing. The end lap must be at least 4 inches wide.