Rafter Specifications for Concrete Tile

Concrete Tile Weight

• Concrete roof tiles weigh up to 12 pounds per square foot when properly installed to the surface of a roof deck with mortar and hardware. Asphalt tiles, some of the lightest roofing available, on the other hand, weigh 4 pounds per square foot or less when installed to a roof’s surface. Despite this substantial weight discrepancy, common rafter size and rafter spacing generally provides sufficient support for the installation of concrete roof tiles.

Rafter Size

• Like with the joists in a roof, which may support an attic floor on top and ceiling surface on the bottom, roof rafters are created out of standard-sized boards. While roof joists commonly have widths of only 6 or 8 inches, roof rafters generally have widths of at least 10 inches. Two-by-10-inch or 2-by-12-inch wood boards may be cut down to span the distance from the side of the walls around the roof to the top roof beam to create the rafters.

Spacing

• Like joists in a roof, roof rafters also typically install using standard spacing. The 2-by-10 or 2-by-12 boards cut for rafters are generally spaced 16 inches on center. To install boards with this spacing, you must mark the walls on either side of the roof and the roof beam every 16 inches, then place each rafter so it sits centered over the mark, with 1 inch extending on either side of the mark.

Weight Limits

• Standard 2-by-10-inch rafters spaced every 16 inches on center provide roughly 20 pounds of support per square foot. So, laying roof rafters out at the standard specifications allows for safe installation of concrete tile. However, in some instances, it may be advisable to add additional support to the roof deck before installing concrete tiles. In some localities, building codes may require closer rafting spacing for concrete tiles. Closer rafter spacing also can beneficial in regions that get severe weather, so that when snow and ice piles on the roof, the roof can support the accumulation along with the weight of the concrete tiles.