The Installation of a Tile Roof Without Plywood

OSB

• The use of OSB instead of plywood for roof decks began in the early 1990s. Made largely in the United States and Canada, OSB consists of thin, rectangular strips of wood pressed together and bonded with wood resin and wax. It has properties similar to plywood, but it is more uniform and less expensive. OSB is not impermeable, but it can be used for roof decks with tiles because it is protected by both underlayment and tiles. The NRCA says that if OSB becomes saturated with moisture the nails or screws used to fasten tiles onto the deck may loosen.

Tongue and Groove

• The edges of T&G boards fit together so they make a strong flat surface. A thin, deep ridge, the tongue, is cut on one edge of a board. A matching slot, the groove, is cut along the opposite edge. The tongue of one board is fitted into the groove of the adjoining board. T&G makes sturdy roof decks, but they are expensive to make and install. A T&G deck made of 2-by-6 lumber does not need additional insulation in moderate climates. It can be painted or stained to match the interior if there is no ceiling beneath the deck.

Dimensional Lumber

• The boards of dimensional lumber are usually 4 to 8 inches wide and 3/4-inch thick. When used to make a deck for tiles they are installed side-by-side parallel to the roof slope. They are not as costly as T&G lumber, but like T&G the labor costs of installing a dimensional lumber roof are far greater than those for plywood.

Special Considerations

• The NRCA recommends that wood used on roof decks be dried by a kiln or in the air or be treated with a non-oil preservative applied under pressure. Some wood treated with chemical fire retardants will decay under wet or humid conditions. Do not use lumber treated with an inorganic salt fire retardant that is intended for dry interiors only. Make sure the retardant is specifically formulated for use on weather protected exterior use.