One 4′ x 8′ sheet of 7/16″ O.S.B. (ORIENTED STRAND BOARD), weighs 47 lbs.
One 4′ x 8′ sheet is equal to 32 sq feet. Three sheets are equal to 96 sq feet, you will need 3 ¼ sheets to do a roofing (10′ x 10′) square….adding 153 pounds of weight to the roof’s square.
(A 4′ x 8′ sheet of ¾” plywood will weigh 75 lbs or 245 pounds per roofing square.)
A roofing square of dimensional shingles has an average weight of 300 pounds per square. A house can easily handle the combined weight (430 pounds per square) of a new roof deck and 30 year shingles. Building code calls for structural weights of 1,000 pounds and more.
Plywood is better suited for humidity, and has better nail pull resistance, but adds $2.00 per sheet more than O.S.B., or 8.00 additional per square, which is why we contract for O.S.B. whenever we can, to save our customer’s money.
When a piece of wood needs to be totally removed and replaced, we will use the O.S.B. and charge 50.00 per sheet, for our labor, the material, and the time involved getting it back to the job site. IF your home has linear plank decking, we charge 6.00 per foot replacement cost. Wood charges are added to the final bill due.
When all the deck is weakened structurally, or the plywood is DELAMINATING from moisture (humidity, leakage), we can SHEET OVER the existing roof deck. When we do this, the cost of ALUMINUM Gutter and Rake FLASHING must be added into the cost of the re-sheet, as well as an additional 50.00 (per 25sq) box of EIGHT PENNY deck nails. Because we are raising the new deck UP higher than the GUTTER and RAKE fascia boards, we must wrap the visible wood edge, or water will attack and cause it to swell up in only a few years time.