Sheet Size and Weight
Each sheet measures 48 inches by 79 inches long, covering an area of 26.33 square feet. The ridged, corrugated sheets are 1 3/8 inches thick and weigh 18 pounds. The weight per square is 81 pounds. A square is 100 square feet. To calculate the sheets needed per square, divide 100 square feet by 26.33. This yields 3.8 sheets to make one square. Ondura recommends rounding the estimate up to four-and-a-half sheets per square to allow for waste.
Ondura recommends using specially designed 3-inch nails to install the material. Each sheet will require 25 nails, but Ondura recommends allowing for 26 nails per sheet in case of waste. The nails should be spaced equally across the purlins.
Purlins--thin cross pieces of lumber, nailed perpendicular to the rafters to support the panels--should be spaced 24 inches apart on center to support the roofing material. For heavy snow areas, Ondura recommends spacing the purlins 12 to 18 inches apart.
A circular saw with a carbide-tipped blade should be used when cutting across the panels. Ondura recommends using a sharp utility knife to cut parallel to the corrugations.
The minimum slope recommended for Ondura roofing is 3/12. Slopes for roofs are stated in a rise-over-run format. In a 3/12 roof, the vertical rise is 3 inches for every 12 inches of horizontal run. To picture this, suppose a shed is 10 feet wide. The peak of the shed's roof will be centered--5 feet from the front of the shed, 5 feet from the back of the shed. Each 5-foot measurement represents a group of five 12-inch runs. If the rise is 3 inches per every 12 inches of run, multiplying 3 inches of rise times the five groups of 12-inch runs yields 15 inches. The roof peak, then, is 15 inches above the top of the wall line. The smaller the rise number, the shallower the roof. A 0/12 roof is flat. A 12/12 roof has a 45-degree pitch. An 18/12 has a very steep pitch, like a European chalet.
Ondura roofing should be installed starting at the bottom roof line, working up to the top. Sheets should overlap by at least 7 inches on the short side of the panel, with the uppermost panel overlapping the lower panel. Sheets should overlap by the width of one corrugation on the sides.