Osb Over Existing Sheet Metal Roof

A homeowner recently wrote and asked me the following regarding osb roof decking.

Osb over existing sheet metal roof.

This is by far the most common way to install a metal roof. Thicknesses range from 5 16 to 3 4 inch and the proper one to use. Osb comes in 4 by 8 foot sheets as does plywood but the manufacturing process allows the production of longer and wider ones. Table 2304 7 3 gives the 7 16 osb the ability to carry a roof live load of 40 psf pounds per square foot when spanning the same 24 inches.

In the case above the shear forces in the last 12 foot bay at each end of the roof have had osb placed between the roof purlins and the steel roofing. Osb is widely used as roof decking material. If there are gutters installed on the eaves the eave flashing should be installed to overhang the lip of the gutter by about 1 2 inch. From the 2012 ibc international building code table 2304 6 1 over framing spaced 24 inches on center 7 16 osb fastened with 8d common nails six inches on center at the edges and in the field will support a maximum design wind speed vult of 110 mph miles per hour in exposure b or 90 mph in exposure c.

Stagger the panels over the roof with 2 supports between panel ends. Today a shiplap roof is usually 60 years old. After the 1960s the predominant residential roofing substrate became 1 2 cdx plywood. When the steel roofing can t carry the load other shear carrying materials such as 7 16 osb may be added to the assembly.

Open spaces form between the once tightly fitted. Roof trusses must be dry when sheathing a roof with osb to prevent mold growth in the roof and coverage gaps as the trusses dry and shrink. 3 install 1 4 purlins down over the shingles before installing the metal roof the third way to install a metal roof over shingles is by applying 1 4 purlins over the shingle roof. As long as the plywood under the shingle roof is in good condition this way can provide many benefits.

Place corner pieces where panels will meet bends at the edge of the roofing. Over time shiplap fir wood resin dissipates causing the boards to shrink crack form knot holes and become extremely brittle. Use 1 1 4 inch nails to cover the outline of the roof with strips of metal eave flashing also called edging.