Plywood Over Shiplap Roof

Sometimes on older houses they have had so many different roofs that the deck is all shot up splintering in this case a redeck is in order.

Plywood over shiplap roof.

As roofing contractors in seattle we are often asked why do we need plywood over our old solid sheathing. These 8 to 12 inch wide boards were nailed together tight. As for slope i haven t actually measured it. I was low balling it to see if indeed as the roofer said low slopes necessitate adding plywood over shiplap.

I am sure i am not the only one that has been deceived by what looked like venting but wasn t. At one point in time it was standard to use shiplap tongue and groove one inch boards or other boards for your roofing deck. Today a shiplap roof is usually 60 years old. Being ideal for asphalt shingles in the early days of its creation shiplap sits beneath the roof of many homes about thirty years old.

Shiplap doesn t have any gaps in the boards and can be roofed over as is usually. There is another issue whether the shiplap is aiding your household air infiltration. Thanks for the heads up. Plywood will eliminate the buckling problem completely but still needs to be properly vented.

After the 1960s the predominant residential roofing substrate became 1 2 cdx plywood. The shiplap does look like its in good condition however i haven t put nails into it or given it any other test of strength. However that isn t the case. If you have roofers that don t know the difference between shiplap skip sheathing find a roofer that does.

Shiplap roof decking was widely used in the 50 through 80 s era when plywood hadn t yet made its way into new construction. In most cases if it is a cold roof shiplap will be fine. The keyword here is solid it used to be standard to use shiplap 1 boards tongue groove or other boards for the roof deck. If the roofing underlayment is applied directly on top of the shiplap it will sag into the spaces and eventually leak.

Over time shiplap fir wood resin dissipates causing the boards to shrink crack form knot holes and become extremely brittle. I m building a solid patio roof and was planning on using 1 2 plywood over the rafters 24 oc for the roof with spruce shiplap over the eaves to match existing house look. But since the rafters will be open this plywood will be visible from the patio. Shiplap is now considered an enemy of asphalt shingles.

These wider boards were all nailed tightly together. Open spaces form between the once tightly fitted shiplap boards. If it is a hot roof and the design assumes airtight sheathing it would be easy at this point to install plywood zip sheathing and tape it.