Plywood Over Shiplap Roof

Being ideal for asphalt shingles in the early days of its creation shiplap sits beneath the roof of many homes about thirty years old.

Plywood over shiplap roof.

These wider boards were all nailed tightly together. 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. Over time shiplap fir wood resin dissipates causing the boards to shrink crack form knot holes and become extremely brittle. However that isn t the case.

Shiplap is now considered an enemy of asphalt shingles. If the roofing underlayment is applied directly on top of the shiplap it will sag into the spaces and eventually leak. I am sure i am not the only one that has been deceived by what looked like venting but wasn t. As roofing contractors in seattle we are often asked why do we need plywood over our old solid sheathing.

The keyword here is solid it used to be standard to use shiplap 1 boards tongue groove or other boards for the roof deck. In most cases if it is a cold roof shiplap will be fine. Shiplap roof decking was widely used in the 50 through 80 s era when plywood hadn t yet made its way into new construction. Thanks for the heads up.

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. As for slope i haven t actually measured it. At one point in time it was standard to use shiplap tongue and groove one inch boards or other boards for your roofing deck. Shiplap does work but requires good intake exhaust.

Plywood will eliminate the buckling problem completely but still needs to be properly vented. Remember the keyword is solid. Open spaces form between the once tightly fitted shiplap boards. There is another issue whether the shiplap is aiding your household air infiltration.

But since the rafters will be open this plywood will be visible from the patio. Whenever your roof was first installed the nails were put into the solid wood. Today a shiplap roof is usually 60 years old. I was low balling it to see if indeed as the roofer said low slopes necessitate adding plywood over shiplap.

If you have roofers that don t know the difference between shiplap skip sheathing find a roofer that does. These 8 to 12 inch wide boards were nailed together tight. 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.