Plywood Over Shiplap Roof

Thanks for the heads up.

Plywood over shiplap roof.

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. Shiplap roof decking was widely used in the 50 through 80 s era when plywood hadn t yet made its way into new construction. 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 is now considered an enemy of asphalt shingles. The keyword here is solid it used to be standard to use shiplap 1 boards tongue groove or other boards for the roof deck. Shiplap does work but requires good intake exhaust. After the 1960s the predominant residential roofing substrate became 1 2 cdx plywood.

But since the rafters will be open this plywood will be visible from the patio. Shiplap doesn t have any gaps in the boards and can be roofed over as is usually. However that isn t the case. Plywood will eliminate the buckling problem completely but still needs to be properly vented.

As for slope i haven t actually measured it. Over time shiplap fir wood resin dissipates causing the boards to shrink crack form knot holes and become extremely brittle. Open spaces form between the once tightly fitted shiplap boards. 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.

These 8 to 12 inch wide boards were nailed together tight. Whenever your roof was first installed the nails were put into the solid wood. 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. Remember the keyword is solid.

In most cases if it is a cold roof shiplap will be fine. As roofing contractors in seattle we are often asked why do we need plywood over our old solid sheathing. Today a shiplap roof is usually 60 years old. There is another issue whether the shiplap is aiding your household air infiltration.

I was low balling it to see if indeed as the roofer said low slopes necessitate adding plywood over shiplap. 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. Being ideal for asphalt shingles in the early days of its creation shiplap sits beneath the roof of many homes about thirty years old.