Plywood Over Plank Roof

In the first half of the 20th century roofs in missouri were built with wood shingles over planks spaced about 1 apart.

Plywood over plank roof.

These 8 to 12 inch wide boards were nailed together tight. As roofing contractors in seattle we are often asked why do we need plywood over our old solid sheathing. After the 1960s the predominant residential roofing substrate became 1 2 cdx plywood. It was common practice to have a clause in the contract that once the roof was stripped down depending on what was found plank roofs that were not already covered with plywood would then need to be covered in order to do a good job and provide a solid warranty.

Its really common here too to see 3 8 plywood used on roofs from the 70 s. In that case they could whe replacing shingles fill the larger gaps with firring. Or they could place osb or plywood over current planking. Plywood is layers of wood plywood is made.

Open spaces form between the once tightly fitted shiplap boards. We resheet with 1 2 osb right over top of the old all the time be it 3 8 ply or old t g boards in the case of the old t g boards it makes for a flatter surface plus greatly lessons the chance of nailing into the gap between boards. Personally i like plank spaced decking. On older homes planks were often spaced for wood or slate roofs with wider exposures than the standard 5 inch tab on asphalt shingles.

This is particularly important if your old sub floor has lumps and bumps in it. The plank problem typically sheathing problems are isolated to small areas but old plank sheathing presents more of a challenge. Plank sheathing usually 1 6 or 1 8 was used as a roof deck before plywood. Take time to make sure your existing planks are well secured in place.

Over time shiplap fir wood resin dissipates causing the boards to shrink crack form knot holes and become extremely brittle. Things to take into account when laying ply over plank subfloors. Today a shiplap roof is usually 60 years old. Most western washington residential homes during this time were built with shiplap roof decks rather than plywood.

Repair any broken planks. Why re sheet over shiplap. Use decking screws to secure squeaking planks through 1 4 ply to joists. Use door skins to raise dips to 1 8 use contact cement to secure to existing 1 4 ply secure 17 32 plywood to the planks with 1 5 deck screws avoiding the joists to allow slip install engineered hardwood over the new subfloor w underlayment if needed.

Plywood used for roof decking is typically called sheathing and carries a grade stamp indicating its load and span ratings and other performance factors. But the spacing should not be more than quarter inch.