Why do we need to resheet over the existing shiplap on my roof?

Was Your Roof Build With Ship-Lap?

If you have an older home built prior to 1970, then you may be wondering why your roofing contractor is wanting to re-sheet your roof deck before installing your composition shingles. This is most likely because your roof was build using shiplap as a solid substrate for the roofing system.

The Era Of Ship-Lap

Shiplap (1×8 fir wood) was pre-plywood and was used to create a solid substrate for composition shingles.  Until the 1940s, exterior grade plywood was not available and since the boards used for shiplap were manufactured here in the Pacific Northwest, it was still cheaper to use than plywood. Through the 1960s, a typical residential home construction did not use plywood, but ship-lap.

The Condition Of The Roof Deck

After the 1960′, the predominant residential substrate was 1/2″ CDX plywood. When we run across a roof that has ship-lap, we are encountering wood that is 60+ years old. It is not that the 1×8 fir wood is rotted, but the resin has dissipated out of the wood causing Re-sheeting over Shiplapthe boards to shrink and become extremely brittle. Evidence of this, are the cracks in the boards, as well as knot holes in the wood where there is shrinkage. Also due to this reduction in size, there are now open spaces between the once tightly fitted boards of the shiplap. If the underlayment is applied directly on top of the shiplap, it will sag into the spaces and eventually leak. It is also not uncommon for older homes to have multiple layers of roofing over the original, causing the wood to be splintered and inconsistent due to previous nails. This and the space left by diminished overall size over the years, creates more opportunities for the new nails to miss the wood completely, causing eventual leaks.

Installing The New Roof

When installing the new composition shingles, utilizing EG nails, when the nail penetrates into the board, the board will crack and split not seating around the nail properly. Without the nail being properly secure, through expansion and contraction, the nail will work upwards pushing through the freshly installed shingle. This action will create migratory seepage and mystery leaks, due to the raised nail head. When installing the shingles properly, in a straight line, over a 16 foot rise, there will be a few courses that will land on the 7 1/2″ increment while installing the shingles. That being said, you can have an entire course of shingles that are not secure due to lining up with the natural crack created by the ship-lap.

Creating A Solid Substraight

why do I need to re-sheet my shiplap roof deckWith all this being said, why take the risks of installing a 50 year roof, just for it to leak in 5 – 10 years? If you want to avoid the headache of tearing up your new roof looking for a mysterious leak that “should not be happening”, it is in your best interest to apply solid sheathing over the existing shiplap to create a solid substrate for your roofing system. The recommended materials are exterior grade 7/16″ OSB (oriented strand board) or 1/2″ CDX true plywood.

Don’t Take Shortcuts When Protecting Your Biggest Investment – Your Home!

You want to steer clear of contractors that would want to cut corners, and if you find one that says it’s ok to install a composition roof on top of skip-sheathing, give them a no thank you! Your roof, and peace of mind will thank you in the future! At Chase Construction NW, Inc., we never cut corners! We care about our customer’s experience, now, 5, 10, 20 years down the line! That is why we only recommend what is best for you and your roof. You need to protect your biggest investment, your home! And taking the cheapest route, isn’t always the best, why take the risk?

Contact Us Today!

Seattle Roofers

If you are looking for an honest, knowledgeable, and experienced roofing contractor, we are here for you! Contact us today for your free estimate! Call 253.445.8950, or fill out our quick estimate form! We look forward to working with you!

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