Home builders once used 1×8 spruce planking to cover the roof trusses of a new home under construction. That was once.
The strategy basically involved the following. Build the retaining walls for the poured concrete foundation using 1×8 spruce lumber. Then, once the cement was dry, the spruce planking would be removed and used as sheeting material over the roof trusses. One product, serving two purposes, and although a little labor intensive, produced hardly any clean-up or waste to speak of. In those days we also put chains on our summer tires for better winter traction, used rotary phones, and thought lawn darts to be a great summer game for the whole family.
Times have changed. Winter tires have become the standard, rotary phones are about as common as a Stanley cup parade down Yonge Street, while lawn darts have been taken off the retail consumer shelves completely, having been remarketed as the preferred weapon of choice for those low-budget mercenary types.
Was the use of 1×8 spruce planking as a roof sheeting a bad idea? In retrospect, no. Back then we were roofing homes with what was known as an organic shingle, due to its base consisting of a mixture of asphalt and wood fibers. Organic shingles were flexible, and molded themselves easily over the not so perfect 1×8 planking. Plus, warranties back then were in the 10-15 year range. So, if a roof lasted 10-12 years or so, people were generally satisfied. If tearing off these old shingles and replacing them with new ones seemed excessive, people would simply re-roof, adding a second, or even third layer of asphalt shingles. If the homeowner chose to go with steel roofing, as opposed to asphalt, then the steel would either get screwed directly to the planking, or the installer would first install 1×4 rough spruce, spaced every 16-24 inches, over the existing 1×8 planking. Either way, emphasis concerning the protection of one’s home was placed on the surface product, not so much on the substrate.
Today, roofs occasionally leak. In the olden days, they leaked a lot. Why roofs leak less today has everything to do with the substrate, along with better education and information relating to proper venting, and attic insulation. So, what have we learned over the years? 1×8 spruce lumber will expand, shrink, and with prolonged exposure to water, will of course rot. However, the main knock against the old plank system is the issue of movement. You can’t install something that doesn’t want to move, like fiberglass shingles, or steel roofing, over something that naturally, due to our varying climate and atmospheric conditions, can’t stay still. That would be like wrapping a puppy in gift paper, setting it under the tree Christmas Eve, and expecting it to stay still, without wrinkling or tearing the wrapping paper, until the surprised recipient picks it up the next morning.
When the substrate moves, screws loosen, nails pop, and when the shingle tiles separate from each other, or in the case of steel roofing, the overlap on the ridge develops a gap, your roof will no longer be water impermeable.
The first sign of a breach in the roofing system is the decorative sunburst that develops on your ceiling, or a domed ceiling fixture filled with water, enabling you to create the very unique ceiling fish bowl (just don’t turn on the power).
The key to a roof’s long term success in shedding water is stability, and that can only be achieved by nailing or screwing it into plywood. So, if you own a home with a boarded roof, be sure to remove all existing shingles, then fasten a layer of 3/8” spruce plywood directly to the 1×8 lumber. Next, cover this plywood with a quality synthetic felt, then install the required roof venting. Your roof is now ready to receive the finished product.