Soft spots underfoot? Roof decking replacement in Vancouver, WA

Roof decking, also called sheathing, is the layer of plywood, OSB or old board planks nailed to the rafters. Shingles and underlayment sit on top of it, and nails have to grip it to hold the roof down in wind. When decking gets wet over and over, it softens, swells, delaminates or rots. Shingles laid over bad decking will not seal flat, and nails pull loose.

Decking replacement is part of most leak repairs that have gone on too long, part of many full roof replacements, and sometimes a job on its own. We find the extent of the damage, cut the bad wood back to solid framing, install new sheathing of the right thickness, and rebuild the roof surface. If we find the cause, such as a leak or poor ventilation, we fix that too.

What causes roof decking to fail

Most decking damage comes from water that sits in the wood for a long time. A slow leak at a pipe boot, valley or chimney can soak the same patch of sheathing every rainy season for years before a stain shows up inside. Gutters that overflow along the eaves soak the lower edge of the decking. In both cases, the wood darkens, softens and loses its grip on nails, and the damage keeps growing quietly until someone steps on it.

Attic moisture is the other big cause. When warm, damp air from the house rises into a poorly vented attic, it condenses on the cold underside of the decking all winter. OSB is especially prone to swelling and flaking when that happens year after year. You may see black staining across large areas of the attic, frost on nail tips on cold mornings, or a wavy roof line from outside as the sheathing swells between rafters.

How we find and replace bad decking

From the roof, we walk the surface and probe soft areas. From the attic, we look for dark stains, flaking layers and nails that have rusted or pulled through. Once we expose the decking, we test the wood around the damage with an awl, since rot often spreads farther than it looks. Every bad section is cut back to the center of the nearest rafters so new sheets have full support on both edges.

• Probe and mark soft areas from above
• Check the attic for stains and flaking layers
• Cut back to the centers of solid rafters
• Install sheathing matched to the existing thickness
• Use clips or blocking where the framing needs it

Plank decking on older Vancouver homes

Many early 1900s homes and Craftsman bungalows near downtown Vancouver have board planks instead of plywood. Those boards were often laid with gaps for the wood shingles that topped them originally. Composition shingles need a solid surface, so when we reroof these houses, we often add a layer of plywood over the planks or replace the worst boards. We check plank condition carefully, since a single cracked board can leave a weak line across the roof.

Some mid-century homes have plywood that has delaminated over decades, especially near the eaves and around old chimneys. It may look fine from below but lose strength where it matters. When a roof is off for replacement, we inspect every sheet and replace the ones that fail. We tell you the count and show photos before we close it up, so there is no guessing about what was replaced and why.

Fixing the cause so it does not come back

New decking will rot just like the old if the moisture source stays. If the damage traces back to a leak, we repair the flashing, boot or valley at the same time. If it comes from attic moisture, we look at soffit and ridge vents, bath fans venting into the attic, and gaps in the ceiling that let warm air rise. A decking repair that ignores the cause is a temporary fix, and we will tell you that up front instead of hiding it.