Use this skill when the user needs shingle replacement, leak repair, flashing installation, or any work on a roof surface. Triggers include: 'my roof is leaking', 'missing shingles after the storm', 'I need to reflash the chimney', or 'how many squares do I need'. Do NOT use for 'raise the roof' or any other metaphorical roofing.
A residential asphalt shingle roof is a layered system: decking (plywood or OSB sheathing), underlayment (synthetic felt or ice-and-water shield), drip edge metal at the eaves and rakes, and shingles installed from the eave upward in overlapping courses. Each layer sheds water to the layer below it. The system works only when every layer is intact and properly lapped. One reversed lap or lifted shingle and water gets behind the system.
Roof work is performed at height on a sloped surface. Falls from residential roofs are the leading cause of fatality in construction. Do not begin work without appropriate fall protection, a stable ladder, and favorable weather — no rain, no frost, no wind above 15 mph.
Roof leaks rarely appear directly below the breach. Water enters at a penetration or lifted shingle and runs along the underside of the sheathing, rafters, or ceiling joists before dripping onto the drywall. The stain on the ceiling may be several feet from the actual roof penetration.
Start from the attic if accessible. During or immediately after rain, go into the attic with a flashlight and trace the water. Follow the wet trail uphill along the rafters to the point where it first appears on the underside of the sheathing. Mark this spot by pushing a nail or wire up through the sheathing so you can find it from the roof surface.
If no attic access, work from the exterior. Common leak sources in order of likelihood: pipe boots (the rubber flanges around plumbing vents), chimney flashing, step flashing where the roof meets a wall, valleys, and damaged or missing shingles. Inspect each systematically.
Each shingle has two nail lines: one concealed by the shingle above it, and the visible exposure below the tab line. To replace a shingle, you must access both its nails and the nails of the shingle above it that pass through the top edge of the damaged shingle.
Asphalt shingles have a thermally-activated adhesive strip that bonds each course to the one below it. On a warm day, carefully slide the flat pry bar under the shingle above the damaged one and pry upward to break this seal. Work slowly — aggressive prying will crack the shingle above, creating a second problem.
In cold weather (below 40°F), shingles are brittle. Warm the sealant line with a heat gun before attempting to break it, or wait for a warmer day.
Each three-tab shingle is held by 4 nails (6 in high-wind zones). They are located approximately 1" above each tab cutout and 1" from each end. Slide the pry bar under the damaged shingle, locate each nail head by feel, and lever it out. Then lift the shingle above and remove the nails that pass through the top edge of the damaged shingle.
Slide the new shingle into position, aligning it with the adjacent shingles so the tabs are consistent and the exposure (the visible portion) matches the surrounding courses — typically 5" or 5-5/8" depending on the shingle type.
Nail the new shingle following the manufacturer's nailing pattern. The nails should penetrate through the shingle, through the underlying shingle's top edge, and into the sheathing. Each nail should be driven flush — not countersunk (the nail head should not break through the shingle surface) and not proud (sticking up, which creates a bump under the shingle above).
Seal the lifted shingles back down. Apply a quarter-sized dab of roofing cement under each tab that was lifted, and press firmly. The sun will eventually reactivate the adhesive strip, but the cement provides immediate hold.
Chimney leaks are the most common call for roof repair. The flashing system around a chimney consists of step flashing (L-shaped pieces woven into the shingle courses along the sides), base flashing at the front, counter flashing (embedded in the mortar joints and folded down over the step flashing), and a cricket or saddle on the uphill side to divert water around the chimney.
If the counter flashing has pulled away from the mortar joint, clean out the joint to a depth of 1" with an angle grinder and a diamond blade or a cold chisel. Press new counter flashing into the joint and seal with high-temperature urethane caulk. Tuck-point the joint with mortar for a permanent repair.
If the step flashing itself has failed, the shingles along the chimney must be removed to access and replace the step flashing pieces. Each piece should extend at least 4" up the chimney wall and 4" under the shingles, with each piece overlapping the one below it by at least 2".