How are architectural shingles installed?
Short answer. Architectural shingles go on over a sound deck with drip edge, underlayment and membrane in valleys and at walls, then a starter strip along the eaves and rakes, followed by courses laid from the bottom up at the manufacturer's exposure and offset, nailed in the marked nailing zone, and finished with new flashing, vents and hip and ridge caps. The details that decide how long the roof lasts are nail placement, flashing and ventilation.
Order of installation
- Tear-off and deck check: remove old roofing down to the deck, replace soft or damaged sheathing, and renail loose panels.
- Eave drip edge.
- Membrane and underlayment: self-adhered membrane in valleys and around walls and penetrations, synthetic underlayment over the rest.
- Rake drip edge over the underlayment.
- Starter strip along the eaves and rakes, giving the first course a sealant line and stiffening the edges against wind.
- Field shingles from the bottom up. Most standard laminated shingles have an exposure of about 5 5/8 inches, and the maker specifies the offset between courses.
- Nailing: typically four nails per shingle, more where high wind application is specified, placed in the nailing zone and driven flush.
- Valleys: closed-cut, woven or open metal, as the manufacturer allows.
- Flashing: new step flashing at walls, chimney and skylight flashing, pipe boots and kickouts.
- Ventilation: ridge vent or other exhaust balanced with soffit intake.
- Hip and ridge caps: purpose-made cap shingles, with the last nails sealed.
What to watch for
- Nails high, crooked or overdriven.
- Old flashing reused under new shingles.
- No starter at the rakes.
- Shingles on a slope below 2 in 12, which the code does not allow, or between 2 and 4 in 12 without double underlayment.
Every manufacturer prints its instructions on the bundle wrapper, and following them is what keeps the warranty valid. See architectural vs 3-tab shingles, synthetic underlayment vs felt and replacement day.