Sheathing Over Trusses
The first thing the roofer checks is the framers' sheathing. Panels should be staggered, gapped about an eighth of an inch for expansion, supported with H-clips between trusses where required and nailed on the schedule the inspector expects. Missed nails and blowouts at the truss tops get fixed now, not after the shingles are down.
H-clipsPanel gappingNailing schedule
Slope and Material Matching
Shingles are rated down to 2:12, but between 2:12 and 4:12 the underlayment has to be doubled. Below 2:12, the roofer will usually point you toward a membrane such as modified bitumen or TPO, or a metal system rated for low slope. Getting this wrong on a porch or sunroom roof is a common source of slow leaks.
Minimum pitchLow-slopeDouble underlayment
Additions and Tie-Ins
A proper tie-in means peeling back the old courses, lapping new underlayment beneath them and sealing the seam with ice barrier. Where the new roof meets a wall, step flashing goes in course by course with a kickout at the bottom. Matching shingle color on an older roof is rarely perfect, so ask to see samples.
Tie-inKickout flashingCricket
Starter Course and Edge Details
The order matters: drip edge at the eaves sits under the underlayment, while at the rakes it goes over. A factory starter strip with its sealant line along the eave keeps the first course from lifting, and running starter up the rakes helps in wind. These are small parts, but missing them is something the shingle maker can point to later.
Drip edgeStarter stripRake edge
Valley Styles
Open metal, closed-cut and woven valleys are the three main options, and the manufacturer instructions say which ones they accept. Closed-cut is the most common look on new homes. Open metal valleys move the most water and suit roofs where a big upper slope dumps into a smaller one. Woven valleys do not work with many thick laminated shingles.
Open valleyClosed-cutWoven
Skylight Curbs and Penetrations
On a new roof, skylights should sit on curbs or factory flashing kits, set before the shingles go around them. Plumbing vents, bath fan hoods and the furnace flue all need boots or flashing that match the pitch. The roofer should coordinate with the plumber and HVAC crew so nobody cuts a fresh hole through a finished roof.
Skylight curbPipe bootsFlue flashing