Roofing Nail Patterns, Starter Strips and Details That Matter
Two roofs on the same street in Sun Prairie, same shingle, same year, same builder. One is fine at 22. The other lost half a slope in a June windstorm at 14 and has ice-dammed at the eave every winter since 2015. The difference is not the shingle. It's the roofing nail pattern and a dozen other details that take a crew an extra hour and cost the homeowner nothing if the roofer already does them. This is what they are and how to see whether your roof got them.
Roofing nail pattern: how many and where
A shingle manufacturer's standard nailing is four nails per shingle. The high-wind nailing pattern is six. On paper, four nails is enough for a 110 mph rating and six gets you to 130. In practice, the difference in Madison shows up in the fourth or fifth spring windstorm, when a four-nail roof starts shedding tabs on the west slope and a six-nail roof doesn't.
Placement matters as much as count. Every architectural shingle has a nail line, a strip an inch or so wide where the nail passes through both the exposed layer and the top of the shingle below it. Nails above the line miss the lower shingle and hold only one layer. Nails below the line are exposed to weather. A crew running a nail gun fast on a steep roof drifts high. On a roof that's losing shingles young, pull one and look at where the holes are.
The gun pressure matters too. Overdriven nails cut through the mat; underdriven nails hold the next shingle up and wear a hole in it. Both are a leak in year eight.
Starter strip
The first course at the eave, and the edge courses along the rakes, have no shingle below them to seal to. A starter strip is a purpose-made strip with its adhesive line at the bottom edge, so the first course bonds to it and the wind can't get under. The old shortcut is a regular shingle turned upside down, which puts the adhesive in the wrong place. On a roof that loses its bottom course in every storm, that's usually why. Starter along the rakes, not just the eaves, is the difference between a roof edge that stays put and one that lifts.
Drip edge, and which goes on top
Drip edge is the metal at the roof edge that kicks water into the gutter instead of behind it. The order matters: at the eave, the drip edge goes on the deck first and the underlayment goes over it, so water running down the underlayment ends up on the metal. At the rake, the underlayment goes on first and the drip edge over it, so wind-driven rain can't get under. Reverse either one and water runs behind the fascia. A lot of fascia rot in Westmorland and Eastmorland traces back to a drip edge installed backward twenty years ago.
Ice-and-water shield: how far
Wisconsin's code calls for an ice barrier at the eaves — commonly from the edge to at least 24 inches inside the exterior wall; ask the roofer how far up yours will run. On a house with a two-foot overhang, that's about four feet up the slope, which one three-foot roll doesn't reach. So some crews run one course and call it done. On a low-pitch roof, or one with an ice dam history, many roofers here run two courses or more, and always full-width in the valleys and around every penetration. Ask a roofer how many feet, not whether.
Underlayment and the laps
Synthetic underlayment over the rest of the deck, lapped so the upper sheet is over the lower one, and cap-nailed, not stapled. Felt is legal and cheaper and wrinkles overnight in lake humidity; every wrinkle telegraphs through the shingles.
Valleys
An open metal valley, or a closed-cut valley over ice-and-water shield, both work if done properly. What doesn't work is a woven valley on a heavy architectural shingle: the thick shingles don't lie flat, and the humps trap ice. And no nails in the valley center. A nail within six inches of the valley line is a leak.
Flashing that's new, not reused
Step flashing at every wall, one piece per shingle course, woven in. Counter-flashing at chimneys cut into the mortar joint, not caulked to the face of the brick. A kickout flashing at the bottom of every roof-to-wall joint so the water goes into the gutter, not down the siding. New pipe boots. A crew that reuses 20-year-old flashing to save an hour has given you a 20-year-old leak on a new roof.
The ridge
A ridge vent needs a slot cut through the deck on both sides of the ridge, about an inch each. Ridge vents nailed over an uncut deck are common on 2000s builder roofs; the attic can't breathe and the shingles cook. Then ridge cap shingles over the vent, nailed long enough to reach through the vent into the deck.
Ventilation math
Codes commonly call for 1 sq ft of net free vent area per 150 sq ft of attic floor, or 1 per 300 with balanced intake and exhaust (or a vapor retarder). Intake without exhaust does nothing. Exhaust without intake pulls conditioned air out of the house. Baffles at every rafter bay so the insulation doesn't block the soffits. This is the detail that decides whether a Madison roof ice-dams.
How to check your own roof
From the ground: is there a distinct starter strip visible at the eave? Does the drip edge sit over the fascia cleanly? Is the ridge vent continuous? From the attic: is there daylight at the soffits and at the ridge slot? Are the nail tips coming through the deck evenly, without a scatter of them near the eaves?
Questions to ask about the details
- How many nails per shingle, and will you follow the high-wind pattern?
- Is the starter strip a purpose-made product, and does it go on the rakes too?
- Which goes first at the eave, the drip edge or the underlayment?
- How many feet of ice barrier at the eaves, and is it in every valley?
- Will all the flashing be new, including kickouts?
- Will you cut the ridge slot, and how will you keep the soffits clear?
What you can see on the day
If you're home during the job, ask to see a few things before they're covered: the ice barrier along the eave, the drip edge at the eave and rake, a valley before it's shingled, and the ridge slot before the vent goes on. Most crews don't mind a homeowner asking, and a quick photo of each is a record you'll be glad to have. Stay off the roof and out of the drop zone under the eaves; ask from the ground.
Mistakes that cut a roof's life short
- Nails driven high, above the nail line, so the shingle holds by one layer.
- An upside-down shingle used as a starter.
- A ridge vent with no slot under it.
- Old step flashing reused at a wall.
- Bath fans left venting into the attic after the new roof goes on.
If your roof is already on
You can't redo the nailing on a finished roof, but you can look for the symptoms. Shingles that slide out of place or lift in every wind usually mean high nails. A bottom course that peels back points to a missing starter. Fascia rot under a sound roof points to the drip edge. Note what you see and ask about it at your next inspection; some of it can be fixed at the edges without a full replacement.
Why it should be in writing
Every one of these belongs on the quote, because a line you can read is a line you can check. Residential roofing Madison homeowners are sold is often described as a shingle brand and a price; the roof they actually get is these details. The roof replacement page lists what a complete job includes, and the post on what replacement day looks like shows when each of them happens. If your current roof is failing young, a roof inspection will usually tell you which of these it never got.
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