9.2 Installing Asphalt Shingles: Starter, Exposure, Nailing, Steep Slopes & Caps
Key Takeaways
Shingle nails must be galvanized steel, stainless steel, aluminum, or copper, with at least a 12-gauge (0.105-inch) shank and a 3/8-inch head, meeting ASTM F1667.
Nails must penetrate at least 3/4 inch into the sheathing, or completely through sheathing thinner than 3/4 inch.
Each strip shingle needs at least 4 fasteners, or 2 per individual shingle, and more where the manufacturer requires. Above 21:12, follow the manufacturer's steep-slope method.
Nails placed above the manufacturer's nail line (high nailing) can miss the underlying course and reduce wind resistance, and overdriven nails cut into the shingle.
The starter course places sealant near the eave so the first course seals down, and shingles typically overhang the drip edge by the small distance the manufacturer specifies.
Before the First Shingle
Check that the deck is solid and fastened (Section 8.1). Then check the installation sequence: drip edge at the eaves, ice barrier over it (reaching 24 inches inside the wall line), underlayment or double underlayment by slope, drip edge over the underlayment at the rakes, and valley linings in place. Snap horizontal chalk lines for courses and vertical lines for offsets.
Code Minimums
| Requirement | 2015 MRC |
|---|---|
| Deck | Solidly sheathed (R905.2.1) |
| Slope | 2:12 or greater. Double underlayment from 2:12 to less than 4:12 (R905.2.2) |
| Fastener material | Galvanized steel, stainless steel, aluminum, or copper roofing nails (R905.2.5) |
| Fastener size | Shank at least 12 gauge (0.105 in), head at least 3/8 in, meeting ASTM F1667 |
| Penetration | Through the roofing and at least 3/4 in into the sheathing. Where sheathing is thinner than 3/4 in, through the sheathing |
| Number | At least the manufacturer's number, and never fewer than 4 per strip shingle or 2 per individual shingle (R905.2.6) |
| Very steep slopes | Above 21:12 (175% slope), install as the manufacturer requires |
| Ice barrier | Where required (all Michigan homes), per R905.1.2 (R905.2.7) |
The code calls for nails, not staples. On a reroof over an existing layer, where a recover is allowed, use nails long enough to reach the required penetration.
Starter Course
The starter course fills the spaces under the first course's cutouts and joints, and it puts sealant at the eave so the first course bonds down. Use the manufacturer's starter product, or cut starter from field shingles the way the instructions describe. The usual approach removes the tabs and places the sealant strip up and near the eave edge. Offset starter joints from the first course's joints. Many manufacturers also call for starter along the rakes to improve wind resistance.
Overhang: Shingles typically overhang the drip edge at eaves and rakes by a small amount, commonly about 1/4 to 3/4 inch, as the manufacturer specifies. Too little lets water wick back. Too much lets the edge sag and catch wind.
Exposure, Offsets, and Alignment
- Exposure is the part of each course left exposed to weather. English 3-tab shingles are about 5 inches, and metric laminated shingles about 5 5/8 inches. Use the exposure printed on the wrapper.
- Offsets keep joints from lining up course over course, which would create a leak path. Follow the manufacturer's stagger pattern and minimum offset, often at least 4 to 6 inches between adjacent courses.
- Alignment: snap lines at intervals to keep courses parallel to the eave and ridge. Don't mix shingles from different manufacturers or sizes on the same roof plane.
Nail Placement and Driving
The manufacturer marks a nail line or nailing zone. On laminated shingles, nails in the zone pass through both layers of the shingle and through the top of the course below.
| Error | Result |
|---|---|
| High nailing (above the zone) | Can miss the course below and reduce pull-through and wind resistance. A common cause of blow-offs and voided warranties |
| Overdriven | The head cuts into the mat, and holding power drops |
| Underdriven | The raised head can puncture the shingle above or prevent sealing |
| Angled | Part of the head cuts in and part stands up |
| Too few nails | Below the code or manufacturer minimum |
Set the pneumatic nailer's depth so heads sit flush with the shingle surface. In cold weather, check depth often, because stiffer shingles and colder air pressure change the result.
High-Wind and Steep-Slope Application
Manufacturers publish enhanced nailing (often 6 nails per shingle) for high-wind areas or enhanced warranties, and steep-slope instructions for mansards and slopes above about 21:12. Steep-slope instructions typically call for more nails plus hand-sealing each shingle with spots of asphalt roofing cement. The code defers to the manufacturer above 21:12, and its instructions are enforceable because R905.1 requires following them. Use only a small amount of cement, because too much can blister or bleed.
Cold-Weather Sealing
Sealant strips need warmth and sun. Shingles installed in late fall may not seal until spring. Many manufacturers require hand-sealing below a stated temperature or in windy exposures. Handle cold shingles carefully, because they crack when bent.
Hips and Ridges
- Use the manufacturer's hip and ridge cap shingles, or cap cut as instructed from 3-tab shingles. Laminated field shingles are generally not suitable for caps.
- Apply caps starting at the bottom of each hip, and on the ridge from the end away from the prevailing wind, with the exposure and nail length the manufacturer specifies.
- With a ridge vent, install the vent over the slot per its instructions, then cap over the vent with longer nails (Section 12.2).
Flashing Tie-In
Base and cap flashing for shingles is corrosion-resistant metal at least 0.019 inch thick (base flashing may also be mineral-surfaced roll roofing of at least 77 pounds per 100 square feet), installed per the manufacturer (R905.2.8.1). Sidewalls use step or continuous base flashing at least 4 by 4 inches (R905.2.8.3). Vent pipes, front walls, and chimneys follow the shingle manufacturer's printed instructions (R905.2.8.4). Chapter 11 covers these details.
Final Inspection Checklist
Check straight courses and proper offsets, no exposed nails except where the instructions allow, correct overhangs, sealed tabs or hand-sealing where needed, clean valleys, secure flashings, open vents, and a magnetic sweep of the grounds.
What minimum fastener does the 2015 MRC require for asphalt shingles?
A corrosion-resistant roofing nail with at least a 12-gauge (0.105-inch) shank and a 3/8-inch head, meeting ASTM F1667
A 16-gauge staple with a 7/16-inch crown
An 8d common nail with a 1/4-inch head
Any nail that reaches the deck
Shingles are being nailed through 7/16-inch OSB. What penetration does R905.2.5 require?
At least 3/4 inch into the OSB, stopping short of the underside
Through the sheathing, because it is thinner than 3/4 inch
At least 1/2 inch into the OSB
Any penetration that holds the shingle
A crew is installing laminated shingles on a 24:12 mansard face. Whose instructions govern the fastening method under the 2015 MRC?
The shingle manufacturer's, because R905.2.6 requires installation as the manufacturer requires above 21:12
The building official's, because the code sets no steep-slope rule
None, because asphalt shingles are prohibited above 21:12
The standard 4-nail pattern with no additional steps
Sections you finish are checked off in the contents.