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Asphalt shingle installation succeeds when the entire roof assembly sheds water and every shingle is attached in the location and pattern its manufacturer specifies. Start by checking the roof deck, slope, weather, local code and the selected product’s current instructions—not by copying a nail pattern from a different bundle. The sequence generally runs from deck preparation to water barrier, underlayment, drip edge, starter strips, flashing, shingle courses, hip and ridge details, and final inspection. Small errors in laps, flashing or fastener placement can allow leaks or reduce wind resistance, so treat the instructions for your exact shingle and the locally adopted code as controlling.
What should you check before installing asphalt shingles?
Confirm four things before materials cover the deck: the deck is sound, the roof slope is allowed for the product, the weather is suitable, and local requirements are understood. A roof that looks ready from the ground may have rotten sheathing, inadequate support, old flashing or a slope outside the shingle’s approved range.
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- Deck: It should be adequately supported, dry and free of damaged or loose panels. Replace deteriorated sheathing and correct protruding fasteners before underlayment goes down. Product instructions may specify minimum deck materials; follow those requirements rather than assuming any wood surface qualifies. The Duration installation instructions are an example of product-specific deck requirements.
- Slope: Measure roof pitch as rise over a 12-inch horizontal run. A 4:12 roof rises 4 inches for every 12 inches of run. Some shingles are not approved below 2:12. For example, the IKO Cambridge technical sheet says not to apply that product below 2:12 and gives special requirements for slopes from 2:12 to under 4:12.
- Code and climate: Check the building department’s adopted code, including amendments for ice, wind, fire and ventilation. The 2024 International Residential Code is a model code; your jurisdiction may use an earlier edition or local modifications. See IRC Chapter 9 for the model-code baseline.
- Weather and access: Plan for dry conditions, secure material storage and safe roof access. Do not work on wet, icy or wind-exposed slopes. A sloped roof requires appropriate fall protection and personal protective equipment; the Cambridge technical sheet cautions that work at height can be dangerous.
Read the complete, current shingle instructions before opening bundles. Keep the instructions on site so installers can verify exposure, offsets, nail zones, approved accessories and special weather details as work progresses.
Do asphalt shingles need underlayment?
Yes. Underlayment is part of the roof’s water-control system, but its type, placement and laps depend on slope, climate, code and product approval. It is not a substitute for correctly integrated flashing or a watertight shingle layout.
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At standard slopes, manufacturers commonly specify a synthetic or other approved underlayment over the deck. Low-slope roofs need more substantial protection. For its Duration products, the manufacturer describes one underlayment approach at 4:12 and steeper and two alternative approaches from 2:12 to under 4:12. Those details are not universal; use the exact instructions for your product and the underlayment manufacturer’s directions.
Where local conditions require it, install an approved ice-and-water barrier at eaves, valleys, sidewalls or other vulnerable areas. Confirm its width, laps and termination points with local code and the product instructions. Keep the deck clean and dry, roll out underlayment without wrinkles, and fasten it so wind cannot lift it before shingles are applied. Do not leave exposed underlayment longer than the manufacturer allows.
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What is the correct order for drip edge, starter strips and flashing?
These parts must be integrated, not added as cosmetic trim after shingles are laid. A typical sequence is eave-edge preparation, underlayment and drip-edge integration, then starter strips, with wall, valley and penetration flashing installed so each upper layer sheds onto the layer below. Exact sequencing can change at rakes, valleys and wall intersections.
Drip edge
Install the specified metal drip edge along eaves and rakes, with joints overlapped as directed. It should direct runoff clear of the fascia and protect the deck edge. Coordinate the metal with underlayment and starter strips so water cannot run behind the edge. Local code or the shingle instructions may require different placement at eaves versus rakes.
Starter strips
Starter shingles provide the first sealing line and establish the eave overhang. A general Building America detail places the adhesive toward the overlying shingle, extends the starter about 1/4 to 3/4 inch beyond the eave edge, and places nails roughly 2 to 3 inches from that edge. These are guide dimensions, not a universal specification; use the starter product’s instructions for cut lines, overhang and nail locations. The PNNL asphalt-shingle guide explains how starter strips, drip edge and flashing work together.
Flashing
Install step flashing at sidewalls, headwall flashing where a roof meets an upper wall, and properly approved flashing around chimneys, skylights, vents and plumbing penetrations. Each shingle course should overlap the flashing in the prescribed direction. Never bury a required flashing piece under a later component that should have been installed first, and never rely on exposed sealant as the primary water barrier.
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Begin at the eave and work upward, using the manufacturer’s exposure, course offset and alignment marks. Keep courses straight and maintain the specified overhang at eaves and rakes.
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- Snap control lines. Establish an eave reference and vertical alignment lines. Use the product’s layout diagram to prevent cumulative drift as courses rise.
- Lay the first course over the starter. Position shingles so the starter’s adhesive strip seals the underside of the first exposed course. Follow the required side and eave overhang.
- Offset each succeeding course. Interlock or stagger joints by the specified amount. For example, the Duration directions use a 6 1/2-inch offset and 5 5/8-inch exposure for that product family. Do not transfer those figures to another shingle line.
- Maintain minimum offsets. Manufacturer diagrams may require different offsets between particular courses to keep joints from lining up. Reject damaged tabs and do not force a shingle into a distorted position.
- Integrate obstacles as you go. At walls, valleys and penetrations, weave or cut shingles around flashing exactly as shown in the instructions. Keep the water-shedding direction continuous.
Use only approved shingles and accessories together. Mixing profiles, starter products or ridge components can change sealing and warranty conditions.
How many nails do you use per shingle?
Use the number, nail type, length, corrosion resistance and placement zone specified for the exact product and exposure. As a model-code baseline, the 2024 IRC states at least four fasteners per strip shingle or two per individual shingle, subject to approved manufacturer instructions and local adoption. A manufacturer can require more.
| Situation | Published requirement or example | How to apply it |
|---|---|---|
| Model-code baseline | At least four fasteners per strip shingle or two per individual shingle in the 2024 IRC | Verify your jurisdiction’s adopted text and the product approval; the code baseline does not override stricter instructions. |
| Standard Cambridge application | IKO technical data lists four nails for standard application | Use the marked nail line and the nail specifications in the current Cambridge sheet. |
| Steep Cambridge application | IKO lists six nails for steep-slope applications | Confirm the slope threshold and all other steep-slope details in the product sheet. |
| Duration on slopes over 60 degrees (21 inches per foot) | Six fasteners plus four spots of asphalt roof cement per shingle | Use cement only where the instructions require it; excessive cement can blister shingles. |
Place nails in the marked or specified nailing zone, not merely at an even-looking spacing. Nails should be straight and flush with the shingle surface: not tilted, high, low, overdriven or underdriven. An overdriven head can cut through the mat; an underdriven head can hold the next course up and leave a leak path. If using a pneumatic nailer, adjust pressure and depth on scrap material before fastening production shingles, then check the first installed courses.
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Can you install shingles on a low-slope roof?
Only when the selected product is approved for that slope and the low-slope underlayment and flashing system is installed exactly as required. A roof from 2:12 to below 4:12 cannot be treated like a conventional 4:12 roof because water moves more slowly and laps are more vulnerable.
Check the product’s minimum slope first. Cambridge, for example, is not to be applied below 2:12, and its technical sheet calls for special treatment in the 2:12-to-under-4:12 range. The Duration instructions likewise specify different underlayment options for that range. If the roof is below the approved minimum, choose a roofing system rated for the slope rather than attempting to modify asphalt shingles with extra sealant.
Low-slope work also magnifies errors at valleys, sidewalls, penetrations and eaves. Plan positive drainage, verify every lap and consider a qualified roofing professional when the roof geometry is complex or access is unsafe.
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What changes in cold weather or on a steep roof?
Factory-applied sealant may not activate immediately in cool conditions, and steep roofs increase both sliding and wind forces. Follow the temperature, hand-sealing and storage directions for the product; do not assume sunlight alone will correct a poorly placed shingle.
For steep slopes, the Duration instructions require six fasteners and four spots of asphalt roof cement per shingle above 60 degrees or 21 inches per foot. Apply only the specified amount and locations. Too much cement can blister shingles, trap heat or create an uneven surface. Use roof brackets, ladders and fall-arrest equipment appropriate to the slope, and stop when wind or surface conditions make footing unreliable.
How should ridge, hip and ventilation details be finished?
Complete hips and ridges with the approved cap shingles or ridge product, using the specified exposure, fasteners and direction. End laps and final caps must shed water away from prevailing exposure and be secured against wind.
Ventilation must comply with local building code and the shingle manufacturer’s requirements. Do not block soffit intake with insulation or underlayment, and do not add a ridge vent without confirming that intake and exhaust paths are balanced. Both the Duration instructions and IKO guidance direct installers to follow local ventilation requirements; no single vent arrangement fits every roof.
What should you inspect before calling the roof complete?
Walk the roof only with safe access and fall protection, or inspect from ladders and ground where conditions are hazardous. Compare the finished work with the product diagrams and code requirements.
- Look for missed, misplaced, tilted, high or overdriven fasteners.
- Check that no nail heads are exposed where they should be covered.
- Verify straight courses, correct exposure, offsets and eave/rake overhangs.
- Confirm starter strips are continuous and adhesive faces the overlying shingle.
- Inspect drip-edge laps and the transitions between metal, underlayment and shingles.
- Check step, headwall, valley and penetration flashing for correct overlaps and visible gaps.
- Replace cracked, creased or torn shingles rather than sealing over damage.
- Ensure ridge caps, vents and pipe flashings are fully fastened and sealed as specified.
- Clear loose nails and debris from valleys, gutters and the ground.
Photograph concealed flashing and underlayment before they are covered. Keep bundle labels, invoices and the installation instructions with the property records; they can help with future repairs, inspections and warranty questions.
What are the most common asphalt-shingle installation mistakes?
Copying another product’s layout
Exposure, offsets, nail zones and steep-slope rules vary. A pattern that is correct for one line can be wrong for another. Use the exact current instructions.
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Driving nails outside the zone
Nails placed too high may miss the intended reinforcement; nails too low can be exposed or interfere with the next course. Refasten according to the manufacturer’s repair direction instead of simply adding random nails.
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Ignoring low-slope requirements
Installing standard underlayment and ordinary laps on a 2:12-to-under-4:12 roof can leave the assembly vulnerable to water migration. Confirm the slope before ordering materials.
Skipping starter, drip edge or flashing integration
These components control water at the roof perimeter and interruptions. Omitting them creates a failure path that surface sealant rarely fixes permanently.
Using too much cement
More asphalt cement is not automatically better. Where a product requires cement, apply the specified spots and quantity; the Duration instructions warn that excess can blister shingles.
Working without fall protection
A roof can be unsafe even when it is dry and appears shallow from the ground. Use appropriate protection or hire a qualified contractor for steep, high or difficult-to-access work.
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When should you hire a roofing contractor?
Professional help is the prudent choice when the deck may be damaged, the roof has multiple valleys or wall intersections, the slope is steep or low, code requirements are uncertain, or safe fall protection is not available. A contractor can verify concealed flashing, coordinate permits and document the installation. Ask for the exact shingle and accessory instructions, the proposed nail pattern, underlayment approach and details for penetrations before work begins.
For a straightforward roof, an experienced installer should still be able to explain why the chosen product is allowed on the measured slope and how the assembly meets local requirements. If an estimate relies on a generic “six nails everywhere” or “seal it with cement” rule without identifying the product, request clarification before signing.
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What materials and tools are typically needed?
The shopping list depends on the roof and product, but commonly includes approved asphalt shingles, matching starter strips and ridge caps, roofing nails, underlayment, any required ice-and-water barrier, drip-edge metal, step or other flashing, pipe boots and ventilation components. A chalk line, tape measure, utility knife, straightedge, roofing hammer or adjusted pneumatic nailer, snips and ladders are typical tools. Choose every accessory for compatibility with the shingle, deck, slope and local code; availability or a low price does not make an unapproved component suitable.
Store bundles flat or as directed, protect them from moisture and avoid stacking them where the deck cannot support the load. Do not bend shingles sharply in cold weather, and follow the manufacturer’s handling limits.
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Code is the legal minimum adopted by your jurisdiction; the manufacturer’s instructions are part of the product’s approved installation and may be more specific or more demanding. Where they differ, ask the building official or manufacturer for a documented resolution before installation. Keep the jurisdiction, product name, series, revision date and roof slope in the project file so the requirements can be checked later.
The Oakridge and Duration instructions, the Cambridge technical sheet and the PNNL roof guide illustrate why a single universal recipe is unsafe. Use them as references for the named products and principles, not as permission to apply their dimensions to every asphalt shingle.
Frequently Asked Questions
How long should asphalt shingles last after proper installation?
The sources for this guide do not establish a universal service life, and lifespan varies with product class, climate, ventilation, maintenance and exposure. Use the selected manufacturer’s warranty and published product documentation for its stated coverage, while treating installation compliance as a condition of that coverage.
Can I put new asphalt shingles over an existing layer?
Whether a re-cover is allowed depends on local code, the number and condition of existing layers, deck condition and the new product’s instructions. An inspection is needed to find hidden rot, uneven surfaces and failed flashing; removing the old roof is often necessary when those conditions cannot be verified.
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Nail length must provide the penetration required by the shingle instructions and the deck assembly, which varies with sheathing thickness and any existing roofing. Select the length from the product documentation and local code rather than from a generic roofing-nail chart.
Should valleys use an open-metal or closed-cut design?
The approved valley method depends on the shingle system, climate, slope and local requirements. Follow the product’s valley detail and flashing instructions; changing the method can alter water flow and may affect approval or warranty conditions.
