How to Install Asphalt Shingles: Step-by-Step Guide

Watching a roofing crew tear off and replace shingles in a weekend makes asphalt shingles roof installation look simple. It isn't. Get the underlayment overlap wrong, misalign a single course, or skip the drip edge, and you'll have leaks finding their way into your attic within a year or two, no matter how good the shingles look from the street.

This guide walks through the actual shingle roof installation steps professionals follow, from tearing off old material and checking the decking to laying starter strips, running courses, and flashing valleys and penetrations correctly. You'll get the specific nail placement, exposure measurements, and sequencing that separate a roof that lasts 25 years from one that fails at year five.

We wrote this because homeowners across Kirkland, Bothell, and the greater Seattle area keep asking us the same questions before tackling roof shingle installation themselves. Washington's wet climate punishes shortcuts, so we're covering material selection, prep work, and technique in the order you'll actually use them, whether you're doing this yourself or just want to know what a quality job should look like before you sign off on one.

What you need before installing asphalt shingles

Before you touch a single shingle, gather everything you need and confirm your roof actually qualifies for a straightforward tear-off. A shingle roof installation that starts with the wrong materials or an unpermitted plan turns into a costly redo, so treat this planning stage as seriously as the work itself.

Materials list

Buy roughly 10% more shingles than your calculated square footage to cover waste from cuts, valleys, and hips. Here's what a typical mid-size roof (2,000 to 2,400 square feet) requires:

Material	Quantity (approx.)	Notes
Architectural asphalt shingles	22-24 squares	1 square covers 100 sq ft
Synthetic underlayment	22-24 squares	Skip 15lb felt; synthetic resists tearing
Ice and water shield	3-4 rolls	Required at eaves and valleys in WA
Drip edge (aluminum)	200-250 linear ft	Matches perimeter length
Starter strip shingles	200-250 linear ft	Or cut from full shingles
Ridge cap shingles	4-6 bundles	Sized for hip and ridge length
Roofing nails (1.25")	30-35 lbs	Galvanized, hot-dipped preferred
Roofing cement/sealant	3-4 tubes	For flashing and repairs
Step and valley flashing	As needed	Aluminum, 26-gauge minimum

A roof is only as good as its weakest layer, and that's almost never the shingles you can see.

Tools you'll need

Skipping the right tools costs you time and precision. Get these before you climb up:

• Pneumatic roofing nailer (or hammer for smaller jobs)

• Utility knife with hook blades for shingle cuts

• Chalk line for course alignment

• Tin snips for flashing

• Pry bar and roofing shovel for tear-off

• Tarps to protect landscaping and gutters

• Harness and roof brackets for safety on slopes over 6/12

Checking your roof deck condition

Good shingles over rotten decking is a wasted investment. Walk the attic first and look for daylight through the sheathing, soft spots, or water stains that trace back to specific rafters. Press on the deck from below with a flashlight at night; any give under hand pressure means that section needs replacing before you go further.

Once you're on the roof itself, check for spongy areas underfoot, delaminated plywood edges, or sheathing thinner than 7/16 inch, which doesn't meet most current building codes. Replace bad sections with matching thickness OSB or plywood, and refasten the whole deck with ring-shank nails on 6-inch centers along edges and 12-inch centers in the field.

Permits matter more than most DIYers expect. Kirkland and most surrounding municipalities require a roofing permit for full asphalt shingle roof installation jobs, and skipping this step can complicate insurance claims later if something goes wrong. Check with your local building department before ordering materials, since inspection requirements sometimes dictate underlayment type or nailing patterns you'll want to plan around from day one.

Step 1. Prepare the roof deck and install drip edge

Strip the old roofing down to bare decking before you install anything new. Layering new shingles over old ones traps heat, hides deck damage, and voids most manufacturer warranties, so a proper asphalt roof shingles installation always starts with a clean deck.

Tear off and inspect

Work in sections so you're never leaving a large area exposed to Seattle's unpredictable weather overnight. Pull old shingles, felt, and nails with a roofing shovel, then sweep the deck clean and pull any remaining fasteners by hand. Check every sheet of sheathing for soft spots, delamination, or gaps wider than 1/8 inch, and swap bad sections for matching-thickness plywood or OSB before moving forward.

Fasten and flatten the deck

Re-nail the entire deck surface even where it looks solid. Loose sheathing squeaks under foot traffic and eventually works nail heads loose beneath the shingles, which shows up as leaks years later.

• Use ring-shank nails, not smooth shank

• Space nails 6 inches apart along panel edges

• Space nails 12 inches apart in the field

• Sink nail heads flush, never below the surface

A shingle roof is only as flat and secure as the deck underneath it.

Install the drip edge

Run drip edge along the eaves first, before any underlayment goes down. This directs runoff away from the fascia and into the gutter instead of behind it, which is one of the most common failure points we see on older homes around Bothell and Kenmore. Nail it every 12 inches with 1-inch galvanized nails, overlapping each piece by 2 inches. Save the rake edge drip edge for after underlayment installation, since the sequence differs there. Getting this order right during installation roof shingles work prevents the wood rot that shows up years later along roof edges.

Step 2. Install ice and water shield and underlayment

With the drip edge in place at the eaves, move straight to your water-resistant barrier before any weather sneaks in overnight. This layer does the real waterproofing work, and skipping or shortcutting it is where most shingles roof installation failures start, even on jobs where the visible shingle work looks flawless.

Lay the ice and water shield first

Roll ice and water shield along the eaves, extending it at least 24 inches past the interior wall line, which covers most homes in the Kirkland and Bellevue area given our roof pitches and attic insulation depths. Peel the backing as you go and press firmly, working from the edge upward so water always flows over seams, never into them. Run the same membrane through every valley, extending 18 inches up each side from the centerline, since valleys concentrate more runoff than any other part of the roof.

Skip the ice and water shield at your own risk. It's the one layer that catches what everything else misses.

Roll out synthetic underlayment

Start at the eave and work toward the ridge, overlapping each horizontal course by at least 4 inches and each vertical seam by 6 inches. Synthetic underlayment holds up better than old-school felt against Washington's rain and wind, and it won't tear underfoot the way 15lb felt does on a wet morning. Fasten with cap nails spaced 12 inches apart in the field and 6 inches along seams.

• Cover the entire deck before cutting any openings for vents or skylights

• Trim excess at the ridge once both roof planes are covered

• Keep courses straight using a chalk line every few rows

Finish the rake edge drip edge

Once the underlayment covers the deck, install drip edge along the rakes, overlapping it over the underlayment rather than under it. This sequence matters: eave drip edge goes under the underlayment, rake drip edge goes over it. Getting this backward is a common mistake in DIY asphalt shingle roof installation projects, and it lets wind-driven rain sneak behind the metal instead of running off it.

Step 3. Flash the valleys, walls, and roof penetrations

Flashing is where most leaks actually start, not in the open field of shingles. Every place your roof meets a wall, chimney, pipe, or another roof plane needs metal that directs water away from the seam, and getting this wrong during shingle roof installation steps undoes all the careful underlayment work you just finished.

Valley flashing

For open valleys, run 24-gauge galvanized W-valley metal centered over the ice and water shield, overlapping sections by at least 6 inches with the upper piece lapping over the lower one. Nail only at the outer edges, roughly 1 inch from each side, and never through the center where water concentrates. If you're using a closed-cut valley instead, run shingles from one side across the valley first, then trim the overlapping side 2 inches back from the centerline and seal the cut edge with roofing cement.

Wall and chimney flashing

Wherever a roof plane meets a sidewall or chimney, install step flashing, one piece per shingle course, each piece overlapping the one below by at least 2 inches. Nail the flashing to the deck only, never through the wall siding, and let the siding or counter-flashing above cover the top edge. Skipping step flashing in favor of a single continuous piece is a shortcut that fails within a few years, especially in the wet cycles the Puget Sound area sees every winter.

Flashing failures cause more roof leaks than worn-out shingles ever do.

Pipe boots and vent flashing

Slide rubber or lead pipe boots over vent stacks before shingles run past them, sealing the base with roofing cement and nailing the flange corners. Set metal vent flashing the same way, tucking the top edge under the upper course of underlayment and letting shingles overlap the sides and bottom. Check every boot and flange for gaps before you cover them, since these small penetrations account for a disproportionate share of the leak calls we get around Redmond and Woodinville each spring.

Step 4. Install starter strips, field shingles, and ridge caps

With flashing done, you're ready for the visible layer that actually sheds water for the next two decades. This is the part most homeowners picture when they think of shingle roof installation, but the sequence and nail placement matter just as much here as anywhere else in the job.

Lay the starter strip

Run starter strip shingles along the eave first, adhesive side facing up toward the roof, overhanging the drip edge by 3/8 to 1/2 inch on both the eave and rake edges. This seals the first course of field shingles against wind lift and blocks water from creeping under the tabs. Nail the starter strip 3 to 4 inches up from the eave, spacing fasteners every 12 inches.

Skip the starter strip and you've built a wind-uplift problem into the very first course.

Run your field shingles

Start your first course flush with the starter strip, then offset each subsequent course so the cutouts never align vertically, typically a 6-inch offset for standard three-tab or a random stagger pattern for architectural shingles. Drive four nails per shingle, 1 inch above the tab slots and roughly 1 inch in from each end, adding a fifth nail in high-wind zones common around Bellevue's exposed ridgelines. Keep exposure consistent, usually 5 inches for standard shingles, and snap a chalk line every few courses to catch drift before it compounds.

• Nail placement: 4 nails standard, 6 nails in high-wind areas

• Exposure: check manufacturer spec, typically 5 inches

• Offset cutouts: 6 inches minimum between courses

Cap the ridges and hips

Once both roof planes meet at the ridge, cut individual ridge cap shingles from a bundle or use pre-cut caps, and nail each one 1 inch from each edge with two nails per cap. Overlap caps to shed water downhill in the direction of prevailing wind, working from the bottom of hips toward the ridge, then finish the ridge itself from one end to the other.

Knowing when to call in a professional

Every step in this guide is doable if you're comfortable on a ladder, careful with measurements, and willing to spend a few weekends on the roof. But asphalt shingles roof installation punishes mistakes you won't spot until water shows up on your ceiling, and by then the fix costs far more than the shingles did. Steep pitches, complicated valleys, multiple penetrations, or decking that's already showing rot are the moments to stop and call in a crew that does this every week, not every few years.

Legacy Exteriors LLC has handled roof shingles installation for homeowners across Kirkland, Bothell, Woodinville, and the greater Seattle area, and we back every job with a locked-in price quote, so you know the cost before we start. If your roof needs more than a patch, or you'd rather have it done right the first time, request your free quote and inspection and we'll walk the deck with you before anything gets torn off.