Asphalt shingles remain one of the most popular roofing materials in North America because they offer a good balance of cost, durability, appearance, and ease of installation. A properly installed asphalt shingle roof can last 20 to 30 years or longer, depending on the quality of the shingles, the climate, and the care taken during installation. This comprehensive guide walks you through the complete process of installing an asphalt shingle roof, from preparation to final details.
Important safety and legal note: Roofing is dangerous work that involves heights, heavy materials, and the risk of serious injury. Always follow local contractors building codes, obtain the required permits, and strongly consider hiring a licensed professional roofing contractor. This article is for educational purposes. If you choose to do the work yourself, never work alone, use proper fall protection, and stop if weather conditions become unsafe.
Before any shingles go on the roof, careful planning is essential. Start by measuring the roof accurately. Calculate the total square footage (roofing is sold by the "square," which equals 100 square feet). Add 10 to 15 percent extra for waste, starter courses, hips, ridges, and cuts around penetrations.
Decide whether you will tear off the old roof or install over one existing layer. Most building codes allow a maximum of two layers of asphalt shingles. Installing over an existing roof saves time and money but can hide problems, add weight, and shorten the life of the new roof. A full tear-off is usually the better long-term choice.
Check the roof deck. It should be solid, dry, and free of rot or large holes. Replace any damaged plywood or OSB sheathing. The deck should be at least 1/2-inch thick plywood or 7/16-inch OSB for most residential applications. Make sure the roof has adequate ventilation. Poor ventilation is one of the main reasons asphalt shingles fail early.
Order all materials in advance and schedule the work for a period of dry weather. Ideal temperatures for installing asphalt shingles are between 40F and 85F. In very cold weather the shingles become brittle; in extreme heat they can become too soft and scuff easily.
Fall protection is non-negotiable. Use a properly fitted safety harness attached to a secure anchor point. Install roof brackets and toe boards on steep slopes. Wear soft-soled shoes with good grip, gloves, eye protection, and long pants. Keep the work area free of loose nails and debris. Never install shingles in high winds, rain, snow, or when the roof is wet or icy. Have a first-aid kit and a phone available on site.
If you are removing the old roof, start at the ridge and work downward. Use a roofing shovel to pry up the old shingles and underlayment. Remove all nails. Sweep the deck clean and inspect every sheet of plywood or OSB. Replace any soft, delaminated, or damaged sections. Drive in or remove any protruding nails. The deck must be smooth and solid before new materials go down.
Install drip edge along the eaves first. The underlayment will later cover the eave drip edge, while the rake drip edge will go on top of the underlayment.
Modern synthetic underlayment is stronger, lighter, and more tear-resistant than traditional asphalt felt. Begin by installing ice and water shield in the valleys, along the eaves (especially in cold climates), and around all penetrations. In areas with ice dam potential, run the ice and water shield from the eave up the roof to at least 24 inches inside the exterior wall line.
Roll out the underlayment horizontally, starting at the bottom of the roof. Overlap each course by at least 2 to 4 inches (follow manufacturer instructions). Secure it with cap nails or plastic-capped fasteners. Keep the underlayment smooth and free of wrinkles. At the rakes, install drip edge over the underlayment.
The starter course is critical for wind resistance and a clean edge. You can buy pre-made starter shingles or cut the tabs off regular 3-tab shingles. Install the starter course along the eaves with the sealant strip facing up and aligned near the eave edge. Overhang the drip edge by 1/4 to 3/8 inch. Nail the starter strip according to the manufacturer's pattern, usually with four nails per piece.
Snap horizontal chalk lines to keep courses straight. The first course of full shingles goes directly on top of the starter course. Offset the shingles so that the cutouts (on 3-tab shingles) or the seams (on architectural shingles) do not line up vertically from course to course. A common offset is 6 inches.
Nail placement is extremely important. Drive nails so the head is flush with the shingle surface - not under-driven or over-driven. For most architectural shingles, use four nails per shingle in normal wind zones and six nails in high-wind areas. Place nails in the designated nailing zone, usually just below the sealant strip. Never nail into the sealant strip itself.
Work from the bottom up, completing each course before moving higher. On very long roofs, you may work in sections. Keep shingles straight by following your chalk lines. Cut shingles carefully at the rakes and leave a small overhang (usually 3/8 inch) past the drip edge.
When you reach a valley, you have three common options: open metal valley, closed-cut valley, or woven valley. Open metal valleys are generally the most durable and recommended. Install the valley metal first, then cut the shingles to the proper line above the valley center.
Proper flashing prevents the majority of roof leaks. Use step flashing against walls and chimneys, weaving each piece of step flashing with the corresponding course of shingles. Counter-flashing should be embedded into the masonry or wall covering. Around plumbing vents, use rubber pipe boots sized correctly for the pipe. Apply roofing cement under the flange and nail it properly, then seal the top edge.
For skylights, chimneys, and sidewalls, follow manufacturer flashing instructions exactly. Never rely on roofing cement alone as a long-term solution.
Once the field shingles are complete, install the ridge cap. Many architectural shingle lines offer matching ridge cap shingles. Start at the bottom of a hip or at the end of the ridge opposite the prevailing wind direction. Overlap each ridge cap piece and nail on both sides, making sure nails are covered by the next piece. At the peak where hips meet the ridge, carefully cut and fit the final pieces for a clean appearance.
If you are installing a ridge vent, cut the slot in the sheathing first (before or after underlayment, depending on the system), then install the vent and cover it with ridge cap shingles designed for use over vents.
Seal any exposed nails with roofing cement. Check that all flashings are properly integrated. Walk the roof carefully and look for missing nails, crooked courses, or damaged shingles. Replace any defective pieces.
On the ground, use a magnetic nail sweeper to pick up all loose nails. Clean gutters and downspouts. Dispose of old materials and waste properly.
Even the best shingle installation will fail early without proper attic ventilation. A balanced system of intake vents (usually at the soffits) and exhaust vents (ridge vent or box vents) is required. The general rule is 1 square foot of net free ventilation area for every 150 to 300 square feet of attic floor space, depending on local code and whether a vapor barrier is present. Balanced ventilation helps prevent heat buildup in summer and moisture problems in winter.
Keep the roof free of debris, especially in valleys and gutters. Trim overhanging tree branches. Inspect the roof at least twice a year and after major storms. Look for missing, cracked, or curling shingles and address small problems before they become leaks. Avoid walking on the roof in very hot or very cold weather.
Most manufacturers offer warranties ranging from 25 years to lifetime limited warranties. These warranties usually require proper installation and may be voided by incorrect nailing, lack of ventilation, or other installation errors. Keep your receipts and any warranty registration documents.
While many experienced do-it-yourselfers successfully install asphalt shingle roofs on simple gable roofs, more complex roofs with multiple hips, valleys, dormers, or steep pitches are better left to professionals. Professionals also carry insurance, understand local code requirements, and can often obtain better material warranties. If your roof is more than one story high, has a pitch steeper than 8/12, or has complicated details, hiring a licensed roofing contractor is the safer and usually smarter choice.
Installing an asphalt shingle roof is a major home improvement project that rewards careful preparation, attention to detail, and respect for safety. By following manufacturer instructions, using quality materials, installing proper underlayment and flashing, and ensuring good attic ventilation, you can achieve a durable, attractive roof that protects your home for decades. Whether you do the work yourself or hire a professional, understanding the complete process helps you make informed decisions and recognize quality workmanship.
Take your time, prioritize safety, and do each step correctly the first time. A well-installed asphalt shingle roof is one of the best investments you can make in your home.