Introduction: Why Composition Roofing Is the Top Choice for Garages
Composition asphalt shingles remain the most popular roofing material for residential garages across North America, offering affordability, ease of installation, proven durability spanning 20-30 years, and broad aesthetic versatility. A typical two-car garage roof represents approximately 600-800 square feet, making it an ideal DIY project or straightforward professional job. Material costs range from $500 to $1,500 for a standard garage, with professional installation adding $700 to $2,000.
This guide covers everything from material selection and code compliance through underlayment, shingle application, flashing, and ventilation.
Understanding Composition Roofing Materials
Modern composition shingles consist of a fiberglass or organic felt mat coated with asphalt and surfaced with ceramic-coated mineral granules. Fiberglass mat shingles offer superior fire resistance (Class A versus Class C). The two primary categories are three-tab shingles (flat, uniform appearance) and architectural shingles (multi-layer, textured appearance with deep shadow lines). Architectural shingles carry wind warranties of 110-130 mph versus 60 mph for three-tab, making them preferable in high-wind areas.
| Shingle Type | Weight/Sq | Wind Rating | Warranty | Cost/Sq |
|---|---|---|---|---|
| Three-tab fiberglass | 200-235 lbs | 60 mph | 20-25 years | $80-110 |
| Architectural | 240-350 lbs | 110-130 mph | 25-30 years | $100-150 |
| Premium/luxury | 350-480 lbs | 130+ mph | 30-50 years | $180-300 |
Tools and Materials
Essential tools: roofing hatchet or pneumatic nail gun, utility knife with hook blades, chalk line, measuring tape, ladder with stabilizer, roofing shovel, magnetic sweeper. For a single-car garage (12×22 ft, 4:12 pitch): 6-7 squares of shingles, 1 roll #15 or #30 felt underlayment, 1 box 1-1/4 inch galvanized roofing nails, drip edge metal, ridge cap shingles or ridge vent material.
Step-by-Step Installation
Deck Preparation and Underlayment
The deck must be clean, dry, and structurally sound. Per IRC R803, minimum deck thickness is 7/16-inch OSB or 1/2-inch plywood for rafters 24 inches on center. Install drip edge at eaves, then apply #15 felt horizontally with 2-inch horizontal and 4-inch vertical overlaps. For slopes 2:12 to 4:12, two layers of underlayment are required per IRC R905.2.7.
Ice and Water Shield
In IECC climate zones 5 and above, install ice and water shield extending at least 24 inches past the interior wall line at eaves per IRC R905.2.7.1.
Starter Strip and Courses
Install starter strip overhanging the drip edge by 1/4-3/8 inch. Snap a chalk line 6 inches up from eave. Install shingles with four nails each. Offset subsequent courses by half a tab (6 inches). Maintain consistent exposure (5 inches for three-tab).
Valley and Flashing Details
Install 36-inch-wide ice and water shield in valleys. Use 24-inch wide valley flashing. For open valleys, trim shingles 2-3 inches back from centerline. At sidewalls, install step flashing integrated with each course, covered by counter-flashing.
Ventilation and Ridge Cap
IRC requires minimum 1:300 vent area with vapor retarder, or 1:150 without. Ridge vents with soffit vents provide the best system. Install ridge cap shingles with 5-inch overlap.
Resources
Learn about roof ventilation systems Read about roofing underlayment Explore cool roof systems See ice and water shield installation