Roofing Installation

The roof is the single most important weather barrier on any building. A properly installed roof keeps water out for decades. A poorly installed one leaks within months and can cause tens of thousands of dollars in damage to the structure below. Roofing work demands both precision and safety awareness - it is consistently one of the most hazardous construction trades due to the combination of working at height, carrying heavy materials, and operating power tools on angled surfaces. This comprehensive guide covers asphalt shingle roofing (the most common residential system), along with essential information on other roofing systems, flashing details, ventilation, and the safety protocols that keep you alive on the roof.

Roof Anatomy

Before installing any roofing material, understand the structure and terminology:

Structural Components

• Rafters - Angled structural members that support the roof deck. Sized by span and load (typically 2x8 to 2x12 for residential).
• Trusses - Prefabricated triangular frames that replace individual rafters on most modern construction. Engineered for specific loads and spans.
• Ridge board/beam - The horizontal member at the peak where rafters meet
• Collar ties and rafter ties - Horizontal members that prevent the roof from spreading
• Roof deck (sheathing) - Plywood or OSB panels (typically 7/16-inch or 1/2-inch OSB, or 1/2-inch plywood) nailed to the rafters. This is the substrate for all roofing materials.

Roofing Components (Bottom to Top)

• Drip edge - L-shaped metal flashing along the eaves and rakes that directs water into the gutter and away from the fascia board
• Ice and water shield - Self-adhering rubberized membrane applied at the eaves, valleys, and around penetrations. Required by code in cold climates.
• Underlayment - Water-resistant layer over the entire deck
• Starter strip - The first course of shingles along the eave, providing a seal line under the first full-course shingle tabs
• Field shingles - The main roof covering
• Hip and ridge cap - Specially shaped or cut shingles that cover the hips and ridge
• Flashing - Metal or membrane installed at every roof transition: walls, valleys, penetrations, chimneys

Roof Geometry Terms

• Eave - The lower edge of the roof that overhangs the wall
• Rake - The sloped edge of the roof at the gable end
• Ridge - The peak where two slopes meet
• Hip - The angled ridge where two roof slopes meet at an outside corner
• Valley - The channel where two roof slopes meet at an inside corner
• Dormer - A structure that projects from the roof slope, adding a window
• Slope (pitch) - Expressed as rise over run. A 6:12 roof rises 6 inches for every 12 inches of horizontal run. Most shingles require a minimum 4:12 slope (lower slopes need special installation methods or different roofing systems).

Materials Specifications

Asphalt Shingles

Asphalt shingles account for roughly 80% of the residential roofing market:

• Three-tab shingles - Single-layer shingles with three tabs cut into the lower portion. Lightest weight, lowest cost, shortest warranty (20-25 years). Installed with 5-inch exposure (5 inches of each shingle visible).
• Architectural (dimensional/laminate) shingles - Multi-layer shingles that create a three-dimensional appearance. Heavier, more wind-resistant, longer warranty (30-50 years, lifetime on premium grades). Standard exposure is 5-5/8 inches. This is the current industry standard.
• Premium/designer shingles - Thick, heavy shingles that mimic slate, cedar shake, or tile. Top warranties. Significantly heavier per square.
• Weight per square - A "square" covers 100 square feet of roof area. Three-tab: 200-240 lbs/square. Architectural: 250-350 lbs/square. Premium: 350-450 lbs/square.
• Wind ratings - Standard: 60-70 mph. High-wind: 110-130 mph. Some premium shingles are rated to 150 mph with enhanced nailing.

Underlayment

• 15-lb asphalt-saturated felt (tar paper) - Traditional underlayment. Minimum overlap: 2 inches on horizontal laps, 4 inches on end laps. Adequate for most applications but tears easily and wrinkles when wet.
• 30-lb felt - Heavier, more tear-resistant than 15-lb. Required on slopes below 4:12 (double layer).
• Synthetic underlayment - Woven polypropylene. Lighter, stronger, more tear-resistant, and lays flatter than felt. Does not wrinkle when wet. Most manufacturers require synthetic underlayment for warranty compliance on premium shingles.

Ice and Water Shield

• Self-adhering rubberized asphalt membrane that seals around nail penetrations
• Required by IRC (International Residential Code) in areas where the mean daily January temperature is 25 degrees F or less
• Install at eaves extending at least 24 inches past the interior wall line (typically 3-6 feet from the eave edge)
• Also install in all valleys, around chimneys, at skylights, and at other penetrations
• Application temperature: 40 degrees F minimum for adhesion. Store rolls in a warm area if applying in cold weather.

Flashing

• Drip edge - Galvanized steel or aluminum, formed in an L-shape. Install at eaves UNDER the underlayment; at rakes OVER the underlayment.
• Step flashing - 4x4-inch or 5x7-inch L-shaped pieces (aluminum or galvanized steel) woven into each shingle course where the roof meets a sidewall
• Valley flashing - 24-inch wide aluminum or galvanized steel for open valleys. Valleys can also be done as closed-cut or woven.
• Pipe boots (vent flashing) - Rubber or lead collars that seal around plumbing vent pipes
• Chimney flashing - Multi-piece system: base flashing (L-shaped pieces against the chimney face), step flashing up the sides, counter flashing (embedded in or sealed to the chimney masonry overlapping the base/step flashing), cricket/saddle behind wide chimneys to divert water

Nails

• Roofing nails - Galvanized steel, 11- or 12-gauge, 3/8-inch head diameter minimum, 1-1/4 inch long for new construction (must penetrate deck 3/4 inch minimum or through deck if less than 3/4 inch)
• Coil nailers - Pneumatic nail guns loaded with coils of roofing nails. Standard on professional roofing crews.
• Hand nailing - Required by some manufacturers for certain shingle types and warranty compliance. Check the installation instructions.

Installation Procedures

Deck Inspection and Preparation

Before any roofing material goes down:

1. Walk the deck and check for soft spots, delaminated panels, rot, and protruding nails
2. Replace any damaged sheathing. Use minimum 7/16-inch OSB or 15/32-inch plywood.
3. Ensure panel edges are supported (H-clips between rafters if required)
4. Sweep the deck clean of debris and protruding fasteners
5. Verify that the deck is nailed to the framing at code-required spacing (typically 6 inches on edges, 12 inches in the field for wind zones)

Step 1 - Drip Edge at the Eaves

Install drip edge along the eaves first, before any underlayment:

• Nail every 12 inches along the top edge with roofing nails
• Overlap end joints 2 inches
• Extend the drip edge 1/4 inch past the fascia edge into the gutter

Step 2 - Ice and Water Shield (Where Required)

Apply ice and water shield along the eaves directly over the drip edge:

• Peel the release backing and press the membrane firmly onto the deck
• Overlap horizontal seams 3 inches minimum, end seams 6 inches
• Extend up the roof at least 24 inches past the interior wall line
• Apply in all valleys (full length) and around penetrations

Step 3 - Underlayment

Roll out underlayment from the eave to the ridge:

• Start at the eave, overlapping the ice and water shield by 4 inches
• Overlap horizontal courses by 2 inches (4 inches for felt)
• Overlap end joints by 4 inches (6 inches for felt)
• Fasten with plastic cap nails or staples per manufacturer's instructions
• At the ridge, overlap the underlayment from both slopes by 6 inches minimum

Step 4 - Drip Edge at the Rakes

Install drip edge along the rakes OVER the underlayment:

• This layering ensures water runs from the underlayment onto the drip edge at the rakes, and from the drip edge under the underlayment at the eaves
• Nail every 12 inches

Step 5 - Starter Strip

The starter strip provides the adhesive seal line for the first course of shingles:

• Use manufactured starter strip shingles or cut the tabs off standard shingles
• Install with the adhesive strip facing UP (toward the ridge), tight along the eave
• Overhang the drip edge by 1/4 to 3/4 inch
• Offset the end joints from the first full course of shingles

Step 6 - Field Shingles

Install shingles from the eave to the ridge:

1. Start the first course at one end of the roof, overhanging the drip edge at the eave and rake by 1/4 to 3/4 inch
2. Nail each shingle per the manufacturer's pattern. For architectural shingles: 4 nails per shingle (6 in high-wind areas), placed in the nailing zone (the thick area above the exposure line, typically 5-5/8 inches up from the bottom edge)
3. Nail placement is critical. Nails too high miss the lower layer and have no holding power. Nails too low are visible and can cause leaks. Nails must be driven flush - not over-driven (breaks the shingle) and not under-driven (sits proud and can work out).
4. Offset each course per the manufacturer's instructions. Most architectural shingles use a 6-inch offset. Some use a random offset pattern. Follow the specific instructions for your shingle.
5. Align courses using a chalk line snapped every few courses to prevent the shingles from drifting out of alignment.
6. At the ridge, trim the last course to within 2-3 inches of the ridge line.

Step 7 - Valley Installation

Valleys are the most leak-prone areas on a roof. Three methods:

• Open valley - Install ice and water shield the full length of the valley. Install 24-inch metal valley flashing over it, centered. Shingles are trimmed 3 inches from the valley center line on each side. Snap a chalk line to keep the trim line straight. Clip the upper corner of each trimmed shingle at a 45-degree angle to direct water into the valley rather than behind the shingle above.
• Closed-cut valley - Shingles from one slope extend across the valley. Shingles from the adjacent slope are trimmed 2 inches from the center line. No exposed metal. Ice and water shield required underneath.
• Woven valley - Shingles from alternating slopes are woven across the valley. Creates a smooth appearance but difficult to do well. Not recommended by many manufacturers for architectural shingles.

Step 8 - Flashing Details

Sidewall flashing (step flashing):

1. Install a piece of step flashing with each course of shingles
2. Each piece overlaps the one below by at least 2 inches
3. The bottom of each piece sits on top of the shingle course, the vertical leg goes up the wall
4. Counter flashing (siding, stucco, or metal) covers the vertical leg

Pipe penetrations:

1. Install shingles up to the bottom of the pipe
2. Slide the pipe boot over the pipe, with the flange sitting on the shingles below
3. Nail the top and sides of the flange (never the bottom - water must flow over the bottom edge)
4. Continue shingling over the top of the flange

Chimney flashing:

1. Install a continuous base flashing piece across the front face
2. Step flash up each side, weaving with shingle courses
3. Install a cricket (saddle) behind wide chimneys to prevent water pooling
4. Counter flash into the mortar joints with reglets or surface-mounted counter flashing sealed with polyurethane caulk

Step 9 - Ridge and Hip Cap

Install ridge and hip cap shingles last:

• Use manufacturer's pre-cut hip and ridge shingles, or cut architectural shingles into individual pieces
• Start at the bottom of each hip, working toward the ridge
• Start at the end of the ridge opposite the prevailing wind, working toward it
• Overlap each piece by the recommended exposure (typically 5-5/8 inches)
• Nail each piece with two nails, one on each side, 1 inch from the edge and 5-5/8 inches from the exposed butt end
• The last piece at the ridge gets a dab of roofing cement on the nail heads

Roof Ventilation

Proper ventilation extends shingle life and prevents ice dams and moisture damage in the attic:

• Balanced ventilation - Equal intake (at the soffits/eaves) and exhaust (at the ridge or near the ridge)
• Net Free Area (NFA) - Code requires 1 square foot of NFA per 150 square feet of attic floor area (or 1:300 with a vapor barrier and balanced ventilation)
• Ridge vent - A continuous vent along the ridge that allows warm air to exhaust. External baffle ridge vents are the most effective.
• Soffit vents - Perforated panels or individual vents installed in the soffit that allow cool air to enter the attic
• Do not mix vent types - Do not install ridge vents with gable vents or power vents on the same attic. Gable vents short-circuit the airflow from soffit to ridge.
• Insulation baffles - Install foam or cardboard baffles in each rafter bay at the soffit to prevent insulation from blocking the soffit vents

Other Roofing Systems (Overview)

Metal Roofing

• Standing seam and exposed-fastener panels
• Lifespan: 40-70 years. Highly wind-resistant.
• Requires specialized training for installation: panel cutting, seaming, trim details
• Expansion and contraction must be accommodated with clips and elongated holes

Flat/Low-Slope Roofing

• TPO, EPDM, and modified bitumen membranes
• Minimum slope: 1/4 inch per foot for positive drainage
• Requires specific training for membrane welding, adhesion, and flashing details

Tile and Slate

• Clay tile, concrete tile, and natural slate
• Extremely heavy (900-3,000 lbs per square). Structure must be designed for the load.
• Lifespan: 50-100+ years
• Requires specialized installation training and underlayment systems

Safety on the Roof

Roofing is among the deadliest construction occupations. Falls from roofs are the leading cause of death in residential construction.

Fall Protection Requirements

• OSHA requires fall protection for any work at heights of 6 feet or more in construction
• Personal Fall Arrest System (PFAS) - Full-body harness, shock-absorbing lanyard, and an anchor point rated for 5,000 lbs per worker. The anchor must be at or above the D-ring on your back.
• Roof brackets - Metal brackets nailed through the sheathing into the rafters, supporting a plank that provides a stable work platform on steep slopes. Used in combination with PFAS.
• Warning line systems - Allowed on low-slope roofs (4:12 or less) as an alternative to PFAS. A line set 6 feet from the edge, with flags every 6 feet.

Ladder Safety

• Extend the ladder at least 3 feet above the roof edge
• Set the base 1 foot out for every 4 feet of height (4:1 ratio)
• Secure the top of the ladder to the structure to prevent sliding
• Face the ladder when climbing. Maintain three points of contact at all times.
• Never carry materials up a ladder. Use a hoist or have someone hand materials up.

Heat and Weather Hazards

• Roof surfaces can exceed 150 degrees F in summer. Drink water constantly and take shade breaks.
• Shingles become slippery when wet. Never work on a wet, frosty, or icy roof.
• Lightning kills. Get off the roof immediately when thunderstorms approach.
• High winds increase fall risk and make material handling difficult. Most manufacturers void warranties for shingles installed below 40 degrees F (adhesive strips do not seal).

Material Handling

• A bundle of shingles weighs 60-80 lbs. Proper lifting technique is essential.
• Load materials onto the roof evenly. Do not overload one area, which can stress the structure.
• Keep the roof clean. Loose shingle wrappers, cutoffs, and nails are trip and slip hazards.
• Magnetic nail sweepers should be run at the end of every work day to pick up loose nails from the ground around the building.

Troubleshooting Common Roof Problems

Leaks

• Flashing failures - The number one cause of roof leaks. Check all flashing details: step flashing, pipe boots, valleys, chimney flashing.
• Nail pops - Nails that work up and push through the shingle above. Caused by improper nailing, wood shrinkage, or wind uplift.
• Wind damage - Lifted or missing shingles. Shingles with failed adhesive strip seals are vulnerable.
• Valley leaks - Improperly installed valley flashing or shingles cut too close to the center line.

Ice Dams

• Caused by heat escaping into the attic, melting snow on the upper roof, which refreezes at the colder eaves
• Prevention: Adequate attic insulation (R-38 to R-60), balanced ventilation, and ice and water shield at the eaves
• Ice dams cause water to back up under shingles and leak into the building

Tips from Experienced Roofers

• "Nail placement makes or breaks a roof. I've seen roofs blow off in a storm because every nail was an inch too high. Hit the nailing zone every time."
• "Don't be cheap on ice and water shield. Run it 6 feet up from the eave in cold climates, full valley length, and around every penetration. It's the cheapest insurance on the job."
• "Check the weather forecast before you tear off. Nothing worse than a stripped deck and rain rolling in. Have tarps and a plan."
• "Chalk lines keep you honest. Snap a line every 5 courses or so to check your alignment. It takes 30 seconds and saves you from laying a crooked roof."
• "Clean up every night. Roofing nails in the lawn, the driveway, or a client's tire will cost you more than you made that day."
• "On a reroof, look at the deck when you strip the old shingles. Soft spots, rot, and delaminated OSB need to be replaced before anything new goes on. Don't bury a problem."