SC Wind Zone III Roofing Requirements Explained

If you live in Myrtle Beach, North Myrtle Beach, Surfside Beach, Pawleys Island, or anywhere along the South Carolina coast, your roof must meet Wind Zone III requirements — the most demanding residential roofing standards in the eastern United States. This means your roofing system must be designed and installed for wind speeds of 130 to 150 miles per hour. Every nail, every layer of underlayment, and every fastener must meet specific standards that go well beyond what is required in Columbia, Greenville, or anywhere inland.

Understanding these requirements matters for three reasons. First, a roof that does not meet Wind Zone III standards is more likely to fail during a hurricane. Second, insurance companies can deny claims if your roof was not installed to code. Third, unpermitted or non-compliant installations create legal liability when you sell your home.

This guide breaks down every Wind Zone III requirement in plain language so you know exactly what your contractor should be doing — and what the building inspector will check.

What Is Wind Zone III?

The International Residential Code (IRC) divides the United States into wind zones based on the maximum expected wind speeds during a severe weather event. Wind Zone III is the highest category, covering areas where the basic design wind speed is 130 to 150 mph.

In South Carolina, Wind Zone III covers the coastal counties that face direct hurricane exposure:

• Horry County (Myrtle Beach, North Myrtle Beach, Conway)
• Georgetown County (Pawleys Island, Georgetown, Litchfield Beach)
• Charleston County (Charleston, Mount Pleasant, Sullivan’s Island)
• Beaufort County (Beaufort, Hilton Head Island)
• Colleton County (coastal portions)
• Jasper County (coastal portions)

Inland counties like Richland (Columbia), Greenville, and Spartanburg fall in Wind Zone I or II, with design wind speeds of 85 to 110 mph. The difference between a 110 mph and a 150 mph wind load is not proportional — wind force increases with the square of velocity, so 150 mph winds exert roughly twice the force of 110 mph winds. This is why coastal roofing requirements are so much more demanding.

The 6-Nail Fastening Pattern

The most visible difference between a Wind Zone III installation and a standard installation is the nail count. Standard installations use 4 nails per shingle. Wind Zone III requires a minimum of 6 nails per standard 3-foot shingle strip.

Why 6 Nails Instead of 4

Each nail provides a point of attachment between the shingle and the roof deck. More nails mean more attachment points, which distributes the uplift force across more fasteners. In a 130+ mph wind event, the uplift force on a single shingle can exceed 60 pounds per square foot. Six nails provide 50% more holding power than four nails, significantly reducing the chance that any single fastener failure leads to shingle loss.

Nail Placement Requirements

The 6 nails must be placed in specific locations defined by the shingle manufacturer’s high-wind installation instructions:

• One nail 1 inch from each end of the shingle
• One nail on each side of every tab slot or cutout
• All nails placed on or just below the manufacturer’s nailing line (adhesive strip area)
• Nails must be driven flush — not overdriven (breaks the mat) or underdriven (does not seat the shingle)

Nail Specifications

• Minimum length: 1-1/4 inches for new decking, 1-3/4 inches for re-roofing over existing shingles
• Head diameter: 3/8 inch minimum
• Shank type: Smooth, ring-shank, or screw-shank — ring-shank provides the best pullout resistance
• Material: Hot-dipped galvanized steel or stainless steel. Standard electro-galvanized nails corrode in salt air. Stainless steel Type 304 or 316 is recommended within 3 miles of the ocean.
• Deck penetration: 3/4 inch minimum through the decking, or the nail must pass completely through if decking is thinner than 3/4 inch

Enhanced Underlayment Requirements

Wind Zone III requires more robust underlayment than inland areas. The underlayment is your second line of defense if the primary roofing material is compromised during a storm. In coastal SC, the underlayment system must be capable of protecting the roof deck from wind-driven rain even if shingles are missing.

Self-Adhering Ice and Water Shield

Self-adhering membrane (commonly called ice and water shield) must be installed in the following locations:

• All eaves — Extending at least 24 inches past the interior wall line (this typically means 3 to 4 feet up from the eave edge)
• All valleys — A minimum of 36 inches wide centered on the valley line
• Around all penetrations — Pipes, vents, chimneys, skylights, and any other openings through the roof deck
• At ridges and hips — Where ridge vent or hip cap will be installed
• At rake edges — Along the gable ends where wind-driven rain exposure is highest

Synthetic Underlayment on the Field

The remaining roof deck area (the “field”) must be covered with at least one layer of approved synthetic underlayment or two layers of 15-pound asphalt-saturated felt with staggered joints. Synthetic underlayment is the modern standard because it is tear-resistant, does not absorb water, and lies flat during installation.

Synthetic underlayment must be fastened with capped nails or staples per the underlayment manufacturer’s specifications. In high-wind areas, cap staples or cap nails are required — standard staples alone do not provide enough holding power.

Full Sealed Roof Deck Option (FORTIFIED Standard)

While not required by code, the IBHS FORTIFIED Roof standard requires self-adhering membrane or sealed underlayment across the entire roof deck, not just at eaves and valleys. This creates a fully waterproof secondary barrier that protects the structure even if the primary roofing material is completely stripped during a Category 3+ hurricane. This upgrade adds $1,000 to $3,000 to a standard installation but qualifies for 15 to 30% insurance premium reductions in South Carolina.

Roof Deck Fastening Requirements

The connection between the roof deck (plywood or OSB sheathing) and the roof framing is a critical load path for wind resistance. Wind Zone III requires enhanced deck fastening schedules:

• Minimum deck thickness: 7/16-inch OSB or 15/32-inch plywood (CDX grade minimum)
• Fastener type: 8d ring-shank nails (2-3/8 inches) or approved deck screws
• Edge spacing: 6 inches on center along all panel edges
• Field spacing: 6 inches on center at all intermediate supports (rafters or trusses)
• Panel gap: 1/8-inch expansion gap between panels to prevent buckling

Note that the standard fastening schedule for lower wind zones is 6 inches at edges and 12 inches in the field. Wind Zone III cuts the field spacing in half, requiring twice as many fasteners through the body of each panel. During a re-roof, the inspector will check that existing deck fastening meets current standards or has been upgraded.

Ridge Cap and Hip Requirements

Ridge caps (the shingles along the peak) and hip caps are among the most vulnerable points on any roof during high winds. Wind accelerates as it crosses the ridge, creating intense uplift pressure. Wind Zone III has specific requirements:

• Ridge shingles must be rated for the design wind speed — Not all ridge cap products are rated for 130+ mph. GAF TimberCrest, Owens Corning DecoRidge, and similar high-profile ridge products are designed for high-wind applications.
• Fastener pattern for ridge caps: Two nails per ridge shingle minimum, with nails placed in the manufacturer’s specified high-wind location
• Sealant: Asphalt roofing cement at the bond line of each ridge shingle in addition to mechanical fastening
• Ridge vent compatibility: If a ridge vent is installed, it must be rated for the design wind speed and installed per the manufacturer’s high-wind instructions. Improperly installed ridge vents are a common point of failure.

Flashing and Drip Edge Requirements

Flashing requirements in Wind Zone III go beyond the basic IRC specifications:

• Drip edge on all edges — Metal drip edge is required along all eaves and rakes. Minimum 26-gauge galvanized steel or equivalent. In the coastal salt zone, painted aluminum or stainless steel is recommended to prevent corrosion.
• Step flashing at wall intersections — Individual step flashing pieces must be a minimum of 4 inches wide on each leg. Counter-flashing is required over step flashing at all masonry walls.
• Valley flashing — Open metal valleys require a minimum 24-inch wide metal valley liner over ice and water shield. Closed-cut valleys are permitted but must follow the manufacturer’s high-wind installation method.
• Pipe boot and penetration flashing — All pipe boots must be secured with screws (not nails) and sealed with polyurethane caulk rated for roofing applications. Standard rubber boots degrade faster in coastal UV exposure — EPDM or silicone pipe boots are recommended.

Metal Roofing Requirements in Wind Zone III

Metal roofing has different code requirements than asphalt shingles in Wind Zone III:

Standing Seam Metal

• Panels must be tested and rated for the site-specific design wind speed per ASTM E1592 or UL 580
• Concealed clips must be spaced per the manufacturer’s high-wind installation guide (typically 12 to 24 inches on center)
• Clip material must be compatible with the panel material to prevent galvanic corrosion
• Seam type (mechanical lock vs snap-lock) must be rated for the design wind speed
• Panel gauge must be appropriate for the span between clips at the required wind rating

Exposed-Fastener Metal

• Screws must have bonded EPDM washers (neoprene degrades in coastal UV)
• Screw spacing per manufacturer’s high-wind schedule (typically every rib in the flat of the panel)
• Panel overlap must follow the manufacturer’s high-wind requirement (typically 2 ribs minimum on end laps)
• Sealant tape at all panel overlaps

For complete details on coastal metal roofing, see our coastal metal roofing guide.

Permits and Inspections in Horry County

All roof replacements in Horry County and the City of Myrtle Beach require a building permit. Here is what the process involves:

Permit Application

• Application submitted by the licensed contractor (not the homeowner)
• Must include scope of work, material specifications, and wind rating documentation
• Permit fee typically $100 to $300 depending on project value
• Processing time: 1 to 5 business days for standard re-roofing

Required Inspections

Horry County typically requires the following inspection stages for a re-roof:

• Deck inspection — After old roofing is removed and before new underlayment is installed. Inspector verifies deck condition, fastening, and any necessary repairs.
• Underlayment/dry-in inspection — After underlayment is installed but before the primary roofing material. Inspector verifies ice and water shield placement, underlayment type and fastening, and drip edge installation.
• Final inspection — After all roofing is complete. Inspector checks material installation, fastener pattern, ridge caps, flashing, and overall workmanship.

Failing an inspection means the contractor must correct the deficiency and call for re-inspection. A competent contractor who installs to Wind Zone III standards consistently passes all inspections on the first try.

Most Common Wind Zone III Violations

Based on inspection reports and our experience repairing improperly installed roofs in the Myrtle Beach area, these are the most common code violations:

• 4-nail pattern instead of 6 — The most frequent violation. Often caused by crews trained in inland markets who default to standard patterns.
• Overdriven nails — Pneumatic guns set too high, driving nails through the shingle mat and reducing holding power to near zero.
• Missing or insufficient ice and water shield — Skipping the ice and water shield at eaves or valleys to save material cost.
• Standard felt instead of synthetic underlayment — Using a single layer of 15-pound felt where code requires either synthetic or double-layered felt.
• Non-rated ridge caps — Using cut 3-tab shingles as ridge caps instead of manufactured high-wind ridge products.
• Missing drip edge — Omitting drip edge at rake edges (gable ends), especially on re-roofs where the original roof may not have had drip edge.
• Electro-galvanized nails — Using standard electro-galvanized nails instead of hot-dipped galvanized or stainless steel. The thinner zinc coating on electro-galvanized nails corrodes within a few years in salt air.

Frequently Asked Questions

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