How to Seal Metal Roof Seams (Corrugated & Standing Seam)

Metal roof seams are the most common source of leaks on metal roofing systems. Every lap joint, ridge cap connection, and penetration flashing relies on sealant to keep water out, and that sealant does not last forever. In Myrtle Beach, where temperatures swing from 95 degrees in summer to 30 degrees on winter nights, the constant thermal expansion and contraction of metal panels stresses every seam on the roof — and eventually, something gives.

Whether you are dealing with a corrugated metal roof on a commercial building or a standing seam system on a residence, the principles of proper seam sealing are the same: choose the right sealant, prepare the surface correctly, and apply it with the right technique. This guide walks through the complete process for both corrugated and standing seam metal roofs, with specific attention to the coastal conditions that affect metal roofs in our area.

For extensive seam work or standing seam systems, we always recommend hiring an experienced metal roofing contractor in Myrtle Beach. But for minor repairs on accessible corrugated roofs, this guide gives you everything you need.

Why Metal Roof Seams Fail

Understanding why seams fail helps you choose the right fix and prevent future problems.

• Thermal movement: Metal expands when heated and contracts when cooled. A 20-foot steel panel can move nearly 1/4 inch between a hot summer day and a cold winter night. This constant movement works sealant back and forth, eventually breaking the bond
• UV degradation: Sealants exposed to direct sunlight break down over time. UV radiation causes most sealants to harden, crack, and lose adhesion within 5 to 15 years
• Improper sealant choice: Using the wrong sealant is the number one cause of premature seam failure. Standard silicone caulk, latex caulk, and general-purpose sealants are not designed for metal roofing and will fail within 1 to 3 years
• Poor surface prep: Sealant applied to dirty, oily, or oxidized metal will not bond properly regardless of the product quality
• Fastener back-out: Screws that loosen from thermal cycling create gaps around the fastener hole, allowing water to bypass the sealant entirely
• Salt air corrosion: In coastal South Carolina, salt deposits on metal surfaces can interfere with sealant adhesion and accelerate corrosion around fastener points

Metal Roof Sealant Types: Which to Use

Butyl Tape Sealant (Best for Concealed Seams)

Butyl tape is a pressure-sensitive adhesive tape that comes in rolls, typically 1/2 inch to 1 inch wide. It is the standard sealant used between overlapping metal panels during initial installation. Butyl tape remains permanently flexible, does not harden or crack, and maintains its seal through the full range of thermal movement that metal roofs experience. Lifespan: 20 to 30 years. Cost: $15 to $30 per roll (enough for 30 to 50 linear feet).

Polyurethane Sealant (Best for Exposed Repairs)

Polyurethane sealant (such as Sika 1a, Titebond Metal Roof Sealant, or Geocel 2300) is the best caulk-tube sealant for metal roof repairs. It bonds strongly to painted and bare metal, remains flexible after curing, and has good UV resistance. Polyurethane can be tooled for a clean finish and painted if needed. Lifespan: 15 to 20 years. Cost: $8 to $15 per 10 oz tube.

Silicone Sealant (Good for UV-Exposed Areas)

100 percent silicone sealant offers the best UV resistance of any sealant type. It does not yellow, harden, or crack from sun exposure. However, silicone does not adhere as strongly to painted metal surfaces as polyurethane and cannot be painted over. Use silicone when the seam will be permanently exposed to direct sunlight and where adhesion is not the primary concern (e.g., over butyl tape as a secondary weather barrier). Lifespan: 20 to 25 years for UV resistance. Cost: $6 to $12 per tube.

What NOT to Use

• Latex caulk: Becomes brittle and cracks within 1 to 2 years on metal. Has zero flexibility for thermal movement
• Acrylic caulk: Slightly better than latex but still fails within 2 to 3 years on metal roofs
• Roofing tar or asphalt cement: Becomes brittle, does not bond well to metal, and creates a mess that makes future repairs difficult
• General-purpose "all surface" sealants: These are designed for light-duty indoor applications and fail quickly in the outdoor thermal and UV environment

Surface Preparation: The Step Most People Skip

Surface prep determines whether your sealant lasts 15 years or 15 months. Even the best sealant will fail if applied to a dirty or contaminated surface. Here is the proper prep sequence:

1. Remove old sealant: Scrape off any existing sealant with a plastic scraper or putty knife. Do not leave old sealant under the new application — it will not bond properly
2. Wire brush the seam: Use a stiff wire brush to remove rust, oxidation, loose paint, and debris from both sides of the seam. For heavy corrosion, use a 80-grit sandpaper or abrasive pad
3. Clean with denatured alcohol or acetone: Wipe the entire seam area with a solvent-dampened cloth to remove oil, dust, salt deposits, and any remaining contaminants. Let the solvent evaporate completely (2 to 3 minutes) before applying sealant
4. Verify the surface is dry: Do not apply sealant to damp or wet surfaces. In Myrtle Beach, morning dew can linger on metal surfaces until mid-morning. Wait for the surface to be completely dry
5. Apply primer if recommended: Some polyurethane sealants recommend a metal primer for maximum adhesion. Check the product data sheet and follow the manufacturer's instructions

How to Seal Corrugated Metal Roof Seams

Corrugated metal roofs have two main types of seams: horizontal lap seams (where one panel overlaps the end of the panel below) and side lap seams (where the edge of one panel overlaps the adjacent panel). Both require proper sealing.

Horizontal Lap Seams (End Laps)

1. Clean and prep the overlap area following the steps above
2. Apply a continuous bead of butyl tape sealant along the top edge of the lower panel, approximately 1 inch from the edge
3. Set the upper panel into position, overlapping by a minimum of 6 inches (8 to 12 inches is better for low-slope roofs)
4. Fasten through both panels using screws with neoprene washers, driving through the high ribs (not the valleys)
5. Check that the butyl tape is compressed evenly by looking for a slight squeeze-out along the seam edge. Trim any visible excess
6. For additional protection in high-rain areas like Myrtle Beach, apply a bead of polyurethane sealant along the exposed edge of the upper panel

Side Lap Seams

1. Clean the overlapping edge of both panels
2. Apply butyl tape sealant along the underlapping panel's raised rib, where the overlapping panel will sit
3. Press the overlapping panel into position over the sealant
4. Fasten through both panels at the overlapping rib with neoprene-washer screws every 12 to 18 inches
5. Ensure the overlap runs in the direction away from prevailing wind. In Myrtle Beach, panels should lap so that wind blows over the seam, not into it

How to Seal Standing Seam Metal Roof Seams

Standing seam metal roofs are fundamentally different from corrugated because their seams are mechanically folded rather than overlapped and fastened. This makes them inherently more water-resistant but also more complex to repair.

Common Standing Seam Leak Points

• Seam tops at ridge: Where the vertical seams meet the ridge cap is the most common leak point. Thermal movement can open small gaps at this junction
• Panel end laps: On longer roofs where panels must be joined end-to-end, the horizontal junction is a potential leak source
• Penetration flashings: Around pipes, vents, and equipment curbs where the standing seam panels are cut and terminated
• Eave and gable transitions: Where the panels meet the edge flashings at the perimeter of the roof

Repair Technique for Standing Seam Leaks

1. Identify the exact leak location by inspecting from inside during rain or using a hose test
2. Clean the seam area thoroughly with wire brush and solvent
3. For minor gaps at seam tops or caps, apply a thick bead of polyurethane sealant along the seam, tooling it into the gap and feathering the edges
4. For seams that have opened slightly, a seam repair tape (butyl or modified bitumen tape, 4 to 6 inches wide) can be applied over the seam after cleaning and priming
5. For significant seam failures, the seam may need to be mechanically re-closed using a hand seamer tool, then sealed with butyl tape inside the fold

Coastal South Carolina Considerations for Metal Roof Seams

Metal roofs in Myrtle Beach face unique challenges that affect seam integrity and sealant longevity.

• Salt air corrosion: Salt deposits on metal surfaces create a barrier that prevents sealant adhesion. Always wash the seam area with fresh water and solvent before applying sealant. Homes within 1 mile of the ocean should have seams inspected annually
• Galvanic corrosion: When dissimilar metals contact each other in the presence of salt moisture, galvanic corrosion accelerates. Use sealants as an insulating barrier between dissimilar metals (e.g., aluminum flashing on steel panels)
• Wind-driven rain: Myrtle Beach experiences tropical storms with horizontal rain. Seams must be sealed on the weather-facing side and overlaps must be oriented to shed wind-driven rain rather than trap it
• Extreme thermal cycling: Metal roof surface temperatures can reach 160 degrees in summer and drop to 25 degrees in winter. Choose sealants rated for at least -20F to 250F temperature range

When to Call a Professional

While minor seam repairs can be a DIY project, certain situations require a professional metal roofing contractor:

• Standing seam roofs that require mechanical re-seaming
• More than 3 to 4 seams needing repair (indicates a systemic problem, not isolated failure)
• Ridge cap or hip cap leaks where multiple panels converge
• Leaks around penetrations (pipes, vents, skylights) that require custom flashing work
• Steep-slope roofs where fall protection is required
• Active rust or corrosion around seam areas that needs treatment before sealing
• Any seam work that could affect the manufacturer's warranty
• Commercial roofs where building code requires licensed contractor work

A professional metal roof seam repair in Myrtle Beach typically costs $300 to $800 for a few isolated seams, or $1,500 to $4,000 for comprehensive re-sealing of an entire roof. The cost depends on the number of seams, roof accessibility, and the type of metal roofing system.

Frequently Asked Questions

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