Metal roof leaks can become a significant issue if left unchecked, leading to water damage and costly repairs. Understanding the common reasons behind these leaks is essential for preventive maintenance and timely repairs. This guide details five typical reasons for metal roof leaks, from roofing fasteners to missing sealants, providing insights into each cause and how to address it effectively.

1. Roofing Fasteners Made of Metal

One of the most frequent causes of leaks in metal roofs is improperly installed or maintained roofing fasteners, particularly screws. Metal roofing screws are designed with a rubber washer at the base, which acts as a gasket to prevent water from seeping through. When the screw is fastened into the metal roofing panel, this rubber washer forms a seal, blocking moisture from reaching the vulnerable areas beneath. However, despite their simple design, screws can often be under-driven, over-driven, or driven at incorrect angles, leading to compromised seals and potential leaks.

Over-Driven Screws

Over-driving screws can happen when they are fastened too tightly into the panel. This can lead to the screw head pressing too firmly against the roofing material, causing the rubber washer to break or shift out of place. When this washer moves, it no longer provides an effective seal, allowing water to seep through the opening. Over-driven screws also risk damaging the roofing panel itself, which can further increase the chance of leaks developing.

Under-Driven Screws

If screws are under-driven, meaning they are not screwed in tightly enough, they may fail to compress the rubber washer against the metal surface properly. This lack of compression means that the washer cannot form an adequate seal, leaving gaps for water to enter. Under-driven screws are commonly a result of incorrect torque settings on the drill or a lack of attention during installation.

Screws Driven at Incorrect Angles

Achieving a proper seal also depends on the angle at which screws are driven into the roof. When screws are driven at an incorrect angle, the rubber washer cannot sit flush against the metal surface, compromising its ability to block water. This improper angle can leave small spaces open around the washer, leading to leaks over time, especially during heavy rainfall or storms.

Missing the Framing Component

Sometimes, screws might completely miss the metal strut or wood framing below, providing no solid anchor point. Without something to grip onto, the screw doesn’t form a tight seal, and leaks can become difficult to spot since the screw might appear properly in place but isn’t effectively securing the metal panel.

Wear and Tear on Screws

Over time, even well-driven screws can begin to fail. Rubber washers degrade due to exposure to the elements, losing elasticity and cracking. As the washers wear out, they can no longer form a watertight seal, making it necessary to replace or re-tighten screws periodically to prevent leaks from forming around them.

2. Stack Flashings

Another vulnerable area for metal roof leaks is stack flashings, which are rubber or synthetic boots installed around pipes, vents, and other roof protrusions. Stack flashings are essential for sealing around these points, but they tend to wear out faster than the metal roof panels due to exposure to heat and the natural movement of the roof. Metal roofs expand and contract with temperature changes, placing strain on stack flashings, which can cause them to crack or split over time.

Once stack flashings start to deteriorate, water can easily penetrate through the compromised areas around the pipes and vents, causing leaks. Replacing worn or damaged stack flashings is necessary to maintain the integrity of the roof. Regular inspections can help identify stack flashings that may be close to failing, allowing for preemptive replacements.

3. Missing Sealants

During the installation of a metal roof, contractors often use sealants to waterproof certain parts of the roof. These sealants are usually applied in areas where metal panels meet other roofing components, creating an additional layer of protection. However, sealants typically have a shorter lifespan than the metal roof itself and will require replacement over time. Regular maintenance checks can identify worn-out sealants, allowing you to address potential leak points before they lead to larger issues.

Common Areas Needing Sealants

• Metal Ridge Caps: Metal ridge caps are installed at the peak where two roof slopes meet, sealing the highest point of the roof. Over time, these caps can shift or lose their seal, making it crucial to reapply sealant as needed.
• Z-Flashings: Installed to prevent water from entering horizontal seams between metal sheets, Z-flashings are essential for waterproofing roof transitions and should be resealed periodically.
• Roof Transitions: Where two different roof pitches meet, transition flashings are used to keep water from entering. Both inner and outer closures are sealed to prevent leaks at these vulnerable points.
• Counter Flashings: Located on walls or curbs, counter flashings cover the top edge of base flashings. If the sealant around these edges fails, water can penetrate and cause internal damage.
• Reglets: Found at the point where a roof meets a wall, reglets work in conjunction with counter flashings to keep water from entering the roof’s edges. Maintaining this seal is essential for long-term waterproofing.
• Pitch Pans: Pitch pans are small, open-bottomed containers filled with mastic, used to seal around penetrations in the roof. When these fill materials degrade, leaks can quickly form, so regular inspections and refills are necessary.

4. Panel Damage or Corrosion

Metal roof panels are designed to withstand tough weather conditions, but over time, exposure to the elements can take its toll. Physical damage from falling debris, hail, or heavy winds can dent or puncture panels, creating entry points for water. Additionally, if panels aren’t adequately coated, they can start to corrode, especially in humid or salty environments. This corrosion weakens the metal and may cause holes or cracks that allow water to seep through.

When corrosion or damage to panels is detected, it’s important to replace or repair affected areas promptly to avoid further deterioration. Regular maintenance and protective coatings can also help slow down the process of corrosion, extending the life of metal roofing panels.

5. Poor Installation Practices

The effectiveness of a metal roof largely depends on the quality of its installation. Poor installation practices can introduce vulnerabilities from the start, leading to leaks much sooner than expected. Issues such as improperly aligned panels, insufficient overlaps, or incorrect fastening can all contribute to water infiltration.

Hiring a reputable contractor with experience in metal roofing installations can prevent many of these issues. Proper installation includes ensuring that panels overlap adequately, fasteners are correctly positioned, and any flashing and sealants are correctly applied. Periodic inspections can also help identify and address any areas where poor installation may be causing problems.

4. Curb Flashings

When HVAC systems are installed on a metal roof, they are typically placed on top of a roof curb. This curb is a metal frame designed to support the HVAC unit and connect ducting efficiently. However, one of the most common areas for leaks to form on metal roofs is around these roof curbs. Even if flashing is properly installed around the curb, water can eventually find its way through, especially on the curb’s upward-facing side, due to the constant exposure to water runoff.

Regular inspection and maintenance of curb flashings are necessary to prevent leaks in these areas. Ensuring the flashing is securely sealed and promptly repairing any damage can help protect the roof from water infiltration around the HVAC curb.

5. Seams & Overlaps

Seams and overlaps are natural weak points on metal roofs where panels meet. When first installed, these areas must be tightly sealed to prevent water from seeping in. Over time, however, these joints may start leaking due to a phenomenon known as capillary pull. Capillary pull, or capillary action, occurs when water travels in microscopic spaces between two surfaces, such as where metal sheets overlap. This effect can cause water to move upward against gravity, entering between the roof panels.

During installation, rubber or mastic seals are typically applied around fasteners between roof sheets to counteract capillary pull. However, these seals can degrade over time due to the roof’s natural movement from weather, temperature changes, or heavy weight from water or snow buildup. This makes routine maintenance and inspection crucial for preventing leaks at the seams and overlaps of a metal roof.

How to Repair Metal Roof Leaks

Repairing metal roof leaks effectively involves using suitable methods and materials to address the specific causes of leakage. Below are some reliable solutions for repairing metal roof leaks.

Roof Sealant

Roof sealants are a quick and temporary solution for repairing metal roof leaks. These sealants can prevent moisture from entering the structure and shield the roof from UV radiation. Roof sealants are especially helpful for patching small leaks and preventing more extensive damage, such as rot and mildew.

For example, the Terminator Roof Sealant by American WeatherStar is a moisture-cure solution specifically designed to perform well in challenging weather conditions, making it an effective choice for immediate leak repairs.

Removing and Replacing Screws

As discussed, improperly installed or old screws can lead to leaks. Over time, screws may become loose or back out due to natural wear and tear, resulting in water ingress. If screws are found to be over-driven, under-driven, or driven at incorrect angles, they will need to be removed and replaced with new fasteners. This repair method, while effective, is labour-intensive, requiring careful attention to detail to ensure each screw forms a proper seal against the metal panel.

Roof Coating (Roof Restoration)

Roof coatings provide an excellent restoration solution for metal roofs. A fluid-applied coating system, which forms a protective layer over the existing roof, can extend the roof’s lifespan by 10 to 20 years, depending on the coating’s type and thickness. This method does not require a complete tear-off and is therefore more cost-effective than a full roof replacement. Roof coatings are particularly useful for preventing leaks and providing additional protection against harsh weather conditions.

Applying a roof coating involves cleaning the roof surface, applying a waterproof mastic to seal small gaps, and then applying the coating over the entire roof. This process helps to protect the roof from water damage and UV exposure, effectively reducing the likelihood of leaks.

SPF (Spray Foam Roofing)

Spray polyurethane foam (SPF) roofing is another viable option for repairing metal roofs. SPF can be applied directly over an existing metal roof, forming a seamless and insulated barrier that prevents leaks. Unlike traditional coating systems, SPF provides additional benefits such as thermal insulation, helping to improve the building’s energy efficiency.

This spray foam roofing method creates a solid, protective layer over the metal, covering minor imperfections and preventing water infiltration. SPF is particularly useful for commercial properties seeking both waterproofing and insulation benefits.

Roof Replacement

In cases of extensive roof damage, such as widespread rust or multiple loose panels, a roof replacement may be necessary. If a metal roof is over a decade old or has significant damage, repairing individual components may not be sufficient. Here are a few signs that indicate a roof replacement is the better option:

• Extensive Rust: Rust signifies that the protective coating on the metal roof has deteriorated, allowing water and moisture to corrode the metal underneath. Once the coating is compromised, leaks will likely become more frequent, and replacing the roof becomes a more practical solution.
• Loose Panels: While a few loose panels can often be re-secured, a large number of loose or damaged panels may indicate structural issues. If neglected, these panels can lead to further deterioration, ultimately necessitating a roof replacement.
• Widespread Leaking: Persistent leaks caused by rust, loose panels, or missing fasteners may point to a fundamental issue with the roof’s installation or condition. In such cases, attempting to patch individual leaks may be a temporary fix at best, and replacing the roof will provide a more durable, long-term solution.

Installing Metal Roof Patching

For isolated areas of damage, metal roof patches can be a cost-effective and durable solution. This method involves cutting a piece of metal that matches the damaged area and securing it over the leak. The patch is sealed with a roofing adhesive or waterproof sealant, then fastened with metal screws to ensure a tight bond with the existing roof panel. Metal patches are particularly useful for covering punctures or small holes caused by falling debris or corrosion.

To install a metal roof patch:

1. Clean the Damaged Area: Remove any rust, dirt, or debris to ensure a smooth surface for patch adhesion.
2. Apply Sealant: Use a waterproof roofing adhesive or sealant around the edges of the patch to create a watertight seal.
3. Attach the Patch: Place the metal patch over the damaged area, securing it with metal screws. Ensure screws are evenly spaced and not over-driven to prevent further leaks.
4. Seal Around the Patch: Once installed, apply an additional layer of sealant around the edges of the patch to reinforce waterproofing.

This method is highly effective for smaller, localised leaks and can extend the life of the roof without the need for major repairs or replacements. Regular inspection of patched areas is recommended to ensure the seal remains intact over time.

Conclusion

Metal roof leaks can result from various factors, including improperly sealed seams, faulty fasteners, degraded curb flashings, and worn-out roof coatings. Understanding these causes and implementing appropriate repair methods, such as using roof sealants, applying coatings, or even considering full roof replacements, can help maintain the integrity of a metal roof and prevent costly water damage. Regular inspections and timely repairs are key to prolonging the lifespan of a metal roof and ensuring a leak-free, weather-resistant structure.