Building in coastal regions presents a different set of challenges than some other areas of the country. Having to deal with salt spray and hurricane-force winds and rain makes metal roofing a good option for homeowners. Its strength, longevity and low maintenance are all reasons why metal is able to take on the weather in coastal regions while maintaining its style and design.
Choosing the right type of metal roofing can offer durability and longevity in a notoriously tough environment
Photo courtesy of NS Bluescope Coated Products-North America.
Coastal Design Factors
According to Charles “Chip” McGowan, president of RHEINZINK America Inc., Woburn, Mass., there are several key factors to consider when choosing the right metal roofing for coastal regions and marine environments. These include resistance to chlorine (salt); dynamic appearance; climate zone, associated rainfall and maintenance requirements; performance requirements; and warranty.
While the actual distance a building is from salt water is important, so is the average rainfall, amount of fog, breaking surf or calm waters, and prevailing winds. Michelle Vondran, technical manager at NS BlueScope Coated Products–North America, Kalama, Wash., says, “An area with high rainfall will get lots of natural rinsing and is a better scenario than low rainfall, likewise, areas such as the Puget Sound with no breaking surf (low salt spray) and high rainfall is considering a milder marine environment than say the southern coast of California with strong surf (high salt spray) and low rainfall. All of these factors influence the frequency and type of cleaning and maintenance that may be required to ensure good long-term performance.”
If not properly protected, some metals will corrode from the salt in the atmosphere. “White deposits from salt in the atmosphere can develop on all metal roofing materials,” McGowan says. “Lighter-colored coatings and substrates, including natural metals such as zinc, show salt less. Natural metals will form a protective patina. The patina in marine environments is usually lighter in color because of chlorides found in the atmosphere.”
Materials such as zinc complement both contemporary and traditional architectural styles while fostering a connection to their surrounding natural environment. “Untreated, architectural-grade zinc is bright, shiny and light reflective,” McGowan explains. “Over time, a natural matte patina develops, creating a dynamic appearance as the material ages. A patina’s formation is a process of the gradual growing together of zinc carbonate ‘freckles.’ The rate of its formation is related to the slope of the surface. The patina will form slower on a vertical wall surface than on a slightly pitched roof. The patination speed varies between six months and five years or more, depending on climatic conditions. The more exposure to wetting and drying cycles, the quicker the patina will develop.”
Randy Tweedt, field service tech coordinator–East at Houston-based Cornerstone Building Brands, adds that it is important for the panel type to be able to handle the required wind loads based on the building’s proximity to the body of saltwater. The roofing system should be tested to withstand the required building codes. Adds McGowan, “For many coastal regions, this means this means having a system tested to meet high winds and hurricane conditions.”
A private residence in Fredericia, Denmark. (Photo courtesy of RHEINZINK)
Materials and Profiles
When it comes to choosing a metal roof panel for a project in a coastal environment, decisions need to be made on the type of substrate, paint system and more. “The substrate type, paint system, accessories and design are all very important when building in a coastal area,” says Vondran. “These items need to be discussed early to ensure that the appropriate materials are specified and are available, as extra lead time may be needed. Reputable panel suppliers should have coastal or marine options available and be able to determine if the specific building site qualifies as a coastal environment.”
McGowan says the decision should be based on a specific metal’s proven performance in that climate. “Natural metals and certain specialty stainless steel alloys will perform better than coated materials because they do not rely on an additional coating to protect their substrates,” he adds.
While Tweedt notes that steel is fine with the proper substrate finish and top coat based on a building’s proximity to salt water, Vondran adds that painted aluminum is probably the best choice due to the corrosion resistance of the aluminum. “Next best would be painted Galvalume utilizing a coastal paint system, which usually consists of a high build primer and/or clear coat, followed by painted galvanized,” she says.
Additionally, galvanic corrosion between dissimilar metals is a major concern and can impact the performance of a metal roof in coastal regions, making accessory and fastener choices crucial. “Stainless components should not be in direct contact with aluminum, Galvalume or galvanized metal panels; it will cause early corrosion failure,” explains Vondran. “Panel manufacturers can provide guidance on the best choices for accessory materials.”
Once a substrate material is decided upon, it’s important to ensure that the panel profile allows for good water drainage, as standing water can be detrimental and standing salt water can cause panel failure. “Concealed fastener profiles are strongly encouraged as they minimize exposed penetrations, edges and fasteners to the corrosive environment,” Vondran explains. “Field-cut edges should be avoided if possible and if they do occur, they should be covered with trim or an edge clear coat seal to help minimize corrosion. The fewer discontinuities, cuts and penetrations, the better.”
The Forrestal residence in Cape Coral, Fla., features MBCI’s 5V Crimp metal roofing in Galvalume. (Photo courtesy of Cornerstone Building Brands)
Roof Slopes
While all roof slopes and shapes can be suitable in coastal regions, Jason T. Allen, research and development manager at Houston-based MBCI, recommends having the roof system designed by a professional engineer to determine which panel profile would work best based on roof slope, roof type, wind speed, eave height and substrate. A professional engineer can also help determine the proper spacing and material thickness needed for a metal roof’s framing and substructure. Additionally, McGowan says the substructure may require enhancements to meet corrosion-resistant framing or special fire code requirements in certain coastal regions.
However, Vondran recommends a slope of at least 1/4:12 to allow for good drainage. “If the specific region is low in rainfall a higher slope is better,” she says. “The overall design should allow for good water shedding as well as ease of required maintenance. Sheltered areas, such as under eaves, will need to be accessible for freshwater cleaning.” For zinc roofs, McGowan recommends having a structured underlay. “This creates an air space that facilitates the movement of moisture to flow away or evaporate.”
A private residence in Hingham, Mass. (Photo courtesy of RHEINZINK)
Coatings and Warranties
Different paint systems can vary widely in their performance in coastal environments. It’s important to consult with manufacturers for performance and warranties when deciding on metal panel coatings. And, as Tweedt notes, if a building is within 1,500 feet of a body of salt water, then a special coastal finish should be specified.
Vondran notes that most paint suppliers offer a marine or coastal paint system, which are typically PVDF systems that usually consists of a high build primer and maybe a clear coat. “The definition of coastal does vary by supplier as does warranty duration, so read the fine print carefully,” she says. “The specific substrate may also impact the paint requirements and warranty duration. If the site is within one mile of salt water, it’s probably best to have it reviewed by the panel manufacture to verify if it qualifies as coastal/marine and confirm warranty coverage.”
If a coating is scratched, McGowan notes that integrity of the metal can be affected, and the warranty can be voided. And regardless of the coating, metal roofs in coastal areas still need to be cleaned regularly. As always, it is recommended to follow the manufacturer’s cleaning instructions. While some regions receive enough rainfall to sufficiently and naturally rinse salt and particulates off of a metal roof, McGowan says for aesthetic reasons it’s recommended to clean the surface of zinc materials with clean water—not seawater—at least twice a year in coastal regions, depending on local conditions. “If the metal is scratched, scuffed or fingerprinted, zinc will heal itself by re-patinating. With time and exposure to wetting and drying cycles, the former blemish will patinate and blend to match.”
“Collaboration between architects, specifiers, contractors, manufacturers, fabricators and installers will help ensure a roof that provides long-lasting functionality and appearance, achieving the best results for the building owner,” says McGowan.