Factors For Specifying Metal in Coastal Regions
Marine environments are tough when trying to specify materials. The mix of moisture, sea spray, and salt can all lead to corrosion and require special considerations. Read this Q and A to get a handle on what you should be considering when specifying metal in coastal regions.
Q – What is the most important thing to plan for when specifying metal roofing in coastal regions?
A – Substrate type, paint system, accessories, and design are all very important when building in a coastal area. These items need to be discussed early to ensure that the appropriate materials are specified and are available; 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.
Q – What factors are in play when choosing metal roofing for coastal regions?
A – Actual distance from saltwater is important, but so is average rainfall, amount of fog, breaking surf or calm waters, and prevailing winds. 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 these factors influence the frequency and type of cleaning and maintenance that may be required to ensure good long-term performance.
Q – What type of metal roofing materials are better suited to coastal regions and why?
A – 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.
Dissimilar metals, or galvanic corrosion, is a huge concern and can greatly impact the performance of a metal roof in coastal settings 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. Panel manufacturers can provide guidance on the best choices for accessory materials.
Q – Are there certain metal panel profiles that are more suited to coastal regions? Why or why not?
A – Profiles that allow for good water drainage are crucial; standing water is quite detrimental and standing saltwater can cause failure quickly. Concealed fastener profiles are strongly encouraged as they minimize exposed penetrations, edges, and fasteners to the corrosive environment. 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.
Q – Are there certain roof slopes, shape, pitch, etc., that are more suited to coastal regions? Why or why not?
A – A slope of at least ¼:12 is recommended to allow for good drainage. If the specific region is low in rainfall a higher slope is better. 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.
Q – How are framing and substructure requirements for metal roofs different in coastal regions?
A – Framing and substructure requirements are the same in coastal regions and will be dictated by local building codes.
Q – What do architects and specifiers need to know about coatings and paint systems for metal roofs in coastal regions?
A– Most paint suppliers offer a marine or coastal paint system, and they usually consist of a high build primer and maybe a clear coat and are typically PVDF systems. The definition of “coastal” does vary by supplier as does warranty duration, so read the fine print carefully. The specific substrate may also impact the paint requirements and warranty duration. If the site is within one mile of saltwater, it is probably best to have it reviewed by the panel manufacturer to verify if it qualifies as coastal/marine and confirm warranty coverage.
Q – What type of environmental concerns are in play in coastal regions that architects should be aware of?
A – Environmental concerns are usually the same as non-coastal regions, but local restrictions and requirements could exist.
Q – What type of product approvals are necessary for metal roofing in coastal regions?
A – As mentioned above, a site review by the panel manufacturer or paint supplier may be necessary. If the panel supplier does not detail a coastal or marine offer in their literature, probably best to inquire and have the discussion. Some suppliers may approve a reduced warranty on standard painted product for marine locations, but that should always be confirmed in writing.
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