Aluminum vs Steel Roofing in Salt Air: Which Actually Lasts?

Is steel roofing a poor choice for Washington homes?

No, and it would be dishonest to say so. Steel is a capable roofing metal and for many Washington houses a sensible one. It is stiffer than aluminum, it holds a crisp formed profile, it generally costs less per square, and away from saltwater a properly coated steel roof has a long and uneventful life. The case made on this page is narrower than material against material. It turns on one variable: chloride exposure. Change that variable and the ranking changes with it. A homeowner in Enumclaw and a homeowner on Bellingham Bay are not answering the same question. It is also worth naming how the two metals differ mechanically. Steel corrodes when its protective system is breached. Aluminum does not have that failure mode, but it is a softer metal, so it has to be engineered differently. Interlock panels take their stiffness from a formed profile and a four-sided interlock rather than from sheet thickness alone.

How do galvanized, Galvalume and stone-coated steel differ?

Galvanized steel is carbon steel with a zinc coating. Zinc protects twice over: it is a physical barrier, and it is sacrificial, so where the coating is scratched the zinc corrodes in preference to the steel and shields the exposed edge for a short distance. In a chloride environment that sacrificial reserve is consumed faster than it is inland. Galvalume is steel coated with an aluminum-zinc alloy, roughly 55 percent aluminum by weight. It generally outperforms plain galvanized across flat surfaces because the aluminum component slows the barrier from breaking down, but it provides less sacrificial protection at a cut edge than zinc does. Manufacturers commonly note reduced coastal performance, and warranty language often reflects that. Stone-coated steel adds an acrylic-bonded stone granule layer over a Galvalume substrate. The granules provide texture and color and they shield the coating from ultraviolet light, which is a genuine benefit. They are not a corrosion barrier for the cut edge underneath. When a stone-coated panel is trimmed on site, the steel core is exposed exactly as it would be on a bare panel. None of this makes steel a poor product. It makes coating integrity the thing that determines its service life, and salt air is the environment that tests coating integrity hardest.

What is the argument for aluminum in salt air?

Aluminum removes the variable. There is no iron to oxidize, so the condition of a coating at a cut edge does not determine corrosion behavior. Aluminum forms its own oxide film continuously, including across freshly cut or scratched surfaces, and that film is the corrosion protection. Interlock uses ASTM B209 aluminum in 3105-H24 or 3003-H24 temper with roughly 95 percent recycled content, finished in an AAMA 2605 70 percent PVDF Alunar coating warranted for 30 years. Panels interlock on all four sides with concealed fasteners, which removes exposed screw heads and rubber gaskets from the weather side of the roof entirely. The system holds ICC-ES ESR-1790, which reports wind uplift resistance to 177.5 psf, and UL 2218 Class 4 impact, the most severe of the four UL 2218 test levels. A Class A fire rating is available depending on the assembly specified. Aluminum is also light, which matters on older shoreline homes where existing framing capacity is a real question.

Which lasts longer on a Washington shoreline?

Aluminum, and the reason is structural rather than promotional. On a shoreline roof the clock usually starts at a cut edge or a fastener penetration. Coated steel has that clock running from the day the panels are trimmed. Aluminum does not. That gap narrows sharply once you move inland. In the Cascade foothills or east of the crest, where chloride loading is negligible, a Galvalume or stone-coated steel roof competes on its own terms and the practical difference between the two metals is much smaller. There the deciding factors are usually weight, appearance, fastener design, impact resistance and what the warranty actually covers. The honest summary: on the Salish Sea, the Strait of Juan de Fuca, and the Kitsap and Hood Canal shorelines, choose the metal that has no iron in it. Inland, weigh cost, appearance, structure and warranty, and steel deserves a fair hearing.

What should you ask a contractor about either material?

Ask what the base metal is, in plain terms, and what the corrosion protection actually is. If the answer is a coating, ask what happens where the coating is cut. Ask to see the detail the crew uses at hips, valleys and rakes, since those are the locations where a coastal steel roof is tested first. Ask whether fasteners are exposed or concealed. Exposed-fastener panels are faster to install and cheaper, and they put a rubber gasket and a screw head in the weather at every fixing point. Concealed-fastener systems cost more to install and remove that exposure. Finally, ask for the material warranty document itself rather than a summary sheet, and read the exclusions. A warranty that limits or voids coverage within a stated distance of saltwater is telling you something specific about how the manufacturer expects the product to perform on your street.

Common questions