Galvanized and Galvalume are both corrosion-resistant coatings for steel, and buyers hear both terms thrown around like they mean the same thing. They don't. Galvanized is a zinc coating. Galvalume is an aluminum-zinc coating. They protect steel differently, and they get applied differently. On a real steel building, they end up on different parts for real reasons, not by accident.

Here's which coating does which job, which one goes where on a Northcraft building, and what that means if you're comparing quotes.

What each coating actually is

Galvanized steel is coated in zinc, most commonly by hot-dip galvanizing: a finished steel piece is dipped in a bath of molten zinc. That bath bonds to the surface and covers it completely, including corners and edges a spray or roll coating would miss. Zinc protects the steel underneath even where the coating gets scratched, because zinc corrodes sacrificially before the bare steel does. It's an old, well-proven process, and it's the right one for heavy, already-fabricated steel shapes.

Galvalume is a different coating entirely: a mix of aluminum and zinc, applied to flat sheet steel at the mill. That happens before the sheet is ever cut, drilled, or roll-formed into anything. The aluminum forms a stable barrier that resists corrosion on its own. The zinc in the mix still gives some of that same sacrificial protection at cut edges and scratches. It's a common coating for the lighter, formed steel that makes up secondary framing like girts and purlins.

Which parts of a Northcraft building get which coating

Northcraft's I-beam main frames are finished with a gray primer, the industry standard for heavy, hot-rolled structural steel that is welded and fabricated into finished frame sections. If a project calls for more, hot-dip galvanized I-beam frames are available on request. That is the kind of steel hot-dip galvanizing is built for: the finished sections are dipped as complete pieces, and a kettle big enough to submerge a structural member coats it top to bottom in one pass.

All girts and purlins are coated in Galvalume AZ55. Those are the lighter, roll-formed secondary framing members that run between the main frames. They start out as flat coated sheet steel before they're ever formed into shape. Girts and purlins typically run a few feet apart across the wall and roof. A real amount of surface area depends on that coating holding up for decades, much of it facing the insulation and the inside of the building, where nobody is looking at it.

So on a standard Northcraft building, Galvalume coats the girts, purlins and panels, and the I-beam main frames get gray primer, with hot-dip galvanized frames only if you ask for them. Each part is finished the way that actually suits it.

Cut edges are where a coating gets tested

Every coated steel component gets cut, drilled, or trimmed somewhere during fabrication. A plain painted edge with no metallic coating underneath is bare steel the moment that happens. This is the real advantage both galvanized and Galvalume have over paint alone: each protects a cut edge or scratch to some degree even after the coating itself is broken. How well depends on the coating, the size of the cut, and the environment, so ask how fabrication damage and exposed edges are actually treated. A supplier who can't explain what happens at a cut edge probably hasn't thought about it either.

The paint on top

Northcraft's roof and wall panels are coated in Galvalume AZ55, the same coating as the girts and purlins. When you compare quotes, ask every supplier what metallic coating and paint system are specified for the wall and roof panels, and get it in writing. That combination is what gives the building its color and determines how well it keeps protecting the steel underneath if the paint eventually chips or fades from hail, a ladder, or years of weather. See our full breakdown of baked-on paint versus powder coating for how that paint system compares to the alternatives, including why powder coating alone is a different product entirely.

Why a "galvanized shed" at the farm store is a different product

A lot of buyers see "galvanized" advertised on a small storage shed or a carport frame. They assume it means the same corrosion protection as a real steel building. Usually it doesn't, because the framing itself is a different category: thin tube steel, connected with brackets and self-tapping screws instead of structural bolts. Its thin tube framing and connection details differ from a solid-frame steel building. The coating name on the tag is not the whole story. What the steel is shaped like, and how thick it actually is, matters as much as what it's coated with. Our frame types comparison covers where tube steel may suit a smaller structure and where a solid frame is appropriate, and where it isn't enough building for the job.

What to ask a supplier

If you're comparing quotes, get specific answers to these before you sign anything:

  • Which coating is on the main frame, and which is on the secondary framing (girts and purlins)?
  • How are cut edges and drilled holes protected during fabrication, not just the flat panel surface?
  • What does the written warranty document actually say, in years and in exclusions, not just what the salesperson tells you verbally?
  • Is the coating applied at the mill before fabrication, or after, in the field?

Northcraft backs its coated steel with the 50-Year Rust Perforation Warranty. Ask any supplier to put their coating and warranty answers on paper, and compare that document, not the sales pitch. Our guide to steel building hardware covers the same kind of question for fasteners. They corrode at their own rate if they're the wrong material for the panel they're holding.

Frequently asked questions

Is Galvalume better than galvanized?

Neither one is categorically better in every environment. Compare the specified coating, exposed-edge details, warranty exclusions and the conditions at your site instead of assuming one wins everywhere. The aluminum in Galvalume generally forms a stable long-term barrier, but check the manufacturer's written restrictions for coastal, agricultural and industrial environments, since performance depends on the exact exposure. That doesn't make plain galvanized coating bad. It means the two coatings suit different products, so ask what's specified and why. See our article on how long steel buildings last for how coating choice affects service life overall.

Why aren't the main frames Galvalume?

Because they're a different kind of steel altogether: heavy, hot-rolled structural sections, fabricated into finished frame pieces first. Galvalume is a mill coating for flat sheet steel, which isn't what an I-beam frame is made from. Northcraft finishes its I-beam frames with a gray primer, the industry standard, and hot-dip galvanized frames are available on request.

Will a galvanized shed rust?

Eventually, like any coated steel, once the coating is compromised. How fast depends on the coating thickness, the steel gauge underneath it, the climate, and how well cut edges and fasteners were protected during fabrication. Compare those specifics, plus connection details, drainage and warranty exclusions, rather than predicting corrosion from the frame shape alone. Ask any supplier, tube-frame or solid-frame, what coating is specified on the panels and framing, and get it in writing.

Can you paint over Galvalume?

Yes, and that's exactly how most Galvalume-coated panels are finished: a baked-on paint system applied over the Galvalume substrate at the mill. It's not applied after the fact, in the field. The paint gives you color and UV protection. The Galvalume underneath keeps doing the corrosion-protection job even if the paint is scratched.

How long does Galvalume last?

It depends heavily on climate. Milder inland environments generally see the longest service life. Coastal or heavily industrial environments tend to wear out sooner. Ask your supplier for the specific written warranty document rather than a verbal estimate, since that document is what actually holds them to an answer.

Tell us what you're comparing, and an estimator will walk you through exactly what's coated with what on a Northcraft building. Start a quote.