Washington · Steel vs aluminum
Steel vs aluminum roofing
A steel roof is protected from rust by its zinc or aluminum-zinc coating and paint, and lasts as long as they do. An aluminum roof has no steel to rust: its oxide film protects it, and it weighs about a third as much. Steel usually costs less up front; aluminum is the longer-lived choice.
Reviewed by Scott Plumptree, Director of Marketing, The Interlock Group · Updated October 7, 2026
Steel
Protected by its coating
Galvanized (zinc) or Galvalume (aluminum-zinc).
Aluminum
Protected by the metal itself
An oxide film blocks further oxidation.
Weight
Aluminum ≈ one-third of steel
By density, ASM International.
Side by side
| Steel roofing | Aluminum roofing | |
|---|---|---|
| What keeps it from corroding | A metallic coating, zinc (galvanized) or aluminum-zinc (Galvalume), under the paint | The aluminum itself: its oxide film blocks further oxidation |
| If the finish is scratched or cut | The steel is protected only as long as the coating around it lasts; galvanized cut edges are bare steel once the zinc nearby is used up | Bare aluminum forms the same oxide film; there is no steel to rust |
| Weight | Heavier | About one-third the density of steel |
| Dents | Thicker steel resists denting better than thin aluminum | Can dent under large hail or foot traffic; dents are cosmetic and usually excluded from warranties |
| Up-front price | Usually lower | Usually higher |
| Things to avoid | Galvalume corrodes quickly in contact with wet mortar or concrete, and should not take run-off from copper | Keep it out of direct contact with dissimilar metals; flashings are matched to the system |
| Typical buyer | Lowest up-front cost, dry inland site | Longest-lived option; salt air on the water, or firs and cedars that keep a roof damp |
Steel: ArcelorMittal Dofasco (Galvalume product information) and Gibraltar Building Products. Aluminum: ASM International. References at the end of the page.
Aluminum roofs in Washington
Recent Interlock® roofs installed in Washington by our own company. Tap a roof to see all of its photos.
Why most metal roofers sell steel
Steel coil is widely available and costs less, so most metal roofing sold is steel: painted steel tile, steel shingles and steel panels. A good steel roof, well installed, is a sound roof. Its life depends on its metallic coating and paint, which is why steel warranties are written in years.
We install aluminum because it takes the coating question off the table. An Interlock® panel has no steel in it, so a scratch, a cut edge or a fastener hole has nothing to rust.
Questions that settle it for your house
- How long do you plan to own the home? The longer you stay, the more a roof you never replace is worth.
- Is the house on Puget Sound, Hood Canal or the coast, or under firs and cedars that keep the roof damp through the wet season?
- Do you want a slate, cedar or tile look, or plain panels? Profiles differ more than metals.
- Who is the warrantor, the manufacturer or the contractor, and what does the material warranty cover after year ten?
- Are the fasteners concealed or screwed through the face?
Questions, answered
Is steel or aluminum better for a roof in Washington?
Both make good roofs. Steel costs less up front and depends on its zinc or aluminum-zinc coating to keep from rusting. Aluminum doesn't rust and is about a third the weight. For a house you'll keep, in salt air on the water or under trees that keep a roof damp for months, aluminum is the longer-lived choice.
Does a steel roof rust?
Steel itself rusts; a steel roof is protected by its metallic coating and paint. Where the coating is cut, scratched or used up, as at galvanized cut edges over time, rust can start.
Does an aluminum roof rust?
No. Aluminum forms an oxide film that blocks further oxidation, and there is no steel in an aluminum roof to rust.
Is aluminum roofing more expensive than steel?
Usually, yes, up front. You get a written price for an Interlock® aluminum roof after your roof consultation, which is free, so you can compare it with a steel quote line by line.
Is steel roofing stronger than aluminum?
Steel is stronger and stiffer for the same thickness, which is why it resists denting better. Aluminum is lighter. On a roof deck, both carry snow load through the structure underneath; strength of the panel matters most for dents.
Who installs aluminum roofing instead of steel in Washington?
Interlock Metal Roofing (PNW) Inc. installs the Interlock® aluminum roofing system from our Seattle, Bellingham and Stanwood offices, with 3,219 roofs completed in Washington since 1997. Call (206) 589-8423.
Sources
- ArcelorMittal Dofasco: Galvalume™ steel sheet, product information
- Gibraltar Building Products: why are the edges of my painted galvanized roof rusting?
- J.R. Davis, "Aluminum and Aluminum Alloys", Alloying: Understanding the Basics, ASM International (2001)
- Interlock Roofing: aluminum shingles, technical specifications
Product specifications are the manufacturer's (Interlock Roofing). Install counts are from our own job book. Reviewed by Scott Plumptree, October 7, 2026.
Compare an aluminum quote with your steel quote.
A written price after your roof consultation, at your home or on Zoom. Interlock Metal Roofing (PNW) Inc. · 5608 17th Ave NW, Suite 1574, Seattle, WA 98107-5232 · 2219 Rimland Dr, Suite 301, Bellingham, WA 98226-8660 · 26910 92nd Ave NW, Suite 425, Stanwood, WA 98292
