Type A Deck: The Narrow Rib Steel Roof Deck Profile Explained
When a roofing spec calls for a Type A deck, it points to one specific shape of steel roof decking: the narrow rib profile. At Keystar Industries, we stock and cut steel roof deck every day, and the Type A deck is one of the profiles people ask us to match when a project drawing names it directly. This guide walks through what a Type A roof deck is, how its narrow rib differs from the wide rib and intermediate rib profiles, the gauges and coatings we supply, and where this deck earns its place on a commercial roof.
We’re a locally owned and operated supplier in Eagan, Minnesota. We ship USA-made steel deck same-day or next-day, cut-to-order, so the practical details below come straight from the yard, not a brochure.
What Is a Type A Deck?
A Type A roof deck is a corrugated steel roofing panel with a narrow rib opening at the top of each flute. Like the rest of the standard 1.5″ roof deck family, it runs 1.5 inches deep with 36 inches of net coverage per sheet. What sets it apart is the width of the rib opening across the top surface.
On a Type A deck, the top flutes are narrower than they are on a Type B (wide rib) or Type F (intermediate rib) deck. Squeeze the rib opening narrower at the top, and you get more flat steel bearing area across the top surface of the panel. That extra top-surface steel is the whole point of the profile, and it’s why some roofing systems specifically call for it.
In short, the A deck is a structural steel base. It spans the joists or purlins, then carries rigid insulation and a membrane on top. The roof loads transfer down through the deck into the building’s structure, the same job every roof deck profile performs. The narrow rib just changes the surface those upper layers sit on.
You’ll find the full lineup of profiles, including the A deck, on our roof deck page.
Type A vs. Type F vs. Type B: The Rib-Width Family
Steel roof decks in the 1.5″ family share the same depth and coverage. They’re sorted by how wide the rib opening sits at the top of the panel. That single dimension defines the family:
- Type A — narrow rib. The tightest top flute, the most top-surface steel.
- Type F — intermediate rib. A middle-ground opening between A and B.
- Type B — wide rib. The widest top flute and the most common deck on the market today.
Picture the same panel three times, each one with a different-width slot stamped along the top. Narrow, medium, wide. That progression from A to F to B is the easiest way to keep the three straight.
| Profile | Rib type | Depth | Coverage | Top rib opening | How common |
| Type A | Narrow rib | 1.5 in | 36 in | Narrowest | Less common; specified on purpose |
| Type F | Intermediate rib | 1.5 in | 36 in | Medium | Moderate |
| Type B | Wide rib | 1.5 in | 36 in | Widest | Most common |
Because the three profiles look similar at a glance, matching the exact one on your drawings matters. A panel that’s close but not correct can change how insulation boards bear and how a membrane fastens. When a print says Type A, we supply Type A. For a side-by-side look at the wide rib profile, see our dedicated roof deck page, where we break down each option.
Why a Narrow Rib at All?
The narrow rib pattern delivers a more continuous run of steel across the top of the panel. That broader bearing surface supports certain roofing assemblies well, particularly some adhered and mechanically attached membrane systems and some rigid insulation layouts where the insulation board benefits from sitting on more steel and less open flute.
Type B’s wide rib is popular because it’s economical and works for the majority of jobs. But “most common” isn’t the same as “right for every job.” When a designer wants the narrow rib bearing pattern, the narrow ribbed roof deck is the correct call, and that’s exactly when the A deck gets specified.
Type A Deck Specifications and Gauges
Here’s what we carry and what to confirm before you order. The Steel Deck Institute publishes the design standards these profiles follow, and the dimensions stay consistent across manufacturers.
Core dimensions
- Depth:5 inches
- Coverage: 36 inches net per sheet
- Profile: Narrow rib (Type A)
Available gauges
- 22 gauge — lightest, shorter spans
- 20 gauge
- 18 gauge
- 16 gauge — heaviest, longest spans and higher loads
Gauge selection comes down to span and load. Longer distances between supports and heavier roof loads push you toward a thicker (lower-number) gauge. If you’re not sure which gauge your spans require, send us the layout and we’ll help you land on the right one.
| Specification | Type A Deck |
| Rib profile | Narrow rib |
| Depth | 1.5 in |
| Coverage width | 36 in |
| Gauges | 22, 20, 18, 16 |
| Coatings | Galvanized G60, G90; painted |
| Standards | SDI; ASTM A653 (galvanized) |
Coatings: G60, G90, and Painted
Steel roof deck needs a coating to resist corrosion, and the right one depends on the environment.
- Galvanized G60 suits indoor, dry, conditioned spaces where moisture exposure is low.
- Galvanized G90 carries a heavier zinc coating for outdoor or corrosive conditions where the deck faces more moisture or aggressive air.
- Painted finishes are also available when a project calls for them.
Our galvanized steel roof deck meets ASTM International standard A653 for zinc-coated steel sheet. When you tell us the environment, we’ll point you to G60 or G90 so the deck holds up for the life of the roof.
Where Type A Deck Gets Used
The 1.5 inch roof deck in narrow rib form does the same structural job as its siblings: it’s the load-bearing base of a low-slope or flat commercial roof. You’ll see it on:
- Commercial buildings
- Industrial facilities and warehouses
- Other flat and low-slope roof structures
In a typical assembly, the deck spans the structural framing, rigid insulation goes down on top, and a membrane finishes the system. The Type A’s narrow rib gives that insulation-and-membrane layer the broader steel bearing surface some assemblies prefer.
To finish the job cleanly, pair the deck with the right accessories and seal the flutes at terminations and transitions with foam closure strips. Those small parts keep air, pests, and weather out of the ribs. Browse the full product lineup to round out an order.
Is Type A the Right Deck for Your Project?
Honestly, for a lot of roofs, Type B wide rib is the default, and there’s nothing wrong with that. But the answer should come from your drawings and your roofing system, not from whatever’s most common.
Use Type A roof deck when:
- Your construction documents specifically call out Type A or a narrow rib profile.
- Your membrane or insulation system performs better on a narrow rib bearing pattern.
- You’re matching an existing deck on a re-roof or addition.
If your specs name a different profile, match that instead. We supply the narrow rib, intermediate rib, wide rib, deep rib, and more, so we’ll fit your project either way. Not sure what you’re looking at? Send us a photo or a section detail. After years of cutting and shipping steel deck across the region, we can usually identify a profile fast and confirm the gauge and coating you need.
Why Buy Type A Deck From Keystar
Getting the profile right is only half the order. The other half is having it on hand and out the door when your crew needs it. Here’s what we bring to the table.
- We match the profile. Type A means Type A. We don’t substitute a wide rib and hope it works.
- Cut-to-order. We cut your deck to length so sheets show up ready to lay.
- Same-day or next-day. Ship or pick up fast from our Eagan, MN yard. Roof schedules don’t wait, and neither do we.
- USA-made steel. Domestic deck, manufactured to recognized standards.
- Expert help. Talk to people who handle this product daily and can answer profile, gauge, and coating questions on the spot.
The American steel that goes into our deck is produced to the standards championed by the American Iron and Steel Institute, and the deck profiles themselves follow the engineering guidance of the Steel Deck Institute. That combination is what “USA-made and built to spec” actually means.
Want the full catalog in hand? Download our deck list and keep it for your next bid.
Frequently Asked Questions
What is a Type A deck?
A Type A deck is a steel roof decking panel with a narrow rib profile. It’s 1.5 inches deep with 36 inches of coverage, like other standard roof decks, but its top rib openings are narrower than Type B or Type F. That narrow rib gives more top-surface steel bearing area for certain roofing and insulation systems.
What’s the difference between Type A and Type B deck?
The difference is the rib opening at the top of the panel. Type A is the narrow rib profile, and Type B is the wide rib profile, which is the most common deck today. Both are 1.5 inches deep with 36 inches of coverage. Type A’s narrower top flute leaves more flat steel across the surface, which suits assemblies that benefit from a broader bearing area.
What gauges does Type A roof deck come in?
We supply Type A roof deck in 22, 20, 18, and 16 gauge. Lighter gauges (higher numbers) work for shorter spans and lighter loads, while heavier gauges (lower numbers) handle longer spans and higher loads. If you share your span layout, we’ll help you choose.
Should I use G60 or G90 coating?
Use galvanized G60 for indoor, dry, conditioned spaces with low moisture. Use G90 for outdoor or corrosive environments where the deck faces more moisture or aggressive conditions. Painted finishes are also available. Both galvanized coatings meet ASTM A653.
Is Type A deck still used today?
Yes, though it’s less common than Type B wide rib deck. Type A gets specified where the narrow rib pattern is preferred for the roofing or insulation system, or where a re-roof needs to match an existing deck. When your drawings call for it, we stock and cut it.
Can Keystar ship Type A deck quickly?
Yes. We offer same-day or next-day shipping and pickup from our Eagan, Minnesota location, and we cut deck to order so it arrives ready to install. Call us or request a quote and we’ll confirm availability for your gauge and coating.
Get a Quote on Type A Deck Today
Need narrow rib roof deck cut to your lengths and out the door fast? We’ve got the profiles, the gauges, and the coatings, all USA-made and ready to ship. Tell us your specs and we’ll match them exactly.
Request a quote or call us at (651) 256-0008. You can also contact our team with questions about profile matching, gauges, or coatings, and we’ll get you squared away.