Type B Roof Deck: The Complete Specs and Buying Guide
If you’ve walked a commercial jobsite in the last few decades, you’ve seen Type B roof deck. It’s the corrugated steel panel sitting between the structure and the insulation on nearly every flat-roofed warehouse, big-box store, and school. At Keystar Industries, we stock, cut, and ship it from our yard in Eagan, Minnesota every single day, so we know exactly why builders keep coming back to it. This guide breaks down the specs, gauges, spans, and finishes you need, then helps you order the right panels the first time.
We’ll keep the technical details honest and the buying advice practical. Whether you’re an architect spec’ing a new building, a GC pricing a re-roof, or a steel erector who just needs panels by tomorrow, you’ll find what you came for here.
What Is Type B Roof Deck?
Type B roof deck is a 1.5 inch B deck, often called the “wide rib” profile. It’s a roll-formed steel panel with deep, evenly spaced ribs that span across roof joists or purlins to create a strong, flat platform. On top of that platform go the insulation boards and the membrane roofing.
It is, by a wide margin, the most common metal roof deck in new commercial and industrial construction in the United States. The reason is simple: it delivers a strong steel roof deck at a low weight and a reasonable price. When you need to cover a lot of square footage on a flat or low-slope roof, Type B is usually the smart default.
The “wide rib” name comes from the shape of the rib openings at the top of the panel. That wide top surface is a practical advantage. It gives insulation boards a broad, stable bearing surface, which makes laying down a roof assembly faster and cleaner.
Type B Roof Deck Specifications
Let’s get into the numbers. The geometry of a wide rib roof deck is standardized enough that you can plan a layout before the panels even arrive. Here are the dimensions we work with on standard B deck.
| Spec | Type B Roof Deck |
| Rib depth | 1.5 inches |
| Profile | Wide rib (“B”) |
| Top rib width | ~2.5 inches |
| Coverage width | 36 inches |
| Overall sheet width | ~39 inches |
| Rib spacing | 6 inches on center |
| Ribs per panel | ~3 |
| Available gauges | 16, 18, 20, 22 |
| Common finishes | Galvanized G60, G90; prime-painted |
The B deck coverage width of 36 inches is the figure to remember for takeoffs. Each panel installs and locks to the next, so three feet of finished roof per sheet is what you estimate against. The extra width on the raw sheet accounts for the side laps.
These dimensions follow Steel Deck Institute (SDI) conventions, which is why a Type B panel from one mill nests and laps cleanly with another. Standardization is one of the quiet reasons this profile dominates the market.
B Deck Gauge: Picking the Right Steel Thickness
Gauge is where most buying decisions actually happen. B deck gauge runs from 16 (the heaviest) to 22 (the lightest), and your choice drives both strength and cost.
- 16 gauge — The thickest and strongest. Used for the heaviest loads and longest spans.
- 18 gauge — A step down, still robust for demanding load conditions.
- 20 gauge — The most common choice. It balances strength, weight, and price for the majority of commercial roofs.
- 22 gauge — The lightest and most economical. A great fit for shorter spans and lighter loads.
If you’re not sure, 20 gauge is the workhorse and the one most projects land on. A thicker gauge buys you longer spans and higher load capacity, but it also adds weight and cost. The right answer comes from your structural engineer’s load and span requirements, and we’re happy to talk through the options when you call.
1.5 B Deck Span: How Far Can It Go?
Span is the distance the deck covers between supports, and it ties directly back to gauge. A heavier gauge spans farther; a lighter gauge needs supports closer together.
For standard 1.5 B deck span in construction conditions, you’re typically looking at a maximum unsupported span up to roughly 6 feet 11 inches, depending on gauge. As a rough rule, a 22 gauge panel handles around a 6-foot span, while heavier gauges stretch farther.
Here’s the key point: these are general construction-span guidelines, not a substitute for engineering. Final spans depend on dead loads, live loads, wind uplift, deflection limits, and your local building code. Always confirm allowable spans against current SDI load tables and your project engineer’s stamp before you order. If you give us the load and span you’re targeting, we can point you to the right gauge.
Finishes: Galvanized G60, G90, and Prime-Painted
Steel rusts. Finish is what stands between your deck and corrosion, so it matters more than buyers sometimes assume.
- Galvanized G60 — A zinc coating suited to indoor or low-moisture environments. A solid, economical default for typical conditioned buildings.
- Galvanized G90 — A heavier zinc coating for outdoor exposure, humidity, or corrosive conditions. Choose this when the deck will see moisture or aggressive air.
- Prime-painted — A painted finish, often used where the underside will be exposed or a specific look is required.
The galvanized coatings are produced to ASTM A653, the standard that governs the zinc coating weight on the steel. When your spec calls out G60 or G90, that’s the document behind it. Match the finish to the environment and you’ll get decades of service.
Type B vs. Type A vs. Type F: How the Profiles Compare
Type B isn’t the only roof deck profile out there. Knowing how it stacks up against the alternatives helps you confirm it’s the right call.
| Profile | Rib Depth | Rib Style | Best For |
| Type A | 1.5 in | Narrow rib | Lighter loads, shorter spans |
| Type F | 1.5 in | Intermediate rib | Mid-range strength needs |
| Type B | 1.5 in | Wide rib | Most commercial roofs; best strength-to-weight |
| Type N | 3 in | Deep rib | Long spans, heavy loads |
Compared to Type A (narrow rib) and Type F (intermediate rib), Type B delivers a higher strength-to-weight ratio, longer spans, and better economy. That combination is exactly why it became the industry standard. Its wide top surface also makes insulation and membrane installation easier than the narrower profiles.
When loads or spans climb beyond what 1.5 inch deck can handle, that’s where Type N comes in. Its 3 inch depth carries heavier loads over longer distances. For most flat and low-slope roofs, though, Type B is the sweet spot. You can compare every profile we stock on our roof deck page.
Where Type B Roof Deck Gets Used
Type B shows up wherever there’s a large, flat, or low-slope roof to cover. We ship it constantly for:
- Warehouses and distribution centers
- Retail centers and big-box stores
- Schools and institutional buildings
- Commercial and office buildings
- Light industrial facilities
The common thread is wide-open roof area that needs an efficient, strong, and economical deck. The wide rib profile speeds up the rest of the roof assembly, because crews can lay insulation boards and membrane roofing across that broad top surface without fighting the panel.
Accessories You’ll Need With B Deck
The deck is only part of the order. A few accessories make the finished roof tight and complete.
- Foam closures (B deck plugs and strips) — These fill the open rib ends to block air, pests, and weather. They’re a small line item that makes a real difference. See our foam closure options.
- Pour stops — Used to contain concrete at deck edges on composite or fill applications.
- Fasteners and trim — The hardware that ties the assembly together.
We carry the full range on our accessories page, so you can complete the whole order in one stop. If your project leans toward a concrete-filled floor system instead of a roof, take a look at our composite deck options too.
Why Buy Your Type B Roof Deck From Keystar
We’re a locally owned and operated metal roof decking supplier based in Eagan, Minnesota. We don’t just resell deck. We stock it, cut it to your order, and get it out the door fast.
Here’s what working with us looks like:
- Made in the USA — Quality steel deck, domestically produced.
- Cut-to-order — We size panels to your layout so you’re not paying for waste or wrestling with field cuts.
- Same-day or next-day — Shipping or pickup, because schedules slip and you need deck now.
- Full product line — Roof deck in types A, B, C, F, and N, plus composite, form deck, accessories, and rentals.
When you call, you talk to people who know decking. That’s the difference between guessing at a gauge and ordering with confidence. Browse everything on our products page or grab our downloadable deck list to spec your job.
Frequently Asked Questions
What is Type B roof deck used for?
Type B roof deck is used as the structural decking on flat and low-slope commercial and industrial roofs. You’ll find it on warehouses, retail centers, schools, and office buildings, where it supports insulation and membrane roofing across long, open spans.
What gauge is best for Type B roof deck?
20 gauge is the most common and the best all-around choice for typical commercial roofs. Heavier gauges (18 and 16) handle longer spans and higher loads, while 22 gauge is the lightest and most economical for shorter spans. Your structural engineer’s load and span requirements should make the final call.
How wide is a Type B roof deck panel?
A standard Type B panel has a 36 inch coverage width, with an overall sheet width of about 39 inches to account for the side laps. Use the 36 inch coverage figure when estimating how many panels your roof needs.
What is the maximum span of 1.5 B deck?
The maximum construction span typically reaches up to about 6 feet 11 inches depending on gauge, with 22 gauge spanning roughly 6 feet. These are general guidelines. Always confirm allowable spans against current SDI load tables and your project engineer before ordering.
What’s the difference between G60 and G90 galvanized B deck?
Both are zinc coatings made to ASTM A653, but G90 is heavier. Use G60 for indoor and low-moisture environments and G90 for outdoor, humid, or corrosive conditions. The heavier coating buys longer-term corrosion protection.
How is Type B different from Type A and Type F deck?
All three are 1.5 inch deep, but they differ in rib shape. Type A has a narrow rib, Type F an intermediate rib, and Type B a wide rib. Type B offers the best strength-to-weight ratio, longer spans, and better economy, which is why it’s the most common choice.
Order Type B Roof Deck From Keystar Today
You know the specs. Now get the deck. We’ll cut your Type B roof deck to order and have it on a truck or ready for pickup as soon as the same day. Call us at (651) 256-0008, request a quote, or contact our team in Eagan, MN. USA-made deck, real experts, fast turnaround. Let’s get your roof covered.
For deeper technical standards, see the Steel Deck Institute, the American Iron and Steel Institute, and ASTM International.