Type N Deck: The 3 Inch Deep Rib Roof Deck Explained

Type N deck is the deepest standard steel roof deck profile. With 3 inch deep ribs, it spans farther between joists and carries heavier roof loads than the 1.5 inch A, F, and B profiles most people picture when they think of metal roof deck. If a set of drawings shows wide joist spacing, big open bays, or a heavy rooftop, there’s a good chance N deck is on the roof plan.

Our team at Keystar Industries supplies N decking along with the full range of roof deck profiles. This guide explains what the 3 inch deep rib profile is, its basic dimensions and gauges, why it spans so well, where it gets used, and how it stacks up against Type A, B, and F deck.

What Is Type N Deck?

Type N roof deck, often shortened to N deck, is a 3 inch deep, wide rib steel deck. The Steel Deck Institute refers to this family as deep rib deck, and you’ll also hear it called 3 inch roof deck or 3DR in some catalogs. The “N” label is shorthand that grew out of older manufacturer naming, just like A, B, and F.

The profile is built for span. Doubling the rib depth of a 1.5 inch deck dramatically increases the sheet’s stiffness, so the same thickness of steel can reach much farther between supports.

Type N Deck Dimensions and Gauges

Exact geometry varies by manufacturer, but N deck generally follows these conventions:

Rib depth: 3 inches.
Rib spacing: 8 inches on center.
Cover width: commonly 24 inches per sheet, with some manufacturers offering other widths such as 32 or 36 inches.
Gauges: typically 22, 20, 18, and 16, with lower numbers meaning thicker steel.
Finishes: galvanized to ASTM A653 (G60 or G90 are common) or prime painted over ASTM A1008 steel, per spec.

Because cover widths differ between N deck and 1.5 inch profiles, your square footage per sheet changes too. Always confirm the cover width of the exact product before finishing a takeoff.

Acoustic N deck

N deck is also available with perforated webs. Filled with acoustic batting, the ribs absorb sound, which is why you’ll see acoustic N deck over gyms, auditoriums, and other loud open spaces.

Why N Decking Spans So Well

Span is where the deep rib deck earns its keep. A few reasons:

Stiffness grows fast with depth. Moving from 1.5 inch to 3 inch ribs greatly increases the section’s resistance to bending, so deflection drops for the same span.
Fewer joists. Longer deck spans mean the engineer can space joists farther apart, which cuts the number of joists, bridging, and connections.
Heavier loads on normal spans. On a typical joist spacing, N deck carries more load than a 1.5 inch profile of the same gauge. That helps on roofs with deep snow drift, ballast, or mechanical equipment.
Diaphragm performance. With the right fastening pattern, N deck can contribute to a strong roof diaphragm. The engineer sets the weld or screw layout and side lap connections.

Actual span limits come from the manufacturer’s load tables for the specific profile, gauge, and span condition. The engineer of record makes the final call on span, gauge, and attachment.

Where Type N Roof Deck Gets Used

N deck shows up wherever roof framing is spread out or roof loads run heavy:

Warehouses and distribution buildings with long joist spacing.
Big box retail and manufacturing plants with wide open bays.
Gyms, arenas, and auditoriums, often with acoustic perforated N deck.
Roofs with heavy equipment, such as rooftop HVAC units or solar arrays.
Snow country roofs where drift loads push beyond what 1.5 inch deck handles comfortably.

It also shows up in re-roofing work when an existing N deck needs replacement sheets that match the original profile.

Type N Deck vs Type A, B and F

Here’s how the 3 inch deep rib profile compares with the three common 1.5 inch roof decks.

Feature	Type A (Narrow Rib)	Type F (Intermediate Rib)	Type B (Wide Rib)	Type N (Deep Rib)
Rib depth	1.5 in	1.5 in	1.5 in	3 in
Rib spacing	6 in on center	6 in on center	6 in on center	8 in on center
Rib opening	Narrow	Intermediate	Wide	Wide
Typical cover width	36 in	36 in	36 in	24 in (other widths available)
Relative span	Shortest	Short	Moderate	Longest
Common gauges	22, 20, 18	22, 20, 18	22, 20, 18, 16	22, 20, 18, 16
Typical use	Older roofs, thin insulation over narrow openings	Repairs and replacement on existing F roofs	Standard commercial roofs	Long spans, heavy loads, open bays

A few takeaways from the table:

A and F deck have narrower rib openings, which older roof systems used to support thin insulation boards. Today they show up mostly in repair and matching work.
B deck is the everyday commercial roof deck, and it’s the profile most N deck projects get compared against.
N deck trades a narrower sheet and more steel per square foot for much longer reach.

For a head to head look at the two most common choices, read our post on B deck vs N deck. If you want the full family side by side, including 1 inch C deck, see our guide to metal roof deck profiles.

Things to Check Before You Spec or Order N Deck

N deck isn’t a drop-in swap for a 1.5 inch profile. Before you order, confirm:

The roof plan calls for it. Changing profiles changes spans, fastening, and roof insulation details, so any substitution needs the engineer’s approval.
Wind uplift and fastening. Roofs designed to FM Global or similar requirements may call for specific attachment patterns.
Insulation above the deck. Board thickness must bridge the rib opening. The roofing manufacturer and guidance from the NRCA help here.
Closures and accessories. Deep ribs need closures sized for the 3 inch profile at walls, edges, and openings.
Cover width in the takeoff. A 24 inch sheet covers less area than a 36 inch sheet, so piece counts go up.

Ordering Type N Deck From Keystar

We cut roof deck to order, including N deck, so sheets arrive at the lengths your joist layout needs. Our Eagan, Minnesota team offers same-day or next-day processing, shipping, or pickup, and the deck we sell is USA-manufactured. Send us the profile, gauge, finish, lengths, and quantities, or a takeoff we can work from. Our N deck supplier page covers sourcing, and the roof deck page shows the full lineup.

Ready to price your roof? Request a quote and we’ll confirm the details with you before anything ships.

Type N Deck FAQ

What is Type N deck?

Type N deck is a 3 inch deep, wide rib steel roof deck. Its deep ribs let it span farther between joists and carry heavier loads than 1.5 inch profiles like Type A, F, and B.

How deep is N deck?

N deck has 3 inch deep ribs, typically spaced 8 inches on center, with a common cover width of 24 inches.

What gauges does N decking come in?

N deck typically comes in 22, 20, 18, and 16 gauge. The engineer of record chooses the gauge based on span, loads, and diaphragm requirements.

When should I use N deck instead of B deck?

N deck makes sense when joists are spaced farther apart or roof loads are heavier than B deck can handle efficiently. The engineer of record should confirm the choice using the manufacturer’s load tables.

Is deep rib deck the same as Type N deck?

Yes. Deep rib deck, 3 inch roof deck, and Type N deck all describe the same basic 3 inch wide rib profile, though exact dimensions vary by manufacturer.