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How to Choose the Right Metal Deck for Low-Slope Roofs

Choosing the right type of roof deck for low-slope roofs makes your construction job easier. The metal deck serves as the structural substrate. Steel roof deck installed directly over structural steel provides the solid surface for weatherproofing, insulation, and roofing materials.

Install metal roof deck on pitched or flat roofs for virtually all types of buildings. Strong, economical, lightweight, and easy to install, steel deck provides a structurally efficient product for roof systems.

Mezzanines and canopies constructed with metal roof deck exposed on the underside give additional visual texture. The corrugated steel profiles provide strength to the structure and an attractive ceiling for the inside.

Types of Roof Deck

Type B Deck

B-deck ranks #1 in popularity in metal deck for new roofs because of its strength/price ratio. Similar to its predecessors, A- and F-, type B decking, also known as wide rib deck, is 1-1/2” deep and 36” wide.

Considered the workhorse of roof deck, B deck also comes in acoustical, cellular, or with both cellular and acoustical properties.

For span tables, contact Keystar.

Type N Deck

N-deck provides a long span structural member for low-slope roofs. At 3” deep and 24” wide, Type N deck meets specifications for structures where the supporting members need to be placed as far apart as possible. This deep deck gives contractors the opportunity to increase the span while decreasing the gauge of the metal.

For span tables, contact Keystar.

Type A Deck

When engineers first developed type A roof decking for low-slope roofs, they focused on the strength of the metal deck. However, it was only a secondary factor of concern. The primary objective was to maximize the width of the top flange. This would provide the maximum amount of support for the roofing insulation installed on top of the Type A deck.

Over time, roofing materials improved and steel deck manufacturers were able to reduce the width of the top flange. This reduction increased the efficiency of the section from Type A decking to Type F decking. And finally, from Type F deck to Type B deck.

Type A decking, also known as narrow rib decking, is 1-1/2” deep and 36” wide. Type A deck usually serves as a patch material for reroofing projects since more economical types of roof deck are now available.

Replacing Type A roof deck in a repair or re-roof application may present some challenges compared to replacing Type B deck. Since the existing, older style narrow rib deck may have a stiffening rib in the top flange, the supports may be spaced farther apart than “modern” Type A decking can span at the same gauge.

Additionally, the old profile of Type A deck is slightly different from the new profile; however, with a bit of encouragement, the two deck styles can be pounded together.

  Type F Deck

After A-deck, engineers developed Type F-deck, also known as intermediate rib decking. Engineers widened the ribs to create a stronger metal roof platform. Eventually, steel deck manufacturers were able to further reduce the width of the top flange, resulting in Type B-deck.

Currently, F deck serves as a patch material for reroofs since more economical types of roof deck are now available. Also measuring 1-1/2” deep and 36” wide.

  An Illustration of Increased Strength

Let’s look at the progress of metal roof deck development for low-slope roofs. In the table below, watch the progression of the maximum spans for the four deck types with the same gauge. For example, notice the differences in these deck types’ span capabilities:


Deck type & gauge Factory Mutual Maximum Spans (Ft-In)
A 20 5’ – 3”
F 20 5’ – 5”
B 20 6’ – 6”
N 20 13’ – 5”

Keystar: Roof Deck Supplier

The wide variety of gauges and lengths of B-deck and N-deck stocked at Keystar guarantees that your construction material needs are met immediately. Painted or galvanized finishes available.

For same day pick up or delivery for patching and repairs, Keystar stocks Type A Deck and Type F Deck in 20 gauge with a painted finish.

Keystar Industries has the inventory of steel decking to provide a timely and professional solution for your construction needs. We provide quality steel deck products to make your construction job easier.

For pricing and availability, call Keystar today at 651-256-0008 or email [email protected].