Types of metal roof decking: the ultimate guide (2024)

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Understanding types of Metal Roof Decking

Metal roof decking is the structural surface that spans between supporting members to provide a nailing base for roof coverings like shingles, tiles or metal panels. It transfers live and dead loads to the building’s structural frame. Metal decking offers advantages like being lightweight yet durable, long-lasting and easy to install.

There are different types of metal roof decking profiles available, each designed for specific applications based on load requirements, span lengths and architectural needs. The most common types are A, B, F and N decks which we’ll explore in-depth. But first, let’s define some basic terminology:

Key Takeaways

  • Different types of metal roof decking provides a durable, lightweight, and cost-effective structural base for roofing systems.
  • Common deck types (A, B, F, N) vary in profile shape, depth, gauge, and load-spanning capabilities.
  • Proper deck selection based on factors like roof slope, loads, spans, and project requirements is crucial.
  • Following installation best practices for layout, fastening, edge details, and safety is essential.
  • Qualified professionals can ensure the right deck system is specified for optimal performance.

Deck Depth & Gauge

Deck Depth: Common depths are 1″, 1.5″, 2″ and 3″ but can go up to 7″ for long spans.
Gauge: The thickness of the steel, with lower gauges being thicker and more load-bearing. 18, 20 and 22 gauge are typical for roof decks.

Types of metal roof decking

Type A Metal Deck

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Type A is one of the most commonly used type of metal roof decking. It gets its name from the parallel ridges (“ribs”) running the length of each panel that form a distinct “A-shape” in cross-section.

Key Features

  • Bi-directional spanning capability due to parallel ribs
  • Simple design for easy installaion
  • Common depths: 1.5″, 3″
  • Load spanning up to 10 feet
  • Typical gauges: 18, 20, 22

Type A decks have interlocking side laps that provide lateral load transfer across the width of the deck. This allows for two-way spanning which reduces the number of supporting members needed. Their bi-directional strength makes them ideal for re-roofing over existing decks.

Installation Tip: Use proper side lap attachment along each rib and avoid over-driving deck screws which can damage the interlocking lips.

Type B Metal Deck

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Also known as “wide rib” or “bowl shaped” decks, Type B roof decking has deeper, wider spaced parallel ribs designed to support extra-long spans and heavier load conditions.

Key Features

  • Longer spanning 20′ up to 40’+ feet
  • Handles roof loads from equipment, machinery, etc.
  • Deeper profile depths of 3″ or more
  • Lightweight yet extremely rigid

The wider fluted profile and heftier 16-18 gauge steel makes Type B ideally suited for commercial or industrial roofing. Some configurations incorporate a cellular or acoustic design which provides superior insulation and noise reduction properties.

“Type B metal deck lets us economically frame industrial buildings with much longer unobstructed spans compared to open web steel joists or other methods.”Jason R., Project Manager for Spanco Building Systems

Type F Metal Deck

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Type F deck, also called a “fluted” or “indented” deck, gets its name from the distinct parallel grooves or flutes pressed into each wide panel. This unique profile lends itself well to re-roofing applications over existing flat roofs.

Key Features

  • Inherent insulation space between flutes to add rigid boards
  • Raised flutes provide venting/moisture control
  • Overlapping sidelap joints create solid substrates
  • Common depths of 1.5″ and 3″

Type F deck can be installed directly over the old roof system to create an elevated insulation/venting cavity above. Rigid insulation boards fit snugly into the underside flutes.

Installation Tips: Use telescoping fasteners into structural members and Properly lap joints as specified with offsets. Make design for sufficient roof slope and drainage.

Type N Metal Roof Decking

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N-Decks feature narrower, taller parallel ribs standing up to 3 inches high for increased strength and rigidity. This “narrow rib” style of metal deck is lightweight yet robust enough to span open areas up to 12 feet.

Key Features

  • Very economical use of materials
  • Simple installation for large open areas
  • Higher ribs ideal for concrete fill applications
  • Spans beyond 10 feet require heavier gauges

While not as heavy-duty as wide rib type B, N-deck provides versatility for many typical roof specifications. Other types of metal roof decking include cellular decks for added insulation, vented decks for breathing roofs and acoustic styles with fillers for dampening sound. The options are designed to meet a huge variety of project requirements.

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Comparing Deck Depths and Gauges

Once you’ve evaluated the different types of metal roof deck profiles for your building type and performance needs, the next step is to determine the proper depth and gauge for load-bearing demands and spanning.

As covered earlier, common depths include:

  • 1 inch
  • 1.5 inch
  • 2 inch
  • 3 inch

With steel roof deck, thethickness (gauge) correlates directly to the load-spanning abilityas well as cost. Typical gauges for roof construction are:

18 gauge– Heavy-duty, high loads/long spans up to 30+ feet
20 gauge– Moderate loads and spans around 10-25 feet22 gauge– Light loads, shorter spans less than 10 feet

The deeper and thicker the deck, the more it can span between supports while carrying heavy live and dead loads like snowdrifts, equipment or covering materials. This has to be balanced against the cost-efficiency for the specific project requirements.

For example, an open bullpen office may only need lighter 1.5 inch 20ga decking to span 10-12 feet between bar joists. But an industrial facility supporting heavy machinery would likely need 18ga 3 inch Type B deck for 25+ foot spans.

DepthTypical GaugeMax Span
1″20ga – 22ga5′ – 8′
1.5″18ga – 20ga8′ – 12′
2″18ga12′ – 16′
3″16ga – 18ga16′- 30’+

There are software and deck calculators available to determine precise load ratings and spans based on codes and safety factors. Always consult structural drawings, follow manufacturer specifications and check local building requirements.

How to Choose the Right type of Metal Roof Decking

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With such types of metal roof decking materials, depths and profiles available, selecting the proper type for your roofing project is crucial to meeting all performance, load and span requirements.

Some key factors to consider include:

Roof Slope: Low-slope (1/4:12 or less) roofs typically use Type F fluted deck for insulation/re-roofing. Steeper sloped roofs utilize A, B or N decks.

Concentrated Loads: Equipment, storage areas or foot traffic demands stronger B or N deck able to handle point/line loads.

Overall Span: Simple spans under 10′ could use lighter 1″ A or N deck, but longer spans over 25′ require deeper 3″+ B deck.

Substrate Conditions: Re-roofing over existing roofs/decks may influence using Type F fluted style.

Ventilation/Insulation Needs: Cavity designs like cellular, composite or vented deck for air/moisture control.

Fire/Acoustic Ratings: Some decks made for additional fire protection or noise-dampening.

Deck Material: Most use galvanized, galvalume or painted steel, but aluminum may be required in some applications.

Many times, a combination of different deck profiles and depths will be used across different roof areas. It all depends on the specific building design, support conditions and desired characteristics.

Conclusions

Different types of Metal roof decking offers an extremely versatile, durable and efficient structural solution for roofing projects of any type or size.

With various profiles like Type A, B, F and N decks available in different depths and gauges, there is a configuration to meet virtually any load, span and performance requirement.

The key is properly evaluating all the factors for your specific project needs. This includes considering roof slopes, concentrated loads, open span distances, ventilation, acoustics, fire ratings and more.

Taking the time upfront to choose the right metal deck type pays dividends in safety, structural integrity and longevity down the road.

FAQ’s

What is the difference between metal deck types?

The main types (A, B, F, N) differ in their rib configurations, allowable spans, load capacities, and intended applications (e.g., Type F for re-roofing).

How do I determine the right deck depth and gauge?

Deeper decks (3″ vs. 1.5″) and lower gauges (18ga vs. 22ga) provide greater load-spanning abilities but at higher costs. Evaluate span requirements and expected loads.

Can metal decking be used for both roofs and floors?

Yes, metal deck profiles are available for roof and floor applications, with some types like cellular decks designed specifically for each use.

What are the advantages of metal decking over alternatives?

Key benefits include being lightweight yet strong, non-combustible, long-lasting, quick installation, and relatively low cost compared to poured concrete or open-web joists.

How important is proper fastening and attachment?

Extremely important – the mechanical fasteners transfer all live/dead loads to the support framing. Following specified screw patterns, weld spacing, etc. is critical for safety.

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