Introduction
Metal roof decking provides the stable surface that low-slope roof assemblies are built upon in commercial projects. This corrugated steel sheeting offers durability, strength, fire protection, and support for roof loads.
In this comprehensive guide, we’ll explore metal deck components, types, purposes, finishes and more in detail.
Key Takeaways
What is Metal Roof Decking?
Metal roof decking refers to structural, cold-formed steel panels configured in repeating patterns of raised ribs and recessed valleys.
- Serve as a stable working platform for roofing installers
- Provide a solid base for attaching roof insulation and membranes
- Transfer dead, live, wind, and other loads to structural supports
With panel lengths up to 60 feet and shop-applied coatings, metal deck delivers an efficient, lightweight solution for mezzanines, canopies, and multi-story buildings.
Other Common Terminology:
Types and Uses of Metal Roof Deck
There are two main categories of metal decking, each with distinct installation methods and functions:
Structural Metal Roof Deck
This type of deck is installed atop steel bar joists, beams, or open web steel joists to create a surface for attaching the roof system. The ribs of the deck can span several feet between the structural members below. Common applications include:
- Mezzanine decks
- Equipment platforms
- Steel canopies
- Sloped metal roofs
| Labels | Description |
|---|---|
| Installation Method | Over structural steel bar joists or wide flange beams |
| Main Purpose | Platform for built-up roofing system |
| Typical Applications | Mezzanine decks, equipment platforms, steel canopies, sloped roofs |
Structural metal roof deck is an ideal solution for exposed structural applications requiring weatherproofing integrity over occupied spaces below.
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Composite Floor Deck
Composite floor deck serves as the base for a structural concrete slab system. It is installed over steel framing members and has embossments to mechanically bond with the concrete once cured. Common applications include:
| Labels | Description |
|---|---|
| Installation Method | Over steel bar joists and beams |
| Main Purpose | Reinforced concrete floor system with metal deck |
| Typical Applications | Elevated slabs, mezzanine decks, working platforms |
The composite floor deck acts as part of the reinforcing system in the concrete slab, boosting strength and section properties. This translates to longer spans between beams and lighter sections compared to placing concrete over form deck.
Profiles and Selection Factors
There are over a dozen specific metal deck profiles available from quality deck manufacturers, ranging from 1-1/2 inches deep all the way up to 7-1/2 inches. Each style has calculated load tables and maximum span capabilities. Some common types include:
N Deck – 3-inch deep fluted deck, most commonly used due to optimal balance of strength and economy.
B Deck – 1 1/2-inch fluted deck, lowest cost profile, sufficient for shorter spans.
F Deck – 3-inch deep fluted deck with a flat bottom pan for acoustic control. Allows passage of mechanical systems without interfering with structure above.
A Deck – 1-inch deep fluted deck for tight interstitial spaces. Not suitable for roof construction.
H Panel Deck – Structural composite floor deck with slots along bottom plate to facilitate mechanical bonding and shear stud placement.
In selecting the optimal deck profile, key factors include:
Purpose and Structural Function
As a base structural component, metal roof decking provides:
Gravity Support
- Transfers superimposed dead loads (self-weight, mechanical equipment)
- Transfers live loads (rain, snow, suspended ceilings, foot traffic)
- Resists negative wind pressure via deck attachment and continuity
Lateral Strength
- Wind and seismic horizontal force resistance
- Ties the steel framing together by acting as a diaphragm
- Shear transfer to braced bays
Important Metal Roof Deck Specifications
Specifying the optimal metal roof decking for your project involves analyzing:
Span Capabilities
The maximum spacing between roof deck supports varies based on factors like material gauge, deck profile, design loads, and fastener type. Most profiles can safely span 4-5 feet with heavier gauges reaching up to 7 feet.
Fire Ratings
Listings provide 1-2 hour fire resistance ratings when properly tested and classified. This data guides approval for use in fire-rated roof assemblies.
Minimum Slopes
A minimum 1/4 inch per foot slope allows proper drainage on metal decks. Special tapered panels can be used to create more slope.
Wind Uplift Resistance
Wind forces must be counteracted by specifying the right deck attachment method whether welds, screws, or clips.
Integration With Other Systems
Decking layout coordinates with ducts, piping, conduit, equipment curbs, and roof penetrations.
Vapor Retarders
A vapor control layer is usually installed above the roof deck and below insulation.
Code Compliance
The decking specification must comply with IBC, ASCE 7, and FM Global standards for wind, seismic, live loads, and fire protection. Partnering with an experienced metal decking manufacturer is invaluable to analyze all design factors and ensure your project’s success.
What’s Included in a Metal Roof Decking Assembly?
A typical non-ballasted commercial roof deck assembly consists of:
1. Metal Roof Deck – Corrugated steel sheets with repeating raised ribs, installed atop steel bar joists or open web steel joists.
2. Rigid Insulation – Polyisocyanurate or polystyrene boards serving as the thermal barrier and moisture protection layer.
3. Roof Membrane – Hot asphalt, torched-down, fully adhered or mechanically fastened membranes that waterproof the roof surface. Thermoplastic polyolefin (TPO) and polyvinyl chloride (PVC) membranes are also options.
4. Other Components – Cant strips at wall transitions, sleeper blocks to serve as insulation anchors, pitch pans for roof penetrations passing through the waterproofing layer. Perimeter nailers secure membrane edges and provide attachment points for metal flashings.
The assembly components are installed from the bottom up, with metal deck panels rolled out first and then mechanically fastened to the supporting structural joists or beams per manufacturer specifications using welds, screws, or power-actuated fasteners. Understanding the layered build up facilitates quality installation.
How to Install Metal Roof Decking
The roof deck provides critical structural bracing and support to the roof system, so proper installation is extremely important for performance and safety. Here are the key steps to install metal roof decking:
Safety regulations must be followed when installing metal decking at height. OSHA requires 100% fall protection for workers, which typically involves a personal fall arrest system.
Netting under decking is also an option. Safety railing around completed sections provides perimeter protection.
Standards for Finishes and Coatings
Most metal roof decking comes with protective factory coatings and primer finishes to guard against moisture during construction before enclosed as well as providing lasting corrosion resistance over the lifespan:
There are also hanger attachment products available with matching colors to roof deck primer. Consult your deck supplier for warranty specifics on coating performance – common standards range from 10 year paint warranties to 25 year galvanized guarantees.
Quality Assurance Through Testing
Reputable steel deck brands provide extensive testing documentation to support load tables and product claims. Testing per ASTM, SDI, ICC-ES, UL, Factory Mutual, and other administrations validates strength and construction suitability. Some examples include:
- ASTM A792 – Standard for Steel Sheet, 55% Aluminum-Zinc Allow-Coated by the Hot-Dip Process
- ASTM E1592 – Standard Test Method for Structural Performance of Sheet Metal Roof and Siding Systems by Uniform Static Air Pressure Difference
- SDI Publication No.30 – Design Manual for Composite Decks and Roof Decks
- UL 580 – Tests for Uplift Resistance of Roof Assemblies
This third party verification offers assurance to architects, engineers, and inspectors that the products will perform as specified. Here is a conclusion and FAQ section with answers to the 5 questions you requested for the article:
Conclusion
Metal roof decking is an integral component of commercial roof assemblies and multi-story structures. This corrugated sheet steel deck provides a durable, lightweight platform for anchoring roof membranes and transferring loads through to bar joists, beams, and columns below.
Understanding critical decking specifications like gauge, coating standards, profiling, strength capacities, and assembly details allows engineers and contractors to select and install high performing systems that safely withstand demand loads over occupied spaces.
By following manufacturer testing and recommendations as well as FM Global, IBC, OSHA protocols, metal roof deck protects facilities while enabling architects’ visions.
FAQ’s
What is roof metal deck?
Roof metal deck refers to structural, cold-formed steel panels installed above load-bearing walls, columns, and bar joists or steel beams to create the substrate that roof assemblies for commercial buildings are constructed upon.
What is decking on a roof?
Decking on a commercial low slope roof normally consists of corrugated metal panels known as roof deck. The steel deck provides the flat surface to attach roof insulation, membranes, and pavers over while transferring loads to the steel and concrete framing.
What kind of decking do you use for a metal roof?
For standing seam and other sloped metal roof products installed on purlins, typically 7/16” thick oriented strand board (OSB) or 3⁄4” plywood decking is used as the structural base. For low-slope commercial roofs, the decking is metal panels like 11⁄2” deep Type B roof deck or 3” Type N deck.
What is the process of metal decking?
The process includes first installing metal roof deck panels over steel bar joists, fastening with welds or screws at side laps and ends per code. Next insulation is set into asphalt over the deck and roof membrane applied. Perimeter flashings, gutters, and accessories complete the assembly.
How thick is metal roof decking?
Metal roof deck gauge (thickness) can range from 26 gauge, which is 0.551 mm (0.0179 inches) up to 18 gauge at 1.27 mm (0.0495 inches). Common specifications are 22, 20, or 18 ga. deck. Thicker material is stronger but higher cost. Standard galvanized G90 and Galvalume AZ55 coatings add additional thickness.