Michael Polizzi, Sales Manager, A.C.T. Metal Deck Supply
Replacing metal deck for a commercial roofing contractor can easily range from often to never. Regardless of frequency, most would agree that an open roof is not the best time for a crash course on a metal deck! Hopefully, this article will provide you some tools you before you need them.
Originally from new construction, we got into the commercial reroofing market in the ‘90s and learned very quickly that this is a “now” business. My new favorite line I learned from a customer is, “I need it today, I’m planning ahead.” Before that it was, “What do you mean when? Aren’t my guys there yet?!”
Metal deck is provided with the steel package (division 5) in new construction, so it is only in reroofing when contractors may have to replace existing decking before installing a new roof. The “now” response is usually due to one of two things: (1) The deck was thought to be fine, turned out to be rusted through all but the paint or (2) A sudden visit by Mother Nature removed select parts of the building. Either way, the new roof is at a standstill until the deck is replaced.
What is Metal Deck Exactly?
Metal deck is a structural product. Structural is emphasized because it is not an architectural or finished, exterior panel. It is corrugated sheet metal engineered as part of the structural design of the building. A roof deck will have a roof system above it and can also be a form deck used for pouring concrete directly over it. There are many different steel panels, so a helpful way to know what metal deck is, is by knowing what it is not. In general, metal deck is not:
■ An architectural/metal building panel
■ Intended to be exposed on the outside of a building
■ Produced with a finished paint and warranty.
■ Produced in galvalume.
Four key factors for quoting or ordering metal deck efficiently are knowing the type, gauge, finish and quantity required.
Type
The most common types of roof deck are:
■ 1-1/2” B (wide rib)
■ 1-1/2” F (intermediate rib)
■ 1-1/2” A (narrow rib)
■ 3” N (deep rib).
The primary types specified in new construction are 1½” B deck and for longer spans, 3” N deck. The F and A profiles were common in the past and are now mostly used for replacement when matching existing panels. Roofing contractors are almost always matching and nesting into existing panels during replacement unless the project is a complete deck replacement. For this reason, it is critical to know the exact dimensions of the existing panels. These dimensions include:
■ The depth of the deck
■ The rib-to-rib dimension
■ The opening at both the top and bottom of the flute.
There are many obsolete profiles that have no exact match. A standard metal deck tip is knowing that F deck will nest into B deck and A deck will nest into both F and B deck. This will still not cover all situations because some of these extinct products have flute openings even tighter than the current A deck dimensions. A best practice is to take a photo of the existing deck with a tape measure on it and compare it to the dimensions of products currently in production. Confirming these dimensions prior to having material delivered to your roof will prevent delays and wasted labor hours.
Concrete Roof Systems
Lightweight concrete roof systems are installed on what are also known as form decks because they are the same products used to form floors. These decks are typically lower profile and lighter gauge panels installed over steel with closer spans. Form decks for lightweight concrete roofs include:
■ 9/16”
Knowing the rib-to-rib dimension should be especially heeded when trying to match 1” form deck. There are many profiles both current and obsolete with dimensions that vary slightly between ribs. Anyone who has ever dealt with matching these knows how quickly these panels fall out of sync when even slightly off.
Gauge
Roof deck ranges between 22 to 16 gauge with 22 being the most common. Lightweight concrete form deck ranges between 28 to 20 gauge. The lower the number, the thicker the steel. When the type or gauge of the deck is not clear, it is very helpful to know the joist or steel spacing. In this case, product load tables can be provided to an engineer for specification.
Finish
Metal deck is a structural product and most commonly comes galvanized or prime painted. Finishes include:
■ Prime painted gray
■ Prime painted gray on top with a primer white bottom
■ Galvanized in a G60 or G90
■ .60 oz./per sq. ft. vs. .90 oz./sq. ft. of zinc
■ Galvanized plus a factory applied primer
■ Stainless Steel – for food-grade or extremely corrosive environments.
For prime painted deck, the Steel Deck Institute (SDI) Design Manual states, “Prime paints by nature are impermanent and provisional. Prime paint alone will only protect the steel for a short period of time under ordinary exterior atmospheric conditions.” Remember, this is not a finished paint.
For galvanized deck, the language has grown more extensive in recent years but earlier SDI manuals stated, “In corrosive or high moisture environments, a galvanized finish is desirable.” A chalky film or “white rust” forms when galvanized deck is exposed too long to moisture. It is a chemical reaction from the zinc’s “self-sacrificial characteristics” protecting the steel. The steel is structurally sound but in cases without a drop ceiling, it may not be a preferred aesthetic by an owner.
Of course, you want the best possible product for your customers, so it is worth learning the proper handling of these finishes in order to protect your work. Properly handled, metal deck will look great and last a very long time but if left exposed to the elements too long, it can rust or develop rust staining. The SDI Design Manual regarding site storage instructs, “steel deck shall be stored off of the ground with one end elevated to provide drainage and shall be protected from the elements with a waterproof covering, ventilated to avoid condensation.” Ventilating the bundle is especially important so that moisture does not get trapped.
Quantity
Asking for the correct quantity may sound like common sense but how that quantity is communicated can mean all the difference for an accurate and timely quote. A common miscommunication can happen when a square foot price is put into a bid but when buying stock length sheets, the actual square footage purchased exceeds what you sold. Here are some helpful examples for your RFP:
■ Total square footage needed (supplier to qualify “final price based on final list”)
■ Dimensions of areas to be covered
■ Exact cut list desired
■ Square foot budget pricing.
Fastening: With What and Where Exactly?
Metal deck can be fastened with welds, screws or shot down with pins. Most commonly used for metal deck
replacement is the self-tapping screw, considering welding sparks and pins shot from a tool cause unnecessary
risks over an existing structure.
The fastening pattern is what tells the installer exactly where to fasten the deck both to the supporting steel and at the sidelaps between the span. Breaking down the common code “36/4 w/1” means:
■ 36 = The width in inches of one panel (panel widths vary)
■ /4 = Four fastening points “per” 36” panel on the steel support
■ w/1 = “With” one sidelap screw per span (number will vary).
There are many fastening patterns that are important to follow because they are part of the structural design of the building.
There are other metal deck products, accessories and finishes but most issues will be solved by remembering
above all that:
■ F fits into B and A fits into both F and B
■ Type, gauge, finish and quantity
■ Know your dimensions.
When the answer is so often, “I need it now!” hopefully this has you well prepared with the tools you’ll need…Before you need them.
FRM
Michael Polizzi is the Sales Manager for A.C.T. Metal Deck Supply. This FRSA Associate Member is a metal deck distributor with 15 locations in 11 states including locations in Jacksonville and Orlando. For more information, call 800-894-7741 or visit www.metaldecksupply.com to view the Metal Deck 101 video series
