Attaching Decking to Metal Deck Framing

Metal Joist Framing Systems

A major new trend in the decking industry is the growing use of metal joist framing systems. While treated lumber will remain the most common substructure for residential decks in the near future, builders and homeowners now have the option of using steel and aluminum deck framing systems, which have several important benefits.

First, metal joist systems are now required in some areas to meet building codes, particularly in dry areas where wildfires are a concern as well as in some dense urban settings. Secondly, decks built with metal joists are more durable and have a more uniform and flat surface compared to decks built with treated lumber. For builders who use premium quality decking materials, it is only natural to want to have the best possible substructure.

In addition, while building codes and consumer demand have led to a growing interest in metal joist systems, this segment of the decking market has been held back considerably by a lack of deck fasteners suitable for attaching PVC, composite, capstock and hardwood decking materials to steel and aluminum. Standard deck screws, whether they are designed for hardwoods or particular plastic or composite decking materials, are simply not functional with steel and aluminum. While some builders have developed improvised or nonstandard methods for attaching decking to metal joists, these applications are typically more difficult and time consuming than most builders are accustomed to when building standard treated lumber decks.

Attaching Decking to Metal Deck Framing

To help address this need, the Deckfast Metal fastener from Starborn Industries was introduced specifically for attaching decking to metal joists. This new fastener is approved for use with both Trex Elevations steel deck framing and Wahoo Decks aluminum joist systems, and is available in colors to match popular decking products.  

In general, deck screws designed to attach decking materials to metal joists are basically hybrids of self-drilling sheet metal screws and composite deck screws. The self-drilling point is able to penetrate through metal. With the use of composite materials in particular, it is also very useful to have wings above the drill point, which clear the decking material away from the drill point so that it can cut through metal as quickly and cleanly as possible. (Once the wings hit the metal, they shear off). The head of the screw is typically a “cheese head” design, with an undercut below the head that is designed to penetrate cleanly through the hard outer surface of capstock and hardwood decking materials.

Finally, since one of the main concerns of deck builders and homeowners who choose to use metal joist systems is the longevity of the deck, it is important to consider the corrosion resistance of the deck fastener. With premium decking materials and the additional costs of using metal joists, it is only natural to want to have superior corrosion resistance. The types of stainless steel deck fasteners that builders typically use for decks near bodies of water or for use with particular decking materials, are not suitable for use with metal joists – grades 305 and 316 stainless steel are too soft to penetrate through steel and aluminum. For attaching decking to metal joists, a hardened version of stainless steel – grade 410 – is required. Additional corrosion resistance on top of the grade 410 stainless steel is also available with the use of epoxy coatings, which can also be color matched to specific decking products, so that the deck fastener is barely visible on the decking surface.

These critical advances in the design of deck fasteners are, ultimately, what will make metal joist framing systems for decks feasible for homeowners and builders who are interested in building the highest quality decks.

Concord Carpenter

Who is Concord Carpenter?    ~ Robert Robillard is editor of A Concord Carpenter and principal of a carpentry and renovation business located in Concord, Massachusetts. Rob is a recognized leader in tool and how-to information for building professionals, he also hosts the Concord Carpenter Cable TV Show, offering the do-it-yourself audience in Boston's Meto West region expert advice on home repairs and maintenance. On his website, Rob covers all aspects of home improvement and remodeling, specializing in problem solving for home maintenance. Rob enjoys evaluating and reviewing tools and products and restoring vintage tools. The Concord Carpenter's motto: "Well done is better than well said!":

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