What Is Double & Triple Span in Metal Decking?

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Metal deck surfaces mimic the appearance of wood.
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Metal decking is a long-lasting, low-maintenance alternative to wood decking. Metal decking is available in a modular system, where prefabricated aluminum panels fit together, or a plank system, where installers place smaller, individual pieces, one at a time, on site. Both types of systems attach to a metal frame structure for support.


Double- and Triple-Span

Installers attach planks and modular panels of aluminum decking to metal joists. Double-span decking uses surface material that is long enough to bridge the gap between two joists, hence the term "double." Triple-span decking uses surface material that spans three joists. Metal decking plans call for joists to be 24 inches apart, so a double-span deck plank is at least 48 inches long, and a triple-span deck plank is at least 72 inches long.


Metal decking manufacturers coat the surface of the deck material so that it resembles stained wood. They offer coatings in a variety of colors and textures, including faux "weathered" finish. The coating is also functional; it dampens sound and keeps the metal decking cool enough to walk on. Waterproof and nonskid finishes are also available -- practical choices for metal decking around a swimming pool.



Decks made of engineered materials, such as aluminum, are generally more stable than decks made of wood because of the variations of quality that occur in natural materials. Modern manufacturers use machining processes that result in precise cuts and warp-free products. The precision of the metal parts makes the interlocking modular systems possible. The systems use clips and screws to join modular units.


Metal decking needs little care compared with wood decking. The coating on a metal deck will not weather or fade. One manufacturer recommends that a homeowners clean their metal decks at least twice a year using water and a mild detergent to remove the dirt and stains that are bound to accumulate on any outdoor surface. A homeowner may need to use mineral spirits or turpentine to remove stubborn stains such as tree sap and paint.



Marilyn Lindblad

Marilyn Lindblad practices law on the west coast of the United States. She has been a freelance writer since 2007. Her work has appeared on various websites. Lindblad received her Juris Doctor from Lewis and Clark Law School.