Check Yourself Before You Deck Yourself

Originally published by the following source: SBC MagazineApril 29, 2019
by Evan Protexter, EIT

   

According to HGTV.com, adding a deck, patio, or porch to an existing home returns 90% of the money invested at the sale of the home. While an outdoor living space is something that homeowners desire, either for personal use or for potential resale value, the structural implications of adding a deck to a home constructed with floor trusses are significant. In order to prevent deck installation from becoming an issue, there are a few things components manufacturers (CMs) should be aware of if clients are interested in preemptively or retroactively installing a deck- ledger.

Why might it be an issue to connect a deck ledger to a wall where floor trusses are used? One reason is because the provisions for attaching a deck ledger called out in the IRC are prescriptive and pertain to attaching the ledger to 2” nominal band joist bearing directly on a sill plate or wall.

R507.2.2 Band joist details

Band joists attached by a ledger in accordance with Section R507.2 shall be a minimum 2-inch-nominal (51 mm), solid-sawn, spruce-pine-fir lumber or a minimum 1-inch by 91⁄2-inch (25 mm x 241 mm) dimensional, Douglas fir, laminated veneer lumber. Band joists attached by a ledger in accordance with Section R507.2 shall be fully supported by a wall or sill plate below.

What that means is that the prescriptive method assumes that nails will be driven into a continuous piece of wood, which is not the case when trusses are used. The second reason is that floor trusses are not typically designed and installed to resist lateral loads, only gravity. This means decks installed on the side of trusses, versus the end, require additional lateral reinforcement.

These are minor issues overall and floor trusses still allow a deck to be installed, but CMs must ensure that correct action is being taken during installation to support the load. Communicating the industry’s best practices on installing deck ledgers with floor trusses is the best way to prevent unnecessary structural issues from occurring.

For this purpose, SBCA has assembled a topical library with information to answer almost any question out there regarding floor trusses. An answer to this particular issue, along with a research report on the subject and installation guide can be found on the SBCA website.

For additional information on deck ledger truss attachments, please read the following articles:

  1. Deck Ledger Boards
  2. Guidance on Deck Ledger Attachments to Floor Trusses
  3. Attachment of Residential Deck Ledger to Metal Plate Connected Wood Truss Floor Systems - Educational Program

 

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