Even a 12-ft. by 14-ft. deck’s ledger has to support a minimum of two tons—a lot to ask of a single board screwed to the side of a house. In addition to gravity loads, we also have to make sure the deck can resist lateral load, which is the horizontal force that pulls a deck away from the house. For many years, the international residential code (irc) only gave us a performance criteria to meet: “Where supported by an exterior wall, decks shall be positively anchored to the primary structure and designed for both vertical and lateral loads.” Unless you hired an engineer to design the ledger and lateral-load attachments or you knew how to apply engineering principles, you couldn’t competently design and mount a code-complaint deck to a house.
Most of us now rely on prescriptive tables and illustrations to achieve a structurally sound, code-compliant ledger attachment. There are three main resources: prescriptive measures outlined in the irc, instructions provided by fastener or engineered- lumber manufacturers with an international code council Evaluation Service report (icc-ESr), or an “approved” technical guide provided by an industry association.
There are variations in deck sizes and loading, house framing, and deck-designer and deck-builder preferences. We can’t address every scenario in a short article, but here are the most common ledger and lateral-tie requirements for building decks on most homes. Some code jurisdictions have developed their own prescriptive deck-ledger attachment requirements and may prohibit some of the solutions presented here. Check with your local building-code official to ensure you’re following the locally enforced code provisions. also, remember that properly flashing a ledger is key to a safe, long lasting deck. For clarity, the drawings in this article don’t show WRB or flashing details. See my step-by-step videos in the Ultimate Deck Build for some of these.
Ledger Basics
The specified location of the lag screws or through-bolts ensures there’s enough ledger wood above the top row of fasteners and enough rim-joist wood below the bottom row of fasteners to reduce splitting. In addition, there are minimum and maximum distances the two rows of fasteners can be spaced apart. Proper pilot and clearance holes are also required, and the fasteners must be hot-dipped galvanized or stainless steel. Recessed heads are not allowed, nor are carriage bolts.
You cannot use the IRC’s prescriptive fastening schedule to build decks with live loads in excess of 40 psf or dead loads (decking, railings, and framing) more than 10 psf. Ground snow loads cannot be more than 40 psf. The connections must allow for inspection to ensure edge spacing and proper penetration (threads beyond nut for bolts and beyond tapered tip for lags).
Deck builders in snowy regions often build decks 5 in. to 7 in. lower than the interior floor level to keep snow from building up against doors that access the deck. This can’t be accomplished when following the IRC table, because of the required edge distances.
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