A free guide from the American Wood Council offers a great quick-reference and easy-to-read explanation of the 2012 International Residential Code (IRC), with a special focus on single-level wood deck construction in residential homes.
The American Wood Council document, called “The Prescriptive Residential Wood Deck Construction Guide” (available for download at this link) is an enormously helpful way to sort through the 2012 IRC, which is the operative code today.
The Guide, which is 44 pages, is worth reading in its entirety, because it explains and illustrates the code, but here below are seven key areas that every deck builder should be aware of.
1. Post size and connection
Figure 1: Use an approved post cap to attach beams to posts, and be sure to use the cap’s complete recommended nailing schedule. (Source AWC.org)
Don’t buy 4x4s for posts because they don’t meet code. The minimum post size is 6-in. x 6-in. nominal.
Where posts meet beams, the beams cannot be “sistered” along-side the post. The post must be notched (and the newly exposed wood treated with preservative), with the beam attached with at least 2 ½ in. diameter through-bolts with washers.
The beam has to fully bear on the notch.
Is there an alternative to notching? Yes, but you must use an approved post cap, like that shown in Fig 1.
See a selection of code-compliant “caps and bases” products from USP Structural Connectors, visit this link.
Figure 2. When assembling beams that are made up of three 2x members, note the nailing schedule required, as shown. If the beam is made up of spliced lengths, the splices must be located over interior posts. (Source AWC.org)
When constructing beams out of 2X material onsite, and the beam is made up of three members, then each outside member must be attached to the inside member with the fastener schedule shown in Fig. 2.
Be careful if you are splicing 2X material to make-up the beam. Each splice must occur over an interior post.
3. Joist Hangers
Figure 3. Note the joist hanger minimum vertical capacity (measured in Lbs.) joists ranging from 2x6 to 2x12.
All joist hangers must have a depth of 60% of the ledger or beam depth.
If you have a 12-in. beam, the joist hanger must be at least 7.2 inches. Specifically, 7.2 inches is approximately 7 ¼ inches, minimum.
The joist hanger minimum vertical capacity (measured in Lbs.) is shown in Figure 3.
4. Attaching Rim Joists
Figure 4. This drawing shows the required nailing schedule for fastening rim joists to joists, and deck board to rim joists.
Rim joists have their own requirements for how they are attached to deck joists. Drive fasteners through the rim joist into the ends of the joists with three 10d thread screws, or three #10 3-inch approved wood screws, see Figure 4.
Deck boards must be attached to rim joists in a prescribed method as well; also seen in Figure 4. Deck boards must be secured to the top of the rim joist with 10d thread screws, or #10 3-inch approved wood screws, 6 inches on center.
See the full line of USP fasteners at this link.
5. Prohibited Ledger Board Attachments
Figures 5 & 6: Do not attach ledger boards to exterior veneers or to cantilevered floor overhangs or bay windows.
Attaching the ledger board to the adjacent structure is a crucial connection because when it is done properly, the attachment prevents the deck from pulling away from the structure, which could lead to a dangerous, catastrophic failure.
There are numerous recommended ledger board attachment methods recommended in the Guide, but there three others worth highlighting, and those are the ledger board attachments that are prohibited:
- Attachments of the ledger board to exterior veneers of brick, masonry, and stone
- Attachments to hollow masonry
- Attachments to cantilevered floor overhangs or bay windows
6. Nails and Screws
All screws, bolts, washers, nuts, and nails used with treated wood must be either hot-dipped, zinc-coated galvanized steel, stainless steel, silicon bronze, or copper.
- Nails: ASTM F1667
- Wood screws: ANSI/ASME B18.6.1
- Bolts and lag screws: ANSI/ASME B18.2.1
You don’t need to know the spec specifically but look for manufacturers that advertise compliance with these ANSI and ASME regulations.
See USP Structural Connectors’ screws and nails at this link.
Flashing can be either “corrosion-resistant metal of a minimum nominal thickness of 0.019-inch thickness,” or approved non-metallic material.
Because of galvanic action, aluminum should not be used in direct contact with lumber treated with preservatives that contain copper (ACQ, Copper Azole, ACZA, or micro copper treatments).
Short of reading the entire 2012 International Residential Code (IRC), the American Wood Council’s Guide is a great shortcut for understanding the code as it applies to a deck. Even better, it’s a free download (link).