Failure of the ledger board—the structural member placed to attach an outdoor deck to the primary structure—is the leading cause of deck collapses. Ledger boards can fail for a lot of reasons, including:
· Incorrect lumber type and size with respect to the load
· Fastening to a non-structural element or assembly
· Inappropriate fastener selection by type, size, material and/or finish
· Inadequate number and placement of fasteners
· Failure to provide adequate resistance to lateral forces
· Rot caused by inadequate flashing and/or drainage
Choose the right lumber type and size. Solid-sawn two-by, preservative-treated Southern pine or hem-fir is typical for ledger boards. A ledger should be a minimum of 6 inches wide and at least the same width as deck joists. Choose the straightest board available for a deck ledger.
Fasten a ledger to a structural component or assembly. There are several typical possibilities. Choose the method best suited to the design of the deck and the adjacent structure:
When ledger will be fastened to a solid sawn rim board running perpendicular to floor joists in the primary structure. Remove exterior siding if present and expose sheathing in the region of the rim board. Apply a waterproof membrane to the sheathing in the area where the ledger will be fastened, lapping the membrane underneath existing weather barrier (e.g., housewrap, asphalt felt, etc.) at least 6 inches.
Cut the ledger stock to length. Lay out positions of the deck joists. Bore holes for the fasteners that will be used to attach the ledger to the rim joist—two aligned not less than 2 inches from each end and for additional fasteners to be staggered along the board length not less than 2 inches from the top and bottom edges. Follow fastener spacing specs published in 2009 International Residential Code (IRC), Table R502.2.2.1.
As you plan the fastener layout, take care that bolt heads won’t occur where joists will be joined to the ledger. If you plan to use solid spacers behind the ledger (rather than stacked washers), lay out their positions on the back of the ledger, and plan to bolt through them.
Fasten the ledger through the sheathing to the rim joist with ½-inch (min.) through-bolts (preferred) or lag screws, leaving a ½-inch airspace behind the ledger to prevent moisture from becoming trapped. Lag screws, bolts, and washers should be hot-dipped galvanized or stainless steel. Install a formed sheet metal or PVC flashing over the top edge of the ledger.
While a ledger-rim joist connection made according to IRC specs should be adequate to resist shear (in this case, downward) forces, it may not provide enough resistance to lateral forces, which can pull the ledger and rim board away from the house. The best practice, suggested by IRC R502.2.2.3, is to use hold-down tension devices to tie deck joists to floor joists of the primary structure in at least two locations.
When the deck ledger will be fastened to a solid-sawn rim joist that runs parallel to floor joists in the primary structure. While the specs and procedure are largely the same as those for a ledger installed perpendicular to floor joists in the primary structure, when a ledger will be fastened to a rim joist, the floor frame should be reinforced. Install solid blocking of equal width to the floor joists between the rim and the joist next to it. Use tension brackets to fasten the side of the blocking to the face of the joists at each end. Some pros recommend sistering the rim joist to a 2-by of equal width and installing blocking between the second and thirds joists, as well, to further reinforce the floor frame. Use hold-down tension devices to tie the deck joists to the blocking between floor joists in at least two locations along the ledger-rim joist connection.
When the deck ledger will be fastened to a floor frame constructed with I-joists. If the rim joist to which the ledger will be attached is 1-1/4-inch LVL or 1- 1/8-inch LSL, follow the procedure for attaching the ledger prescribed for attaching to solid-sawn rim boards (above). [set anchor link] But if the rim board is an I-joist with a thin plywood or OSB web, seek an engineer’s advice and approval for another solution. If possible, consult the I-joist manufacturer for a recommended strategy.
JLC pros typically advise cutting blocking from 2-by solid lumber or LVL to fit between the I-joist flanges to reinforce the web. [http://forums.jlconline.com/forums/showthread.php?t=56956&highlight=deck+collapse] The blocking should be glued with construction adhesive and screwed in place. Note that the webs of I-joists running perpendicular to the rim board must be similarly reinforced where tension hold-down devices will be installed to manage lateral forces.
When the deck ledger attachment point is a stucco-finished wall. Cut the stucco back to the framing with a masonry saw. In the process, cut away and remove any underlying wire lath. Slip a piece of flashing (galvanized steel would be the best choice to be compatible with the steel wire lath) about 3 inches up under the building paper or other moisture retarder underlying the stucco.
When the deck ledger will be attached to a concrete wall.Most codes allow a ledger to be attached to a structural concrete wall with ½-inch (min.) expansion anchors embedded at least 2-1/2 inches into the concrete. Follow recommendations in the table “Ledger Fastener Spacing for Masonry Walls.” Two caveats here: 1. A noted engineer who has studied causes for deck collapses observes that while the recommended anchors are load rated, the structural strength of the concrete is seldom known to remodelers. [http://www.deckmagazine.com/article/62.html] 2. Expansion anchors in deck ledger applications may not adequately resist the lateral forces that are known to cause a great number of deck failures. If there’s any doubt on either issue, seek an engineer’s advice.
Some experts recommend supporting ledger boards fastened to concrete walls on posts anchored along their length to the wall and supported by footings. Also consider a freestanding deck design as a safer alternative to fastening ledger boards to masonry.
When a deck ledger will be attached to a hollow concrete block wall.Attach a ledger to hollow masonry block with adhesive anchors (e.g.,Epcon A7[http://www.ramfast.co.th/pdf/EpconA7FA2.pdf] or theHilti HIT HY 20 system) [http://www.us.hilti.com/holus/page/module/product/prca_rangedetail.jsf?&nodeId=-60853&selProdOid=434591]. The threaded rod used with the anchors must be at least 1/2- inch in diameter and must penetrate the block by at least 3-1/2 inches. Caulk the joint where the top of the ledger meets the block.
When the deck ledger attachment point is a brick veneer wall.Most professional engineers recommend against attempting to support a deck ledger on or through brick veneer. [http://www.jlconline.com/cgi-bin/jlconline.storefront/4ebbf59f0567112a27170a323cb40676/UserTemplate/69?s=4ebbf59f0567112a27170a323cb40676&c=b04bff44d23d0a4138c0e8067f269cc8] Instead build a freestanding deck that’s independent of the primary structure. [“Ledgers on Challenging Walls,” http://www.deckmagazine.com/article/62.html]
Go to: Decks: Structural Materials and Decking Selection