Porch & Deck Ledger Connections to Buildings - Construction Details InspectAPedia® -
Deck & Porch Construction Materials Choices
Deck & Porch Construction & Structural Fasteners
Deck & Porch Construction Details for Safety
Deck & Porch Railings, Code Requirements, Safety
Finishes for Exterior Decks
Poor Construction Details and Improper Connections Can Lead to Dangerous Collapse of Decks and Porches
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Here we discuss critical safe-construction details for decks and porches, including avoiding deck or porch collapse and unsafe deck stairs and railings. This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.
Also see our review of that book. Also see DECK COLLAPSE Case Study (collapse of a new code-approved deck) and DECK FLASHING LEAKS, ROT Case Study for an example of an older deck with rot and collapse due to improper construction and missing building flashing.
Photos & Construction Details of Unsafe Compared with Safe Deck & Porch Connections to the Building
Deck Ledger Board Connection to Building Band Joist
Most residential decks are supported on one side by a ledger that is bolted or lagged to the home’s band joist. This connection is critical, since a failure here can cause a deck to collapse. Deck Collapse Case Study describes several improper connections between a residential deck and the building that led to the catastrophic deck collapse shown here.
Failure of the ledger can be caused by too few or undersized fasteners, or by decay in the ledger or band joist. Lags or bolts provide little support when fastened to rotted wood. So proper flashing of the ledger and band joist area is critical.
It is also important that the band joist be nailed adequately to the surrounding structure, since the ledger is only as strong as the structural members it is attached to.
Though deck failures are rare, ledger connections are typically at fault when they occur. Through-bolts make the strongest connection, but adequately sized lag screws can also work. With either, it is critical to flash the ledger area and to only use metal components that are compatible with pressure-treated wood.
Our photo (left) shows what can happen if the deck ledger board is simply nailed to the structure. Deck Collapse Case Study includes additional photos of improper connections between a residential deck and the building that led to a catastrophic deck collapse.
In new construction, if a deck is planned, make sure the band joist is pressure treated and adequately nailed to the sole plate above and the sill or top plate below, using stainless-steel or double-hot-dipped galvanized nails.
Fastening with 16d common nails at 8 inches on-center is recommended. If the nailing cannot be confirmed in a retrofit, extra toenails driven through the exterior can help to reinforce this connection
The table immediately below gives the bolt spacing requirements for connecting a deck ledger to the building when the ledger board is bolted directly to the structure.
Table of Bolt Spacing for Deck Ledger Spaced Away from the Building
Spacing for bolts and lags used to connect the deck ledger to the building are shown in the table at above-right (ledger bolted directly to the building), and at in the figure at left for deck ledgers that are spaced away from the building.
Through-bolts are the most reliable connection, but lag bolts are adequate (photo, above left) as long as they are long enough to fully penetrate the band joist. For through-bolts, drill holes 1/16 inch larger than the bolt. For lags, drill a full-diameter hole for the unthreaded portion and a smaller hole (65 to 75% of the lag’s diameter) for the threaded portion.
Use washers under the head of the lag bolt or at both ends of through-bolts to keep the head from crushing the wood. Soak the holes with a preservative before inserting the bolts.
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Wiley.com and also at Amazon.com. See our book review of this publication.
Manual for the Inspection of Residential Wood Decks and Balconies, by Cheryl Anderson, Frank Woeste (Forest Products Society), & Joseph Loferski, October 2003, ISBN-13: 978-1892529343, $39.00 at Amazon.com or at the InspectAPediaBookstore
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