Importance of a Properly Installed Ledger
Deck ledgers are one of the most crucial structural members in deck construction. Their significance and method of attachment to the supporting structure is often overlooked. Because of this, more than half of structural failures in decks result from poor ledger to house connections. These failures are most often caused by improper fastening to the floor rim joists/structural framing, or rotting wood due to poor moisture management.
Code Applications
It is typical across all codes that the minimum ledger size is 2×8 and must either match or exceed deck joist dimensions. BCBC 9.3.2.9 states that exterior structural elements exposed to precipitation must be pressure treated to resist decay. Ledgers cannot rely on nails for fastening and must use either lag screws or preferably through bolts if possible to ensure a highly secure connection to the structure of the house. These fasteners are required to be hot dipped galvanized steel coated with zinc in accordance with ASTM A153/A153M, stated in BCBC 9.23.2.4. Furthermore, the structure being connected to must be fully supported and not a cantilevered floor system. Many decks require ledger connections to have additional tension ties installed for lateral support adhering to BCBC 9.17.2.2. Flashing installation requirements covered in BCBC 9.27.3.8 indicate that in most cases where there is a break in cladding, installation of flashing to divert water is required.
Best Practice
The Canadian and BC Building Codes do not provide more comprehensive guidance in detail, however BC Housing references the International Residential Code (IRC) for insight on fastener spacing and placement on the ledger. This code suggests that when using lag screws, maintain a maximum vertical spacing of 5″ in a staggered pattern, with a minimum edge distance of 2″ at the top, 3/4″ minimum at the bottom, and 2″ minimum at the ends. A 1/2″ stacked washer gap between the ledger and wall is permitted and is a recommended measure to include for open decks, as it allows for airflow and drainage of any moisture that gets behind the ledger. The IRC provides a fastener spacing table which varies with span of the deck joists, however each project must meet engineering specs in regards to screw or bolts patterns and spacing. The BC Housing guide “For Building Safe and Durable Wood Decks and Balconies” has illustrated a typical best practice deck connection for drip-through decks and membrane decks as seen below.
The ledger is a critical connection for deck construction, and it is essential to provide a proper strong connection to the house. By incorporating all necessary measures to keep moisture away and using the correct choice of fasteners, decks can remain safe and durable for their entire intended lifespan.
Have any questions? Reach out and we’d love to chat!
By Harrison Sweet, co-op student with our Lower Mainland office
Photo Credits:
https://www.caseydevoti.com/deck-safety-101/
https://www.bchousing.org/publications/IG-Building-Safe-Durable-Decks-Balconies.pdf