Attaching a Composite Deck Near a Floor Truss System
Technical note: Installation details vary by municipality, product line, board profile, fastening system, loads, and site conditions. Use this article as general guidance only; confirm the final design with your local building department, the manufacturer's current installation guide, and a qualified contractor or engineer when structural loads are involved.
Floor trusses differ from traditional framing. As with a roof truss, standard wood pieces (2x3 or 2x4) are assembled using metal connectors to create long, tall joists capable of accommodating HVAC ducts, plumbing, and other services between the trusses.
Understanding the Floor Truss System
Unlike conventional joists, floor trusses may not provide a conventional rim joist or ledger attachment point. Do not fasten a deck ledger to a floor truss system by guesswork; the connection must be detailed by an engineer, the truss designer, or the approved municipal plan.
- Axle without rim joist: absence of a rim joist around the floor, where ledger boards would normally be attached.
- Metal assembly: metal connectors linked to 2x3 or 2x4 wood sections.
- Increased height: long joists, 1.5 to 2 times taller than a classic 2x10.
Engineering Study and Attachment Methods
To ensure the solidity of your deck in Quebec, the first option is to have the system evaluated by an engineer who will define a connection method for a ledger board. The other solution is to design a freestanding deck, without direct connection to the load-bearing floor.
- Connection via ledger: possible only when an engineer or truss designer specifies the structural blocking, fasteners, and load path.
- Freestanding deck: independent structure, ideal for avoiding any stress on the trusses.
“This is not a connection to be taken lightly; various considerations are necessary.” - SBCA
SBCA Recommendations for Your Outdoor Living Space
The Structural Building Components Association (SBCA) publishes a detailed guide titled “Attachment of Residential Deck Ledger to Metal Plate Connected Wood Truss Floor System”. This document proposes five connection details for various scenarios.
- Wood blocking: ledger connection to a wood block added between the trusses.
- Specified blocking: use only structural blocking approved by the designer; composite deck boards are not structural ledger blocking.
- Truss ends: direct attachment to truss ends, depending on parallel or perpendicular orientation.
- Truss banding: horizontal element similar to a rim joist that connects the trusses and supports the ledger.
“Attachment of Residential Deck Ledger to Metal Plate Connected Wood Truss Floor System” - SBCA
Ensure the Durability of Your Outdoor Living Space
To guarantee the solidity of your Fiberon, TimberTech, Trex, or TruNorth composite deck, call on our experts in outdoor landscaping in Quebec. Benefit from a personalized study for a durable and reliable project.