This past week, we reviewed section 4, on joists, in this multi-part article on the structural components of decks and the main elements of the structural load path, both from a bearing and uplift resistance perspective.
Altogether we are discussing the following items, in this 6-part series, and today we will focus on ledger boards:
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- Footings
- Columns
- Girders
- Joists
- Ledgers
- Rim Joists
In a previous article, we discussed some of the details related to ledger board installation to connect a deck back to the main building. Today we’re going to take a deeper look at the ledger board as part of the main structural components of a deck, section number five in this six-part series.
A ledger board ties the deck to the exterior wall of a building or house, so it is a key structural component in deck construction, serving as the principal connection point between the deck and the main building. This horizontal board (or framing member which could be built similarly in steel deck construction) is fastened to the exterior wall of the house or other supporting structure, providing a solid connection point for the deck’s framing and joists.
The primary function of the ledger board is to transfer the loads and weight of the deck structure back to the main building. As people walk, furniture is placed, and other live and dead loads are applied to the deck surface, these forces are transferred through the deck boards, joists, and ultimately to the ledger board. The ledger board then distributes these loads into the home’s framing system, ensuring the deck remains stable and secure.
Proper installation of the ledger board is needed for the overall safety and longevity of the deck. It must be attached using lag screws or through-bolts at regular intervals, securely embedded into the home’s structural framing members, such as rim joists, exterior masonry structural walls, or interior framing. This connection not only transfers the vertical loads but also resists lateral forces caused by wind or seismic activity, preventing the deck from separating or pulling away from the building.
In addition to its structural role, the ledger board also serves as a reference point for establishing the correct height and level of the deck framing. Precise installation of the ledger board ensures that the joists and beams are properly aligned, resulting in a level and stable deck surface.
Mounting with structural stability and strength affects the safety of the entire deck system. Someone might think or assume that the deck just has to resist the deleterious effects of natural deterioration over time but that’s not the complete picture. The deck also has to be able to withstand the live loads of the occupants and were furniture, weather conditions including severe storm and high winds and even uplift factors that might happen from gale force winds. There are several important steps and methods commonly used for securely attaching the ledger board to the main building.
One of the most widely accepted techniques is to lag bolt the ledger board directly into the home’s structural framing members, such as the rim joist or wall studs. This involves first removing any siding or exterior finishes to expose the framing. The ledger board is then positioned flush against the wall, and holes are drilled through the board and into the framing at regular intervals, typically every 16 to 24 inches. Heavy-duty lag screws or through-bolts with washers are then driven through the ledger and securely anchored into the framing. We’ve looked at bolting patterns in past blog articles on our website and even included some diagrams showing diagonal staggered bolting patterns.
Another method, often used when rim joists or studs are not accessible, is to install the ledger on stand-off blocks or mounting plates. These spacers create a gap between the ledger and wall, allowing the lag bolts to pass fully through the framing. The blocks or plates are first anchored to the wall’s structural members, and then the ledger is lag bolted directly into these supports.
Regardless of the mounting method, proper flashing and waterproofing details are essential to prevent moisture intrusion behind the ledger board. This may involve installing self-adhering membranes, Z-flashing, or other weatherproofing materials between the ledger and wall surface to divert water away and protect the building envelope.
Additionally, securing the ledger board alone is often not sufficient. Lateral loads must, in many cases, also be resisted by anchoring the deck’s end joists or beams to the home using tension ties, angle brackets, or other approved connections to prevent the deck from kicking out or separating from the structure. The connection between the ledger board and the main building structure is critical not just for bearing the vertical loads, but also for resisting horizontal forces acting on the deck. A proper ledger connection must be designed to handle both compressive (bearing) and tensile (pulling) loads, as well as shear forces.
From a bearing perspective, the ledger board transfers the deck’s full weight, including live loads from people, furniture, and any other objects, down through the joists and onto the home’s framing. This compressive force must be adequately distributed along the length of the ledger to prevent localized crushing or failure of the framing members. Proper spacing and sizing of the lag bolts or through-bolts is essential to ensure sufficient bearing capacity.
However, the ledger connection is also subject to significant tensile forces, particularly from lateral wind loads or seismic activity. These horizontal forces can try to pull the deck away from the building, putting immense tension on the ledger fasteners. If the connection is not properly designed and installed to resist these tensile loads, the deck could potentially separate from the structure, leading to catastrophic failure.
Shear forces acting parallel to the ledger board are another crucial consideration. As the deck sways or shifts laterally, shear stresses are induced along the length of the ledger and its fasteners. Insufficient shear capacity in the connection can lead to the ledger board tearing away from the framing, compromising the entire deck’s structural integrity.
To address these tensile and shear demands, various reinforcement techniques may be used. These can include the use of specialized structural screws or bolts designed for high tensile and shear loads, the addition of sturdy metal tension ties or brackets, or the incorporation of engineered wood products like multi-ply ledger boards for increased shear strength.
By considering and accounting for the bearing, tensile, and shear forces acting on the ledger board connection, you can ensure a strong and safe deck structure that will withstand not only the vertical loads but also the substantial horizontal forces it may encounter over its lifespan.
The connection requires particular mechanical fastening to properly mount and support the deck, from a structural perspective. One of the most common methods involves the use of joist hangers, which are metal brackets designed to securely hold the joists in place. Joist hangers are typically nailed or screwed into the rim joist, providing a sturdy seat for the joists to rest in. The joists are then toenailed or clipped into the hangers, creating a solid connection that resists uplift and lateral forces. Proper hanger sizing and nailing patterns, as specified by the manufacturer, are needed to achieve the required load-bearing capacity.
In addition to joist hangers, other mechanical connections may be employed, such as structural screws or framing anchors. These specialized fasteners are designed to provide enhanced shear and withdrawal resistance, further strengthening the joist-to-rim joist connection.
For added lateral stability, the deck frame may also incorporate diagonal bracing or blocking between the joists. These additional framing members, when properly fastened, help distribute lateral loads and prevent excessive racking or twisting of the deck structure.
In some cases, particularly for larger or more complex deck designs, engineered wood products like multi-ply rim boards or specialized metal connectors may be used. These products offer increased strength and load-bearing capacity, ensuring the deck can withstand substantial vertical and lateral forces.
Regardless of the specific methods used, it is essential to follow local building codes and manufacturer’s instructions for proper installation and fastening of these mechanical connections. Ensuring a secure and robust rim joist-to-joist attachment is crucial for the overall structural integrity and longevity of the deck system.
Use a contractor who understands and cares about doing things right. Always, feel free to reach out to us here at Dupont Decks and Patios. You can call us at (202) 774-9128. You can find us online at https://dupontdeckspatiosdc.com and you can email us there as well at https://dupontdeckspatiosdc.com/contact-us
