COMPONENTS
Critical components for long term performance of decks and balconies?
- Support columns: Support columns need to be designed for the maximum load expected and the unsupported height of the column. Notching of columns as is sometimes done at beam or girder connections, needs to be properly designed, detailed, and constructed to provide a safe support for decks.
- Ledger connections: Ledgers, the members attached to the exterior walls which the deck’s joists are connected to, are critical components to a deck's performance. Ledgers typically lag bolted to the exterior walls. The allowable loads for lag bolts are quite low and, for typical deck sizes, require multiple lag bolts for each joist. Deck joists are typically supported from ledger boards with metal joist hangers which have high allowable loads and are rarely a problem if they are installed according to the manufacturer's instructions. Ledgers also create other problems for the support of decks. Ledgers create openings within the exterior walls where water can penetrate to the interior of the walls causing deterioration of the wall components. Proper flashing and water management details are critical for the long-term performance of decks.
- Guardrails: Guardrails are required to safely support a 200-hundred-pound load, acting in any direction, at any point along the top of the guardrail or a 50 pound per foot load, acting in any direction, along the top of the guardrail. These loads must be safely transferred through the supports to the structure. The connection of the handrail posts is a critical component of guardrails. Guardrails are required by code to be 42 inches above the deck surface. This height combined with the required 200-pound load creates a large bending force at the base of handrail posts. Handrail posts bolted to the joists typically do not have the design strength to resist these loads without additional blocking or straps to secure the posts.
Decks and balconies are an attractive and well used feature in residential structures. However, they can be deadly if their design, construction, and maintenance are not carefully considered. By their very nature, they are exposed to the damaging effects of weather and typically interrupt the structure’s weather resistant cladding at their connections to the structure. Homeowners and condominiums boards should be aware of these potential dangers and institute inspection and maintenance programs for decks and balconies.
If you have questions concerning the structural integrity of your deck or handrails, it’s best to call a NADRA Professionals member( Deck Builder - NADRA) or structural engineer to provide a professional opinion.
Anatomy of a Deck, Railing
