Practical Engineering: Holding It Together

Typical porch deck construction is joists running perpendicular to the side of the house. The joists are then supported by a ledger strip nailed to the side of the house. Is this strong enough? Let’s see. Suppose our deck is 6 feet deep by 12 feet wide, with joists placed 16 inches on-center. The inside ends of the joists sit on the ledger or in joist hangers attached to the ledger. A box joist is nailed into the outboard ends, and this box joist is supported by posts. Building codes specify a working design load of 60 pounds per square foot on small exterior residential balconies. Because the joists are placed 16 inches (1.33 feet) on-center, the load