Deck Joist Repair: A Guide for Carolina Homeowners

A deck joist is one of the boards that run under the deck surface and carry it. On a typical deck the joists run from a ledger board fastened to the house out to a beam, and the beam rests on posts and footings. The deck boards sit on top of the joists, and metal hangers often tie the joist ends to the ledger.

Because the joists, beam and ledger sit under the deck boards, decay can progress out of sight. Homeowners usually notice the effects first, such as a soft spot underfoot or a section that dips.

Deck framing has no roof or crawl space over it, so it takes rain directly and then dries slowly in humid weather. Wood that stays wet between storms can decay. In the Piedmont around Charlotte, Greensboro and the Triangle, long humid summers slow that drying, and pines and hardwoods drop needles and leaves that pack between the boards and hold water on the joists.

Along the coast around Wilmington and Brunswick County, salt air and damp sandy soil keep the lower framing wet and can corrode the metal hangers and fasteners. Around Asheville, sloped lots can send runoff toward the posts. The rotted deck joist guide covers these causes in more detail.

Common signs include a spot that feels soft or springy underfoot, a section of the deck that sags or slopes, railings or posts that wobble, rust streaks or badly corroded hangers, and wood under the deck that looks dark or grayed and feels spongy. A gap opening between the deck and the house can point to rot at the ledger.

Sound wood resists a screwdriver tip. Wood that can be pushed into, flaked apart or pulled out in pieces has lost strength, and how wood rot is repaired depends on how far it has spread.

Deck joist repairs follow the same ideas as framing repairs inside a home. A joist that is weakened but still sound can be reinforced by sistering new lumber alongside it. A joist that has rotted through, especially at the end or the ledger, is usually replaced and reconnected. Corroded hangers and fasteners are renewed so the joists are tied in properly again, much like replacing failed joist hangers under a house.

The ledger connection deserves the closest look, because it carries the inner edge of the whole deck. How much can be repaired depends on how far the decay has spread and whether the ledger and beam are still sound.

Floor joists in a crawl space are protected from rain, but they can still soften when the crawl space stays damp. The repairs are similar: sistering weakened floor joists, replacing joists that have rotted through, and fixing the moisture that caused the damage.

HydroHelp911's framing repairs are under the house. If a soft deck has you wondering about the floor inside, our floor joist repair guide and sagging floor guide explain how we inspect and repair the framing beneath your rooms.