How much does it cost to repair water damage under a deck in NB?

Repairing water damage under a deck in New Brunswick typically costs $500–$5,000+, depending on how far the rot has spread and which structural components are affected.

Water damage repair is one of the most common deck jobs in NB — our combination of heavy snowmelt, 100+ freeze-thaw cycles per year, and persistent Maritime humidity creates ideal conditions for rot to develop, especially in hidden areas like the ledger board, rim joist, and post bases.

What Drives the Cost

Minor surface repairs — replacing a few rotted decking boards, sistering a damaged joist, or swapping out a post — typically run $500–$2,000. This assumes the damage is isolated and the structural framing is still sound. A contractor can often complete this in a day or two.

Structural repairs are a different story. If rot has reached the ledger board (the board bolted to your house), the rim joist of the house itself, or multiple posts and beams, costs jump to $2,000–$5,000 or more. Ledger damage is particularly serious — it can involve opening up your house's exterior wall, replacing sheathing, and installing proper flashing that should have been there from the start. In severe cases, a full deck rebuild is actually more cost-effective than patching a compromised structure.

The Most Common Culprit in NB

The single biggest cause of under-deck water damage here is a missing or failed ledger flashing. When the ledger board is attached to the house without proper metal flashing, water channels directly behind it, sits against the house framing through every freeze-thaw cycle, and quietly rots both the deck and your home's structure — often for years before anyone notices. If your deck was built without flashing (common in older NB builds), this is the first thing to address.

Post bases are the second major trouble spot. Posts buried in concrete or sitting directly on footings without proper standoffs trap moisture at ground level and rot from the bottom up. Replacing a rotted post runs $300–$800 per post depending on height and accessibility.

NB-Specific Timing

Have repairs done May through September when the wood is dry enough to assess properly and new pressure-treated lumber can be installed and sealed before winter. Avoid doing structural repairs in fall — you want at least one dry season for new PT lumber to acclimate before it faces its first NB winter.

Practical Steps Before Calling a Contractor

Probe suspicious areas with a screwdriver — sound wood resists, rotted wood gives way easily. Check the ledger board connection at the house, the top of every post, and any area where water visibly pools. Take photos of everything you find. This helps a contractor give you an accurate estimate without surprises mid-job.

This is firmly professional territory. Structural repairs — especially anything involving the ledger, posts, beams, or house framing — require a permit in most NB municipalities and need to be done by someone who understands load paths and NB Building Code requirements. A bad repair here is a safety hazard, not just a cosmetic issue.

New Brunswick Decks can match you with a local deck builder who can assess the damage and give you a free estimate — reach out and we'll connect you with someone in your area.