How long does a deck last?

Lifespan by material

Those figures assume the deck is cleaned and, where relevant, refinished on schedule, and that the frame beneath stays dry. Neglect takes a third off the bottom of every range.

The frame is the real ceiling

Every deck in the table above is framed in pressure-treated lumber, whatever the surface is. That means a composite deck does not last 30 years because the boards do — it lasts as long as the joists, beam, posts and ledger beneath them.

Those members fail in a predictable order. The ledger goes first where water gets behind unflashed boards. Post bases go next where end grain sits on concrete or in soil. Joist tops rot where debris packed into narrow board gaps kept them wet. Fasteners and hangers corrode where the wrong metal was used against modern preservative treatments.

None of that is visible from above, which is why a deck can look fine the year before it needs rebuilding.

What shortens a deck's life most

1. No flashing at the ledger. This one item accounts for a large share of early structural failures.
2. Posts in ground contact. Wood sitting in soil or on wet concrete wicks moisture into the end grain and never dries.
3. Board gaps too tight. Debris packs in, holds water against the board edges and the joist tops, and rot starts in the one place nobody looks.
4. Wrong fasteners. Plain zinc-plated screws corrode in ACQ, CA and MCA treated lumber, sometimes within two seasons.
5. Letting the finish go. Once UV has broken down the surface fibres, a fresh coat no longer bonds properly and the wood erodes rather than weathers.
6. Enclosing the underside without ventilation. A skirted deck with no airflow dries more slowly than an open one and rots faster.

How to tell how much life yours has left

Take a screwdriver and spend twenty minutes on it. Push the tip firmly into the posts at ground level, into the ledger where it meets the house, into the joist ends, and into a few board ends. Sound wood resists; wood that takes the tip easily is already gone internally.

Then look at three things. The hangers and fasteners — rust streaks running down mean the metal is being attacked. The ledger — no visible flashing means assume water has been getting behind it for years. And the deck's behaviour underfoot: bounce that was not there before means a joist or a connection has moved.

A deck with a sound frame and tired boards is a resurfacing job at roughly half the price of a rebuild. A deck with a suspect ledger or soft posts is a rebuild whatever the boards look like — the repair or replace guide works through which one you have.

Getting the most out of it

• Clean once a year, in spring, before the finish goes on and before the season starts.
• Match the refinishing interval to the product, not the calendar: clear repellents annually, semi-transparent stain every two to three years, solid every three to five.
• Sweep the gaps out. Two minutes with a putty knife along the board joints each autumn does more for the frame than anything else on this list.
• Keep planters and mats off the boards, or on feet. Anything that holds moisture against the surface leaves a permanent mark and a soft spot.
• Check the flashing and the post bases every few years, not just the surface.