How long does a wood deck last?

A wood deck can last 20 years or more, and the range is wide for good reasons. Fairfax County's building official says that if the deck was built and inspected to code and maintained properly, it should last 20 years or more.^[1] The official adds that the answer turns on the materials used to build the deck, the quality of the work done by the builder, how the deck has been used and how often, and how well it was maintained.^[1] A deck built well, kept dry and refinished on schedule can go decades; a neglected one wears out much sooner.

Typical lifespans by part

A deck is not one thing that ages at one rate. The boards on top take the sun and foot traffic, the frame underneath stays shaded but can stay damp, and the metal ties it all together. Simpson Strong-Tie, which makes deck connectors, says most experts agree the average life expectancy of a wood deck is 10 to 15 years.^[2] The USDA Forest Products Laboratory is more hopeful: wood decks can, with minimal maintenance, provide decades of use.^[3] The gap between those figures is mostly care.

Why treated lumber matters

Rot needs moisture, and a deck lives outdoors. The Forest Products Laboratory says that without proper maintenance, wood decks develop checks, cracks, raised grain and mildew, increasing the risk of decay and insect attack.^[3] That is why, as the laboratory notes, lumber used in decks is usually pressure treated with a preservative, or is a naturally durable wood such as redwood or western redcedar.^[3] The difference is large. In Forest Service field tests in Mississippi, untreated southern pine sapwood stakes set in the ground lasted 1.8 to 3.6 years on average.^[4]

Treated lumber is graded by where it can be used. Under the industry's use categories, UC3 is for exterior wood used above ground, and UC4 is for wood used in ground contact.^[4] Fairfax's deck details warn that "Not all treated lumber is rated for ground contact,"^[5] and require that the cut ends of posts be field treated with a wood preservative containing copper naphthenate.^[5] A deck built with above-ground lumber where ground-contact lumber belonged, or with untreated cut ends at the posts, is more likely to rot early.

Finishing: the biggest factor you control

The Forest Products Laboratory is blunt: "Most decks are retired because of cracks and checks that mostly could have been avoided by timely finishing."^[3] Decks are exposed to severe weather that shrinks and swells the wood,^[3] the surface checks, and water gets in.

The kind of finish matters. The laboratory says penetrating finishes, not film-forming finishes, should be used on wood decks.^[3] The service life of a WRP finish is about 1 year on the exposed surfaces of wood decks,^[3] while the pigment in a semitransparent stain protects the wood surface from sunlight and increases the finish's service life.^[3] Paint is a poor choice for the walking surface: "Film-forming finishes, such as paints and solid-color stains, are prone to trap moisture and fail by peeling."^[3] Keeping a finish on the deck before it wears through does more for its life than anything else an owner does.

Other habits that add years

• Water is the enemy. Leaves and dirt packed between boards and at the house wall hold moisture against the wood, and a deck that cannot dry out rots sooner.
• Watch the metal. Metal connectors, nails and screws can corrode over time.^[2] Rust streaks on hangers, bolts or brackets are worth a professional look.
• Manage the load. Fairfax's building official suggests that you shovel the snow off your deck after a heavy snow fall to minimize the burden and wear,^[1] and not to add large, heavy items such as swimming pools or hot tubs on top of your deck.^[1]
• Inspect every year. The same official advises that you evaluate your deck annually and maintain it as recommended by your builder, and have it inspected regularly by a licensed contractor.^[1] The older your deck, the more often you should have it inspected.^[1] For composite, the county checklist asks: if your deck is composite is there mold growth, breakage or delamination?^[1] For what to look for at the house wall, see how to know if a deck ledger board is failing.

Older decks and arsenic-treated wood

Many Virginia decks are older than they look. EPA says that prior to 2004, wood treated with chromated arsenicals was used in residential structures such as decks and playsets.^[6] For such a deck, EPA says applying a penetrating protective coating such as oil- or water-based stains on a regular basis may reduce the leaching of chemicals,^[6] and it warns never to burn CCA or other preservative-treated wood in a residential setting.^[6] When an old deck comes down, the demolition crew should haul the treated wood away rather than burn it.

Composite decking

Composite and PVC boards are sold as low-maintenance alternatives to wood, and their makers back them with long written warranties. Trex, for example, warrants its decking lines for 25 to 50 years on a home, when properly installed, used and maintained.^[7] But the frame under most composite decks is still treated wood, with the same ledger, hangers and footings, so the structure ages like any other deck's.

When to call a licensed pro

Call one when the inspection turns up rot in the posts, beams, joists or ledger, corroded hangers or bolts, a soft or bouncy feel, or a deck pulling away from the house. Repairing or replacing those parts is structural work, and Virginia's building code says a permit is needed for installations or alterations involving any structural component.^[8] Virginia's Board for Contractors says work valued at $1,000 or more needs a valid Virginia contractor's licence,^[9] so check the contractor's licence before you hire. If it is time for a new deck, read what building a deck involves and what a deck costs in Virginia.

Find help on Loclis

Loclis lists licensed businesses from Virginia's DPOR register, with each one's licence number and class. Browse deck and porch repair or deck building, find exterior contractors in Blacksburg, see more exterior answers, or describe your deck once and local contractors quote the inspection or repair.