Deck Addition Cost Guide 2026

Deck additions are one of the few home improvement projects that homeowners consistently enjoy while they own the home and recoup a meaningful chunk of at resale. The challenge is that cost estimates vary wildly because deck projects range from a simple ground-level platform to a multi-level structure with built-in seating, pergola, and outdoor kitchen rough-in.

A 300 to 400 sq ft deck in pressure-treated lumber runs $15,000 to $22,000 installed nationally. The same size in composite decking runs $22,000 to $35,000. Those numbers go up significantly for second-story decks, irregular shapes, or any structural complexity.

Wood vs. composite

Material	Installed cost (400 sq ft)	Lifespan	Annual maintenance
Pressure-treated lumber	$15,000 – $22,000	15–25 years	Sand + stain every 2–3 years
Cedar or redwood	$20,000 – $30,000	20–30 years	Stain every 2–4 years
Composite (Trex, TimberTech)	$22,000 – $35,000	25–30 years	Wash annually, minimal upkeep
PVC decking	$25,000 – $40,000	30+ years	Wash only, no staining

The framing and structural elements are almost always pressure-treated lumber regardless of what you choose for the decking surface. The cost difference between wood and composite is primarily in the decking boards themselves and the labor to install them.

Composite pays back over time. The higher upfront cost often pencils out over 10 years when you factor in the staining and sealing you're not doing every other year. For homeowners who plan to stay 10 or more years, composite is usually the right call.

What drives the cost

Height is the biggest variable beyond material. Ground-level decks need minimal footings. Elevated decks (over 30 inches off the ground) require engineered footings, ledger bolt connections to the house, and in many jurisdictions a structural engineering sign-off. A second-story deck can cost twice as much as a ground-level one of the same square footage.

Shape adds labor. A simple rectangle is the fastest to build. L-shaped decks, curved edges, and integrated steps all add time and material waste.

Permits and code

Most decks over 200 sq ft or more than 30 inches off the ground require a permit. This is not optional, and an unpermitted deck is a problem at resale. Inspectors flag it and buyers ask for a correction. The permit process also protects you: it ensures footings are properly sized for your local frost depth and load requirements.

If you're in a floodplain (SFHA zone): deck additions may require review from your local floodplain administrator. The design may need to allow water to pass through to avoid diverting flood flow. Check before you start.

Maintenance reality

Pressure-treated wood decks need attention every two to three years: cleaning, sanding, and re-staining or sealing. Skip it for too long and you're accelerating rot at the posts and ledger connection points, which are the most expensive repairs. Composite and PVC largely eliminate this, which is why they've taken over the market in high-humidity climates.

ROI at resale

Deck additions return about 65% nationally, which is solid for an outdoor addition. The return is best in markets where outdoor living matters year-round (coastal California, the Southeast, the Pacific Northwest). In the Upper Midwest where decks sit unused for five months, the return is lower because buyers discount for the short season.