How Much Does a 20x20 Deck Cost in Tennessee?
A 20x20 deck — 400 square feet — is the most common size request we see in Lawrence and Giles County. It's large enough for real outdoor living use, small enough to be achievable for most homeowners, and fits most residential house footprints. If you're pricing a deck this size in Lawrenceburg or Pulaski, here's what it actually costs and why the quotes you're getting vary the way they do.
A completed permitted deck in Middle Tennessee — properly flashed ledger board, concrete footings, and pressure-treated framing built to code.
Quick answer: 20x20 deck cost in Middle Tennessee
A 20x20 deck (400 sq ft) in Lawrence or Giles County runs $18,000 to $30,000 installed in 2025. Pressure-treated lumber at standard height is $18,000–$24,000. Composite decking with upgraded railing runs $26,000–$34,000. Height off grade, stair configuration, and site access determine where on that range you land.
What makes the price move on a 20x20 deck
Material choice
The substructure — posts, beams, joists, ledger — is pressure-treated lumber regardless of what surface material you choose. The surface boards are where the cost difference lives. Pressure-treated surface boards on a 20x20 deck cost $2,800–$4,200 for materials; composite (Trex, TimberTech) runs $5,000–$9,000 for the same square footage. That difference is meaningful but not as large as some homeowners expect — the labor is the same either way.
Height off grade
A deck that sits 18–24 inches off grade has shorter posts, simpler beam sizing, and straightforward stair work. A deck that's 4–6 feet off the ground — common on homes with a walk-out basement or a sloped lot in Lawrenceburg — requires larger posts, heavier beams, and more substantial temporary shoring during framing. Every additional foot of deck height adds cost. We measure this during the site visit and factor it into the quote.
Stair configuration
A single stair run off one end of a 20x20 deck is standard. A deck with two stair runs, a switchback stair, or a stair landing area costs more — both in materials and labor. If you're planning to use a stair from the deck to a patio or to a yard at a significantly different grade, we plan the stair geometry during the design phase to make sure it's safe and code-compliant.
Railing style
A standard pressure-treated 2x2 baluster railing system is included in our base pricing. Upgrades to cable railing, horizontal composite rail systems, or custom railing designs add $2,000–$6,000 to a 20x20 deck depending on linear footage and style. Railing is the single biggest cosmetic upgrade on a deck and the one that most visibly changes the appearance of the finished project.
| Scenario | Lawrence / Giles County estimate |
|---|---|
| 20x20 PT lumber, standard height, one stair run | $18,000 – $23,000 |
| 20x20 PT lumber, elevated (4 ft), two stair runs | $22,000 – $30,000 |
| 20x20 composite surface, standard height | $24,000 – $32,000 |
| 20x20 composite, cable railing, elevated deck | $30,000 – $42,000 |
What's included in our 20x20 deck quote
Every ACS deck quote covers: permit application and inspections, concrete footings, post-to-beam framing, ledger installation with proper flashing, joist system with metal joist hangers at every connection, decking surface installation, baluster railing system, and one stair run. What isn't included unless specified: upgraded railing styles, additional stair runs, built-in benches or planters, and deck lighting.
Permits for a 20x20 deck in Lawrence and Giles County
Every deck we build is permitted. The permit process for a 20x20 deck in Lawrence or Giles County involves submitting a site plan showing deck location and dimensions, footing layout and depth, ledger connection detail, and railing height. Two inspections follow: footing inspection before concrete is poured and framing inspection before decking is installed. We handle this completely — you don't visit any permit office and you don't deal with the inspector directly.
Frequently asked questions
How much does a 20x20 deck cost in Tennessee?
$18,000–$30,000 for most configurations in Lawrence and Giles County. Pressure-treated at standard height starts around $18,000. Composite with elevated design and upgraded railing can reach $34,000+. Site visit required for a firm number.
How many footings does a 20x20 deck need?
Typically 6–9 footings depending on beam span design. We design the footing layout during the permit application. Each footing extends below the 12-inch Tennessee frost line with a widened bell at the bottom.
Is a 20x20 deck big enough?
400 sq ft is comfortable for a 6-person dining set plus a grill and circulation. For frequent larger gatherings or a separate seating area, a 20x24 or 24x24 gives more flexibility. We discuss intended use during the site visit.
Does a 20x20 deck need a permit in Tennessee?
Yes — any attached deck requires a building permit. We handle permits and inspections on every deck we build. Skipping the permit creates real risks at home sale and in insurance claims.
How long does it take to build a 20x20 deck?
4–6 days to build once permits are approved. Permit review typically runs 2–3 weeks for a complete application. Total timeline from contract to finished deck is 4–6 weeks.
Get a free estimate on your 20x20 deck in Pulaski, Lawrenceburg, or Middle Tennessee. Call (931) 369-2134 or request a quote online. See our deck construction service page, our local deck cost guide, and our post on why permits matter on deck projects.