What’s the cost to build a 300 sq ft deck (DIY vs pro)?

Building a 300 sq ft deck costs about $7,500–$15,000 in pressure-treated wood and $11,000–$23,000 in composite once you include typical railing, a short stair run, and permits. DIYers can source composite materials for roughly $3,000–$8,100 and save most of the labor—provided they handle footings, ledger, code, and inspection correctly.

  • Pro-built price ranges:

    • Pressure-treated (PT) wood: about $25–$50 per sq ft, so $7,500–$15,000 for 300 sq ft (base surface only; rail, stairs, permits extra).

    • Composite: typically $25–$54 per sq ft installed, so $7,500–$16,200 for 300 sq ft (base surface only).

  • DIY materials (composite): roughly $10–$27 per sq ft (decking + substructure + hardware), so $3,000–$8,100 for 300 sq ft (tools/time not included).

  • Add-ons that swing totals: railing (~$40–$80/lf for composite; cable/glass often $80–$150+/lf), stairs (~$25–$50 per step + stringers), permits (≈ $50–$500+ depending on city). 

  • ROI anchor (national averages, 2025): “Deck Addition | Wood” job cost $18,263 with 95% recouped; “Deck Addition | Composite” $25,096 with 89% recouped.

Read more: What deck shape fits an L-shaped house?

What’s the cost to build a 300 sq ft deck

How to estimate a 300-sf deck in 5 straight steps

  1. Choose material (PT wood vs composite).

  2. Calculate surface: 300 × (your installed $/sq ft).

  3. Add railing: perimeter minus house-side; on a 15×20 deck attached to the home, that’s ≈ 50 linear feet (15 + 20 + 15). Multiply by your $/lf.

  4. Add stairs: count steps (height ÷ ~7–7.5" risers) × per-step cost; add stringers if custom.

  5. Add permits + extras: permit fee in your city, plus lighting, fascia, skirting, and any demolition.

Read more: modern deck ideas with low maintenance.

Three realistic 300-sf scenarios (with math)

A) Budget PT wood, ground-level, no railing (DIY vs Pro)

  • Pro build (surface only): 300 × $25–$50 = $7,500–$15,000

  • DIY (materials only): board prices are lower, but once framing, footings, hardware, and consumables are added, many owners still land in the low thousands—and trade time for savings. (You’ll also need tools: circular/miter saw, impact driver, level, PPE.)

  • When this fits: patios or low platforms where code doesn’t force rails; simple rectangles; fast timeline.

Bottom line: cheapest path to a usable deck, but expect stain/seal every 2–3 years and recurring upkeep costs (see ownership section).

B) Mid-spec composite, attached, 3-side railing (~50 lf), one stair run (≈8 steps)

  • Surface (pro): 300 × $25–$54 = $7,500–$16,200

  • Railing (composite): 50 lf × $40–$80 = $2,000–$4,000

  • Stairs: 8 steps × $25–$50 = $200–$400, plus $160–$560 if new stringers.

  • Permit: $50–$500+ depending on locality and whether the deck is attached/elevated. 

Typical total: roughly $9,900–$21,700 depending on finish choices, site, and code requirements (calculated by adding the ranges above).

Read more: Deck: wood vs composite vs stone—pros, cons, cost, maintenance.

C) Premium composite/PVC look with upgraded rail, lighting, planter/bench

  • Benchmark against the 2025 Cost-vs-Value composite “spec deck”: $25,096 for a ~16×20 project (similar in scale to 300–320 sf) including one stair, bench, planter, and composite railing; 89% of cost recouped at resale. Scaling that spec to 300 sf often lands around the low- to mid-$20Ks before big extras (curves, skirting, hidden storage). 

Who chooses this: homeowners prioritizing low maintenance, upgraded looks (matching fascia, picture-frame borders), and stronger resale optics.

DIY vs Pro: where the money actually goes

  • Labor is a large slice: Pro labor typically runs $15–$35 per sq ft (complexity can push higher). For 300 sq ft, labor can easily be $4,500–$10,500 of the total. 

  • DIY savings are real, but remember: layout, ledger attachment, footings, stair geometry, and railing safety are code-critical. Mistakes can erase savings (or fail inspection).

  • Tools/time: if you don’t own a miter saw, impact driver, levels, digging gear (auger/post-hole digger), joist tools, PPE, etc., count rentals and learning time.

  • Warranty & liability: pros typically include workmanship warranties and carry insurance; you also avoid rework if the municipality red-tags the deck.

DIY composite materials reality check: Trex’s own estimator shows $10–$27/sq ft for a complete materials package (decking, substructure, hardware/fasteners). For 300 sq ft, that’s $3,000–$8,100 before rails/stairs/permitting. 

Read more: Which deck material stays coolest in summer?

Material options & per-sq-ft reality (2025)

  • Pressure-treated wood (PT): $25–$50/sq ft installed; inexpensive upfront, most upkeep over time. 

  • Composite: $25–$54/sq ft installed (materials: $12–$22/sq ft; installed includes labor/overhead). Lower upkeep, higher curb appeal to many buyers.

Quick comparison for 300 sq ft (base surfaces only)

Option

Installed $/sf

Base Surface (300 sf)

Typical Railing Add (50 lf)

Stairs (8 steps + stringers)

Permit (typical)

PT wood

$25–$50

$7,500–$15,000

$750–$1,500 (wood ~$15–$30/lf)

~$360–$960

$50–$500+

Composite

$25–$54

$7,500–$16,200

$2,000–$4,000 (composite ~$40–$80/lf)

~$360–$960

$50–$500+

Railing, stair, and permit figures summarized from 2025 cost guides

Read more: Which deck material stays coolest in summer?

Add-ons that move the needle (and why)

  • Railing: Safety + code + aesthetics. Typical composite rail runs $40–$80/lf; wood is often $15–$30/lf; metal $50–$100/lf; specialty cable or glass usually $80–$150+/lf and can hit $270/lf depending on system/complexity.

  • Stairs: Count by actual risers—more elevation = more steps + more structure. Expect $25–$50 per step, plus stringers if not prefab. 

  • Lighting, fascia, and skirting: small individually, big in aggregate; budget a few hundred to a few thousand depending on design/lengths.

  • Demolition (if replacing): older tear-outs add $5–$15/sq ft and disposal. 

10-year cost of ownership: Wood vs Composite

  • Wood maintenance cycle: plan to refinish/stain every 2–3 years. Pros commonly charge $550–$1,250 per visit (roughly $1–$4/sq ft). Over 10 years, that’s 3–5 cycles = ~$1,650–$6,250 just for upkeep. 

  • Composite maintenance: mostly washing (garden hose/soap) plus occasional deeper clean; if you hire a pro, pressure washing is about $100–$250 per service. 

Takeaway: Composite’s higher day-one price often narrows (or wins) over a decade thanks to fewer paid maintenance cycles.

Read more: Deck Maintenance & Care Checklist for DIYers

Resale value & “feel-good” factor

The 2025 Cost-vs-Value report shows “Deck Addition | Wood” recoups ~95%, while “Deck Addition | Composite” recoups ~89% on average. Either way, decks score very well for resale in 2025—which helps justify upgrading railings, lighting, or fascia when budget allows. 

Regional pricing & how to localize your estimate

  • Use a brand calculator to price materials for your exact size and railing length (Trex has a quick estimator). Pair that with a big-box calculator to verify quantities. Then get 2–3 local bids to lock in labor and permitting. 

  • Expect higher labor for frost footings, hillside sites, remote access, or second-story decks—your city’s code and soil drive real-world cost spread. 

FAQs

Do I need a permit for a 300-sf deck?

  •  If it’s attached or elevated, most municipalities require a permit. Fees vary widely—about $50–$150 in some places and $230–$500 (or more) in others. Always check your local building department and HOA rules before you buy materials. 

How much railing do I need for a 15×20 deck?

  • If it’s attached to the house along the 20-ft side, you typically rail three sides: 15 + 20 + 15 = 50 linear feet. Multiply by your chosen rail system’s $/lf to estimate.

How do stairs change cost?

  • Count risers. A single 8-step run adds ~$200–$400 for steps plus $160–$560 if you need stringers; complex stairs, landings, or metal components increase cost. 

Can I really save money with DIY?

  • Yes—especially on a simple ground-level build. For composite, materials for 300 sf can run $3,000–$8,100; a comparable pro build often totals $7,500–$16,200 before rails/stairs. The delta is mostly labor—but pros bring speed, code compliance, and warranty.

What’s a smart, mid-budget target for 300 sf with rails and a short stair?

  • Using the mid-spec scenario above, many projects land around $12K–$18K, but region, material tier, and design details (fascia, picture-frame borders, lighting) push you up or down. Cross-check your local numbers with the Trex estimator and at least two contractor quotes. 

“Total deck cost = (Area × Installed $/sf) + (Railing lf × $/lf) + (Steps × $/step [+ stringers]) + Permit + Extras (fascia, skirting, lighting, demolition).
For a 15×20 deck attached to the house (50 lf rail, ~8 steps), plug in the ranges above to produce a low and high estimate for your market.”

Final take

If you’re optimizing for lowest upfront cost, PT wood at ground level wins (with maintenance tradeoffs). If you want low-maintenance + strong resale, composite delivers—and the 2025 data shows both wood (95%) and composite (89%) decks hold value exceptionally well this year.

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Tanzite Stonedecks – Premium, High-Performance Stone Decking

Founded in January 2020 in Alberta, Canada, Tanzite Stonedecks offers scratch-resistant, fireproof, fade-proof, and stain-proof decking. Developed and tested in Canada, our stone decks install on standard composite framing, making them ideal for decks, stairs, ramps, rooftops, and patios. Tanzite’s Appalachian and Rainier collections are crafted for long-lasting beauty and minimal maintenance. Serving the U.S. and Canada, Tanzite decks are the perfect choice for outdoor living – durable, stylish, and built to last.