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.
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Pro-built price ranges:
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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).
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Composite: typically $25–$54 per sq ft installed, so $7,500–$16,200 for 300 sq ft (base surface only).
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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).
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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).
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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?
How to estimate a 300-sf deck in 5 straight steps
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Choose material (PT wood vs composite).
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Calculate surface: 300 × (your installed $/sq ft).
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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.
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Add stairs: count steps (height ÷ ~7–7.5" risers) × per-step cost; add stringers if custom.
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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)
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Pro build (surface only): 300 × $25–$50 = $7,500–$15,000.
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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.)
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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)
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Surface (pro): 300 × $25–$54 = $7,500–$16,200.
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Railing (composite): 50 lf × $40–$80 = $2,000–$4,000.
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Stairs: 8 steps × $25–$50 = $200–$400, plus $160–$560 if new stringers.
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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
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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
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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.
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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).
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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.
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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)
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Pressure-treated wood (PT): $25–$50/sq ft installed; inexpensive upfront, most upkeep over time.
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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)
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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.
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Stairs: Count by actual risers—more elevation = more steps + more structure. Expect $25–$50 per step, plus stringers if not prefab.
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Lighting, fascia, and skirting: small individually, big in aggregate; budget a few hundred to a few thousand depending on design/lengths.
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Demolition (if replacing): older tear-outs add $5–$15/sq ft and disposal.
10-year cost of ownership: Wood vs Composite
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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.
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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
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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.
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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?
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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?
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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?
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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?
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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?
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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.
