20×12 Deck Cost in Illinois
A 20×12 (240 sqft) deck in Illinois costs $12,000-$19,200 in mid-tier composite with the state's 1.00× labor multiplier (Midwest). A 12×20 deck (240 sqft) is a long, narrow deck — common for ranch-style homes with a long back wall. Illinois labor 1.00× national (Midwest baseline). Chicago's permit process is more involved than downstate.
5 finish tiers — 20×12 in Illinois
National $/sqft × Illinois's 1.00× labor multiplier × 240 sqft = total installed cost. Materials + labor + standard railing included.
Excludes permit ($131-$324 typical in Illinois), demolition (if replacing), and exceptional framing for 42″ frost depth. Chicago metro permits $250-400. Frost depth 42″ across most of state.
20×12 framing notes for Illinois
Illinois considerations
Get a precise quote for your 20×12 deck in Illinois
Open the Deck Cost Calculator with IL pre-selected and dial in your exact size, framing, material, and railing choices.
FAQ — 20×12 deck in Illinois
How much does a 20×12 deck cost in Illinois?▾
In Illinois, a 20×12 (240 sqft) deck costs $6,000-$9,600 in pressure-treated, $12,000-$19,200 in mid-range composite (Trex Transcend / Fiberon Sanctuary), and $18,000-$26,400 in luxury composite/PVC (TimberTech AZEK / Trex Signature). Numbers reflect Illinois's 1.00× labor multiplier on 2026-Q1 retail.
What's the cheapest way to build a 20×12 deck in Illinois?▾
Cheapest = ground-level pressure-treated pine with no railings (where exempt under 30″ height) — ~$4,800-$7,200 in Illinois. Add stairs + railings + above-grade framing and the build goes to ~$6,720-$9,600. DIY saves 30-50% on labor but requires permit + inspection coordination yourself.
How long does it take to build a 20×12 deck in Illinois?▾
Permit timeline in Illinois: 2-6 weeks depending on jurisdiction. Construction time for a 20×12: pro crew = 5-8 days for framing + boards + railings + stairs. DIY = 3-5 weekends for experienced DIYer. Allow extra time for permit approval + inspections.
What framing do I need for a 20×12 deck in Illinois?▾
IRC R507-compliant framing for a 20×12 deck typically uses 2×8 joists at 16″ OC for spans up to 12 ft, 2×10 joists for spans 12-16 ft. Illinois's frost depth is 42″ — footings must extend below that per IRC R403.1.4. Sonotube 10-12″ diameter at 42″ depth is typical. Verify with your local building department.
Is composite worth it for a 20×12 deck in Illinois?▾
Over 25 years in Illinois: PT pine = ~$7,200 install + ~$15,000 maintenance (stain every 2-3 yr) = $22,200 total. Mid composite = ~$13,920 install + $0 maintenance = $13,920 total. Composite wins by 59-81% over 25-yr lifecycle PLUS better resale value in Illinois's market.