Deck cost calculator for Illinois

How much does a deck cost in Illinois?

A 16 × 12 foot composite deck, 192 square feet with railing and a short flight of stairs, costs $7,190 to $9,730 installed in Illinois, or about $44.07 per square foot. The same deck in pressure-treated pine runs $5,660 to $7,660, in cedar $6,330 to $8,560, and in PVC $7,560 to $10,230.

Illinois labor runs about 5% above the national average, which shifts that composite deck up by roughly $465 against a national-average build. Labor is 40-50% of an installed deck, and it climbs further on elevated or complex-shaped decks where framing takes longer.

Building it yourself removes the labor line: the same composite deck comes to roughly $6,251 in materials, hardware, permit and tool rental. Decks are more forgiving DIY projects than fences in one respect and less in another. The framing is straightforward, but the ledger connection to the house is the single most safety-critical detail in residential construction, and it is the most common inspection failure.

What common deck sizes cost in Illinois

Most people arrive at this deck calculator with a size already in mind, so here are the four that get searched most, priced for Illinois. A 12 × 12 deck (144 sq ft) costs about $6,814 in composite. A 14 × 20 (280 sq ft) costs about $11,413, a 16 × 20 (320 sq ft) about $12,716, and a 20 × 20 (400 sq ft) about $15,322.

In pressure-treated pine those same footprints come down sharply, the 16 × 20 to $9,711 and the 20 × 20 to $11,566. That is the single largest saving available on any deck in Illinois.

Notice how little the per-square-foot figure moves between sizes: $40.76 on the 14 × 20 against $38.31 on the 20 × 20. The permit, the ledger and the stairs cost the same whatever the area, so they spread thinner as the deck grows. If you are undecided between two sizes, the larger one is almost always the better value per square foot.

Building a deck in Illinois

Illinois has a deep 42-inch frost depth that adds real concrete and labor to every post. Deck footings have to reach below that line, and on a 16 × 12 deck that is six to nine footings, so frost depth drives the substructure budget more than any decking choice does.

The climate here is continental, with genuinely cold winters and hot humid summers, and ground conditions are deep prairie loam over clay, generally easy to dig but slow to drain. In practical terms: Freeze-thaw and snow load both govern; footings must reach 42 inches, which is often half the substructure cost.

Air-entrained mix and a 42-inch footing depth are both non-negotiable for exterior work in the Chicago area. That matters for a deck because every footing is a small concrete pour, and the same constraints that govern a slab govern the piers under your deck.

Composite and Trex decking in Illinois

Composite is the most common upgrade from pressure-treated pine here, and the reason is maintenance rather than price: it never needs sealing, which matters in a climate that is continental, with genuinely cold winters and hot humid summers. The composite deck calculator setting above prices boards at $9 per square foot, framing at $5 and installed labor at $10 before the Illinois multiplier of 1.05× is applied.

Trex is the brand most people mean when they say composite, and it is sold in tiers rather than at one price: Enhance Basics runs around $5 per square foot for boards alone, Select around $9, and the premium Transcend line around $12. TimberTech, Fiberon and Deckorators compete at each of those tiers. Whichever brand goes down, the framing, railing and labor underneath are identical, which is why installed totals differ far less than board prices suggest.

Freeze-thaw and snow load both govern; footings must reach 42 inches, which is often half the substructure cost. Weigh that against how long you plan to stay: over 25-30 years of service the composite deck above works out to $308 per year in Illinois against $533 for pressure-treated pine.

Deck permits and inspections in Illinois

Chicago requires permits for most fences and all decks, and enforces a 5-foot front-yard height limit. Suburban villages frequently add their own design review.

Deck permits cost more than fence permits almost everywhere because structural review is involved. Our estimate carries $368 as a permit and inspection allowance for Illinois. Expect at least two inspections: one on the footings before concrete is placed, and one on the framing before decking goes down.

Do not skip the permit on a deck. An unpermitted deck surfaces during resale, and lenders and insurers both take an interest. Rebuilding a deck to code after the fact costs far more than permitting it correctly the first time.

How we calculated these estimates

Every figure on this page comes from the same open formula the calculator above uses. We start from a 2026 national baseline for materials and installed labor, apply the state labor multiplier published by the Bureau of Labor Statistics for construction trades, then add the line items your inputs call for: gates, corners, removal, permits and a waste allowance. Nothing is hidden behind a lead form, and no contractor pays us to appear here. The result is a planning range, not a quote. The low figure assumes straightforward access and an efficient crew, and the high figure assumes obstacles, difficult access, or premium material grades.