Permit guide · Deck
Do You Need a Permit for a Deck?
Almost certainly yes. Attached decks require a permit in virtually every jurisdiction in Illinois, Wisconsin, and Indiana. Even freestanding decks need permits if they're over 30 inches above grade or exceed 200 square feet. Decks involve structural engineering, frost-depth footings, and specific fastener requirements, and the inspections are strict.
This guide covers
- Footings
- Ledger details
- Rails
- Inspection path
The short answer
If your deck is attached to your house, you need a permit. If it's freestanding but more than 30" off the ground or over 200 sq ft, you almost certainly need a permit. The building department will check footing depth, ledger board attachment, joist sizing, railing height, and stair dimensions. Deck collapses are a leading cause of residential structural failures, which is why inspections exist.
What your jurisdiction checks
Footings & Frost Depth
Every deck post must sit on a footing that extends below the frost line. In Illinois, that's 42 inches deep. In Wisconsin, 48 inches. In Indiana, 36-42 inches depending on the county. Footings are typically 16-24" diameter concrete piers poured on undisturbed soil. This is inspected before you can pour concrete.
Ledger Board Attachment
The ledger board connects your deck to your house, and improper attachment is the #1 cause of deck collapses. Code requires lag bolts or through-bolts (not screws or nails) at specific spacing patterns. Flashing between the ledger and house siding is mandatory. You cannot attach a ledger to brick veneer alone, cantilevered floors, or engineered I-joists without manufacturer approval.
Structural Framing
Joist size, beam size, and post size all depend on span distances, spacing, lumber species, and grade. The IRC provides span tables (R507), but your AHJ may have adopted a different edition with different values. Post-to-beam connections must use approved hardware, not toe-nailing.
Guards & Railings
Required when the deck surface is more than 30 inches above grade. Minimum 36 inches tall (some jurisdictions require 42"). Balusters spaced no more than 4 inches apart (the "sphere test"). The top rail must resist 200 lbs of concentrated force.
Stairs
Maximum 7-3/4" rise per step, minimum 10" tread depth, minimum 36" width. Handrails required at 34-38" height with a graspable profile. Landings required at top and bottom.
Setbacks & Zoning
Decks usually must meet the same setbacks as your house. Some AHJs allow reduced setbacks for uncovered decks. Deck area may count toward lot coverage/impervious surface limits.
The Inspection Sequence
Most AHJs require three inspections for decks: a footing inspection (holes dug to depth, before concrete), a framing inspection (structure complete, before decking installed), and a final inspection (everything complete including railings and stairs).
State-specific notes
Illinois
IL
Follows IRC with local amendments. Chicago has its own building code (not IRC-based). Most suburban AHJs use 2018 or 2021 IRC. 42" frost depth statewide.
Explore Illinois permit rulesWisconsin
WI
UDC (SPS 320-325) applies statewide for 1-2 family dwellings. 48" frost depth statewide, the deepest in the Permitech service area. State-controlled inspector licensing.
Explore Wisconsin permit rulesIndiana
IN
No statewide residential building code. Each AHJ adopts its own (most use IRC 2012 or 2018). Frost depth varies 36-42" by county. Check your specific jurisdiction.
Explore Indiana permit rules
Common deck permit mistakes
- Attaching the ledger board over siding instead of removing siding and flashing properly
- Using deck screws instead of structural bolts for the ledger connection
- Not digging footings to the full frost depth
- Exceeding joist span tables (undersized lumber for the span)
- Missing railings on elevated sections (any surface > 30" above grade)
Start with a free permit check
Enter the address and project so Permitech can identify the permit office, check property context, and research official local sources. Review what we find before deciding whether you want help organizing or filing the permit.
What the free check does
- Step 1: Resolve the propertyMatch the address to its parcel, zoning context, and responsible permit authority.
- Step 2: Research the projectCheck deck requirements against official local sources.
- Step 3: Review the resultSee the permit path first, then decide whether you want help organizing the package or filing it.
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