Madison deck questions
Who builds the deck?
An independent builder you hire directly. This is a Madison-area referral site, so we pass your request along; we do not build, price or guarantee anything.
Do I need a permit in Madison?
Yes. The City of Madison says you need a permit to build a deck. Most decks under 250 square feet cost $75, and the city can issue the permit on the spot if the plans meet code.
Can I replace boards myself without a permit?
In Madison, yes, if the cost is under $500. Work on stairs, joists, beams, columns or guardrails needs a permit or a check with Building Inspection.
How close to the lot line can I build?
In Madison, decks under three feet can reach the lot line in most cases. In Sun Prairie, decks up to 3 feet may come within 8 feet of the rear line, and taller ones must stay 24 feet back.
How deep are Madison deck footings?
At least 48 inches, according to the city, to prevent frost heaving. An inspector checks the holes before the footings go in.
Frost, footings and the inspection
Madison says deck footings must be at least 48 inches deep to prevent frost heaving, and that you schedule an inspection after digging the holes and before installing the footings. Middleton and Fitchburg also inspect footings before concrete.
The state appendix adds detail: concrete of at least 3,000 psi, each post over the middle third of its footing, and a footing within 5 feet of the house wall set at the same elevation as the house footing.
Sources: City of Madison Development Services Center, Decks · City of Middleton, Building Inspections & Building Permits · City of Fitchburg Building Inspection, Permit Requirements · Wisconsin Uniform Dwelling Code, SPS 325 Appendix B. Checked November 9, 2026. Confirm current requirements with your building inspector.