Do I need a permit to build a deck?

In most US jurisdictions, yes — if the deck is over 30 inches above grade, over 200 sqft, or attached to the house. Permits typically cost $150–$700 and require a contractor (or owner-builder) submitted drawing showing footings, joist spacing, and post layout. Skipping the permit voids your homeowners insurance for any deck-related claim, blocks resale (it'll show up as unpermitted work in the inspection), and exposes you to fines + forced removal. Some homeowner-friendly states (Texas, Tennessee, Indiana) allow owner-builder permits on residential property. Check your county building department site before starting — rules vary by city, not just state.