Do I need a permit for a roof replacement?

Yes — virtually every US municipality requires a permit for a full roof replacement, and ~90% require one for partial replacement covering more than a single slope. Permits run $150–$500 and include an inspection (usually post-tear-off, before underlayment goes down). Unpermitted roof work voids your homeowners insurance for any future leak-related claim AND blocks resale (it'll surface during the buyer's inspection). Some jurisdictions allow a contractor-pulled permit; some require homeowner sign-off; check with your county building department. Reroofs in hail-belt states often require ice-and-water shield + new-code underlayment that wasn't required when the old roof was installed.