(This is a continuation of "Why Should I Care About Building Permits?", so please read that first if you have found your way here through another link.)
Building permit requirements vary by state and even by city and county, so please keep in mind that this post is geared toward homeowners in North Carolina, and laws will differ for those living in other states.
You need a building permit to:
◘ Build, re-construct, alter, move, remove or demolish any building (with some exceptions for small storage sheds, according to their size), including constructing, adding onto, or altering any external or load-bearing structures on an existing building.
This includes adding onto, changing, or repairing any exterior wall or other load bearing wall, floor joists and footings, replacing any wood in a roof (including plywood, beams, and rafters), replacing one type of shingles or roof covering with another (asbestos shingles to fiberglass shingles or metal roofing), adding new shingles over existing roofing material, and building a deck or porch.
◘ Install, expand, extend, or repair any plumbing system (there are certain exceptions to plumbing permits for replacing a hot water heater, but both require a licensed contractor to install them, because of requirements for inspection and a leak test on the piping for gas heaters and for the electrical work on electric water heaters).
◘ Install, replace, add to, or change the design and components of a heating and cooling system (swapping an electric furnace for gas, , re-routing duct work, or adding duct work to heat and cool an additional room, for example), and for any repair costing more than $5,000.
◘ Install, extend, alter, or repair any electrical wiring, device, appliance, or equipment. The few exceptions to this (repairing or replacing an outlet or light switch) still require that the work be performed by a licensed electrician, in the same location, and operate on the same or less power than the previous fixture. This includes installing light fixtures, hard-wired outdoor or carport lighting, ceiling fans, and attic fans.
◘ Have any construction, alterations, repairs, or additions done on a commercial or rental property. Also, if you are a landlord or property owner, you must have the work done by a licensed professional, not yourself.
You do not need a building permit to :
◘ Do any project in a single-family residence or farm building costing less than $5000, unless the work adds to, replaces, or changes load-bearing structures, plumbing, heating, air conditioning, or electrical wiring, devices, appliances, or equipment; uses materials not allowed by the NC Uniform Residential Building Code, repairs a load-bearing structure, or adds roofing materials.
◘ Add interior walls or add an opening or doorway to a non load-bearing interior wall.
◘ Install, replace, or repair siding on a home.
◘ To replace existing pluming piping or fixtures with like fixtures (replacing a sink, toilet, or appliance), so long as the water supply lines and the trap in the drain line are not altered.
◘ Repair or replace most heating and air conditioning equipment and components, so long as the design or type of system is not changed.
◘ Replace an existing light switch or receptacle with one of the same voltage and the same or lower amperage, so long as the work is done by a licensed electrician and in compliance with State Building Code and State Electrical Code.
◘ Add an outdoor storage shed or other "accessory building", in some jurisdictions, so long as it is not wired for electricity, and does not exceed maximum size limits (12 ft in any dimension for many NC counties).
If you are not sure whether or not you may need a building permit, the best thing to do is to find out from the source. Call your city or county inspection department, or the inspections division of your local planning department, and they will tell you which permits you may need, if any. It is much better to check in advance than to have to pay a fine for a retroactive permit, or tear down the work you have done because it is out of compliance.
Some jurisdictions are very strict, and may even have additional requirements to be met, while others are lax and may allow certain repairs without a permit, but it is always better to find out what your local inspector requires rather than to get caught partway through a project and find out you needed a permit, or need to change something in order to keep it.