Depending on how your contract is written with the home improvement professional, either you or the contractor will be responsible for securing city or county approval to perform most remodeling jobs.
Building codes set minimum public-safety standards for such things as building design and construction. Codes vary from one county and city to the next, but specialized codes generally exist for plumbing, electricity, and fire. Each usually involves separate inspections and inspectors.
In addition, permits are generally required when any structural work is planned or the basic living space of a home is altered. They generally cover new construction, repairs, alterations, demolition, and additions to a structure.
Some jurisdictions require permits to be posted in a visible spot on the premises while the work is being done. Besides structural changes, permits also may be needed to cover the installation of foundations for tanks and equipment, as well as the construction or demolition of ducts, sprinkler systems, or standpipe systems.
Failing to get the necessary permits can lead to unwanted headaches. At one extreme we've witnessed home owners having to remove a structure from their property at the time of sale due to lack of permits. We've also seen all too often the sale of a home fall through when it was discovered that permits were not obtained adn subsequently that the work done was not to code and cannot be easily corrected.
If you are buying a home and notice changes or an additional to the property, it would be prudent to ask the seller if permits were obtained and to ask for copies. You can also check with the city or county as appopriate for permits.