Building codes are on the books of virtually every town, city and county in the nation. But they vary widely from one muncipality to another. ;' If you plan to add a room to your home or convert an existing one, familiarize , yourself with local building codes, says the National Home Improvement Council. As a general rule, a building permit is required whenever structural work is involved or when the basic living area of a residence is to be altered. As an example, if you plan to partition off an unfinished area of your home arid turn it into a room you'd need a building. permit in most localities because you're changing an area from storage to living space. , Code requirements and details on building permits are usually available at your town hall. You simply pay the required fee and assume responsibility for failure to file required permits. Noise restrictions, Sunday work rules, street blockage and clean-up requirements should be carefully noted, as should any electrical or-plumbing or-plumbing needs.