* Seek information from the staff of the Historic Preservation Division, D.C. Department of Consumer and Regulatory Affairs (614 H Street, NW, Suite 305; 727-7360) to determine if your building qualifies as a "certified" historic structure. Ask for copies of the Historic Preservation Certification Application and related brochures.
* Read the rules by getting a copy of the secretary of the interior's Standards for Rehabilitation and Guidelines for Rehabilitating Historic Buildings from the city preservation office. Read them carefully.
* Take photographs to document the condition of your building before beginning any work. Only photographs can prove that there's nothing of significance to save. Buildings have been denied certification because of the lack of "before" photos.
* Get approval for all work from the local preservation office and the U.S. Park Service before starting work. It's easier to make changes in plans than in the completed work.
* Get help from accountants, lawyers, architectural historians. The D.C. historic preservation office can suggest when consultants will be helpful and can provide you with a list of names. If the tax credit is worth something to you, then it's wise to pay for professional advice beforehand. These advisers can also keep you informed of changes in tax laws and procedures, which often occur.