It is becoming increasingly popular among renovators (both owner-occupied and for-profit) to convert existing two- and four-family buildings to single-family homes and townhomes respectively. In order to change the number of units a building, you must have a building permit. During the permit review process, all the appropriate sign-offs are obtained (Cultural Resources office for local historic districts, Zoning Division for conversions, Plan Review for construction and life-safety issues, Plumbing, Mechanical, etc.) from City agencies.

By far the most common method of going about this is to remove the wall between the first floor entry and the second floor front stair. While every building is different, most standard two-family flats (one unit on top, one unit on bottom) will readily accommodate this change. It is relatively common for people to remove additional portions of the wall and install a railing to make the building feel more like a single-family home and less like a "converted" two-family.This is a major change to the building's "character", so if you are applying for historic tax credits, you will have to have your Part 1 application approved before demolition.

Here are some other issues you will confront specific to the conversion process:

• Floor Plan - In most cases, the first floor plan can remain as is. Common alterations include removing the wall between the kitchen and an adjoining room, adding a laundry room, adding a half-bath, and adding a coat closet. In some situations, you will have to completely reconfigure the second floor unit - adding a hallway, adding a master bathroom, adding closets, removing the second floor kitchen, etc.
• HVAC - Even if you intend to keep the existing heating and cooling systems, it is likely that you will have to reconfigure at least the second floor system to acoommodate some floor plan changes.
• Front Door - Since you are converting two units to a single unit, you will be left with an "extra" front door. It is sometimes adviseable to keep it operable for ease of moving furniture up and down the stairway. In local historic districts you will be required to retain the historic "character" of the front facade, which includes the door configuration.
• Rear Stairway - The decision to retain or remove a rear stair if your building has one is often difficult. Balance the convenience of access from the rear bedroom to the kitchen against the potential to gain floor area. It will be a significant cost to remove the stair and frame in the floor, but every square foor counts in some renovations.

As work is performed inspectors visit the site to ensure that the work meets minimum standards and is performed as specified on the drawings. At the end of construction, an occupancy certificate is issued by the building inspector. The inspector verifies that the building is code-complient, measures the rooms, and counts bathrooms.

The permit costs money, and the owner may be required to perform additional work. Unfortunately, some people figure that they can short-circuit the permitting process. They simply cut through the wall between the units and do some reconfiguring upstairs without the city noticing.

The issue comes up when they sell the building to an unsuspecting buyer or do permitted work later. When the inspector comes to issue the occupancy certificate, he or she notices that unpermitted work has been performed on the building (it's hard to hide a big hole in the wall and three bedrooms on the second floor). The city will, in this case, often require that a registered design professional prepare drawings for the conversion after the fact, in effect taking responsibility for the construction that has already been performed. The burden for this falls on the current owner because the occupancy certificate may be withheld. Though one might be able to recover some costs from the seller in the courts, the cost would probably outweigh the architecture fees.

This is frustrating, but a good example of why it is particularly important for an inexperienced buyer to get good advice from a variety of sources and thoroughly research a property before purchasing. Developers must also be conscious of obtaining the appropriate permits [pdf] for any work they perform.