What’s the Use? Primary vs. Accessory

By Carolyn Ristau

The Pittsburgh zoning code divides uses into primary and accessory uses and applies different regulations to each type.

Use is defined as:

the purpose for which land or a building is arranged, designed or intended, or for which either land or a building is or may be occupied or maintained. (926.242)

There is not a specific definition in the code for what constitutes a primary use. However, the primary uses recognized by zoning code are listed with the approval path by zoning district in section 911.02. Most sites will have one or more primary uses. Common primary uses include single-unit detached residential (aka single-family homes), restaurant, office, retail sales and service (aka stores), and commercial parking.

Accessory uses are uses, activities, or structures subordinate to the primary use(s) on a site. The base standards for accessory uses are found in Chapter 912. Common residential accessory uses include fences, garages and parking pads, decks (including rooftop decks), sheds, and home occupations (aka working from home).

Some uses, such as parking and agriculture, can be classified as either primary or accessory depending on their intensity and relationship to other uses on a site. Parking that serves just the use on the site is accessory while parking open to anyone is primary. Backyard chickens are an accessory agriculture use while a community garden is a primary agriculture use.

One of the areas where the distinction between accessory and primary uses can get sticky is setbacks. Whether primary or accessory, uses are subject to the setback standards of the zoning district they are in. Setbacks determine the minimum distance between a property line and a use, activity, or structure.

Pittsburgh’s zoning code acknowledges that the setback requirements are often not a good fit for the size and shape of property in the city. Provisions are scattered throughout the code to allow for administrative relief to the base setback requirements under certain conditions. However, these provisions typically apply to either the primary or accessory use, not both.

This can get awkward, especially for rooftop decks. Most residential zoning districts have a minimum 5’ side setback that under certain conditions can be reduced to 3’ or 0’ for the primary use - in this case, a house. This reduction does not apply to accessory structures like the rooftop deck. This means that where a new house can be built to maximize the allowable width on Pittsburgh’s common narrow lot, the rooftop deck is restricted to up to 10’ less. (There are provisions for reducing the width barrier on the deck, but they require more fees and process.)

Another difference between primary and accessory uses is their documentation. All primary uses must be listed on a Certificate of Occupancy. Accessory uses are more fluid when it comes to documentation. Over the decades and administrations, certain accessory uses may have been required to be listed on a Certificate of Occupancy at one time and not at another. This can create an issue when an applicant seeks a permit to repair or replace an accessory use, such as an HVAC unit, that doesn’t meet the current regulations. If there is no paperwork on file showing that it was originally installed in compliance with the regulations of the time, the applicant will need to bring it into compliance, which may involve an expensive and time-consuming zoning board process. 

Applicants can use the City’s Certificate of Occupancy search to see what uses (primary or accessory) are documented for a property to gage if their application may have a use issue. The caveat here is that the certificate(s) may not be filed under the address the applicant uses.