Single-Family vs. Multi-Family in Philadelphia: What the Zoning Code Actually Allows

Written By liza arveladze

If you’ve ever walked through Philadelphia and wondered why one block is full of rowhomes, the next has duplex conversions, and two streets over suddenly has apartments, you’ve run into zoning.

In Philly, the biggest misunderstanding homeowners and investors have is simple:

“If I own a house, can I turn it into apartments?”

The answer is not based on the building.

It’s based on the zoning district.

Philadelphia’s zoning code (Title 14 of the Philadelphia Code) regulates what type of housing is legally allowed on every single parcel in the city, from a small rowhome in South Philly to a large corner lot in West Philly.

Let’s break down what the city actually permits.

First - What Zoning Does

Zoning determines:

  • what you can build

  • how big it can be

  • how many units are allowed

  • parking requirements

  • how tall the building can be

In other words, zoning doesn’t care what you want the building to be; it cares what the land is permitted to hold.
Base zoning districts exist specifically to control what can be built where, and how buildings can be used.

Philadelphia organizes residential properties into several categories:

  • Single-family

  • Two-family (duplex)

  • Multi-family (apartments)

Single-Family Zoning (RSA, RSD)

This is the zoning covering most of Philadelphia’s iconic rowhouse neighborhoods.

What it typically allows

In RSA districts (Residential Single-Family Attached), properties are intended primarily for:

  • one household

  • one dwelling unit

  • one principal use per lot

Rowhomes and townhouses fall into this category. 

Example:

Your typical South Philly rowhome or Fairmount townhouse is almost always RSA zoning.

Important limitations

In these districts, you generally cannot legally convert the home into apartments. Multi-family uses are not permitted unless you obtain a zoning variance.

A common real-world mistake:
Someone buys a house, finishes the basement, adds a second kitchen, and tries to rent it.
From the city’s perspective, you didn’t “add a bedroom.”
You created an illegal dwelling unit.

Typical dimensional controls

(Example RSA-5)

  • ~38 ft max height

  • ~16 ft minimum lot width

These rules exist to preserve the scale and character of rowhouse blocks.

Two-Family Zoning (RTA / RT)

This is the middle category, and one of the most misunderstood.

Here, the property is permitted to contain two dwelling units (a legal duplex).

Typical examples:

  • first-floor apartment + second-floor apartment

  • owner-occupied unit + rental unit

Philadelphia specifically identifies RT districts as housing intended for two families (duplexes).

This is often what homeowners think they have, but many actually live in RSA zoning where it’s not allowed.

Multi-Family Zoning (RM)

Now we get to apartment buildings.

Multi-family zoning (RM districts) allows buildings that contain more than one household living unit.

These districts are specifically intended to support moderate-to-high density residential buildings.

Typical allowed buildings:

  • duplexes

  • triplexes

  • quadplexes

  • apartment buildings

Some RM zones even allow small mixed-use ground-floor commercial space.

There are multiple RM categories (RM-1 through RM-4), mostly differentiated by density and lot area per unit.

For example:

  • minimum lot area per dwelling unit may start around 360 sq ft, depending on project size

This is why a building in West Philly might legally hold four apartments, while an identical building in South Philly cannot.

Why This Matters (The Real-World Consequences)

Zoning determines whether you can:

  • add a second kitchen

  • convert a basement to an apartment

  • build a rental unit

  • sell a property as an “investment property”

  • refinance

  • insure the property

A property advertised as a duplex but zoned RSA is considered an illegal conversion.

Banks, appraisers, and buyers check zoning, and if it doesn’t match the building use, financing can collapse. Be sure to protect yourself in a sale by investigating the zoning. A previous owner’s mistakes become yours to make right when you take over ownership.

The Biggest Philly Confusion: “It Already Has Two Units”

Philadelphia has thousands of properties that were informally converted decades ago.

But zoning follows the legal designation, not the existing condition.

You may see:

  • two mailboxes

  • two kitchens

  • two electric meters

None of that makes it legal.

Only zoning (or a granted variance) does.

Why Philadelphia Uses These Rules

Cities use zoning to balance:

  • neighborhood character

  • infrastructure capacity

  • density

  • parking demand

Lower-density districts generally allow single-family homes, while higher-density districts allow apartments.

Multi-family housing is also a major factor in affordability and walkable neighborhoods because it increases residential density.

Before You Buy, Renovate, or Convert

In Philadelphia, the correct order is:

1. Check zoning
2. Then design

Not the other way around.

A permit set that ignores zoning will be rejected, even if the design itself is perfectly buildable.

The good news:
Philadelphia provides a zoning summary for every address, and a designer or architect can quickly tell you what is possible on a property.

Final Thought

Single-family vs. multi-family housing in Philadelphia isn’t about architecture; it’s about land entitlement.

Two buildings can look identical.
One can legally contain four apartments.
The other must remain a single house forever unless approved by the Zoning Board.

Understanding that difference early is often the difference between a successful project and an expensive mistake.

liza arveladze
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