If you’ve ever struggled to determine whether a building should be classified as a single-family home, duplex, townhouse, or apartment, and which fire sprinkler standard applies (NFPA 13D, NFPA 13R, or NFPA 13), you’re not alone. Classifying residential occupancies and selecting the correct sprinkler standard can be confusing, even for experienced contractors and code professionals.

In this blog, we’ll break down the differences between residential building types and explain when NFPA 13D, NFPA 13R, or NFPA 13 applies,  so you can design and install the correct fire sprinkler system with confidence.

Three disclaimers here:

• This blog only addresses residential-type housing where people live on a permanent basis – like single family homes, duplexes, townhouses, and apartments. It won’t address housing that is transient in nature – like hotels, short-term rentals, or board and lodging – and it won’t discuss other types of housing – like dormitories, barracks, fraternities, sororities, or board and care facilities.
• Since it only deals with residential type occupancy, this blog also won’t address institutional-style occupancies where some or all of the occupants cannot escape without assistance.
• Many states and local communities amend the codes for residential occupancies so it is always best to check with the appropriate code official – in this case, it is usually the building official.

Types of Residential Housing

First, we will identify the characteristics of various types of housing.

Single family homes are the most common residential type of housing. They typically sit on their own separate property lot. While it is possible to have other buildings on the lot – sometimes called accessory dwelling units (ADU) or detached garages – usually a single-family home sits alone on the lot (not counting sheds). Generally speaking, the same person or entity owns the land and the home. The applicable construction code is typically the International Residential Code (IRC).

Duplexes are basically two single family dwellings that are attached to each other. They are often on the same property lot together although that is not a requirement; they could be on separate lots. The dwellings cannot share anything except a common fire-rated wall between them. They will have separate utilities, egress components, and addresses. The applicable construction code is generally the IRC.

Figure 1 – Townhomes

Townhouse arrangements start to get more complicated. There are many names given to this type of housing: attached townhouses, detached townhouses, rowhouses, townhomes, triplexes, quad homes, etc. Typically, townhouses are three or more attached residences under the same roof, each on a separate property lot (with property lines between), having separate utilities, egress components, and addresses.

Figure 2 – Six-Unit Townhouse

Townhouses are typically owned by the residents (although some can be rental units). Ownership of the townhouse extends from the ground to the roof. Hence, stacked townhouses are not typically allowed (see section on condos later). Townhouses are often part of a larger development with shared amenities – like roads, parks or trails – and each townhouse owner pays homeowner association fees.

When constructed in accordance with the IRC, townhouses have to be open on at least two sides of the structure. Figure 2 shows townhouses with property lines (shown in blue) and each unit is open on at least two sides.

Having two open side is problematic where there are more than four “back-to-back” homes as the center ones will only be open on one side.

Figure 3 – Back-to-Back Townhouse Complex

Figure 3 shows a 6-unit townhouse arrangement where the inside units (Units B and E) are only open on one side. Townhouses that are only open on one side typically need to be constructed in accordance with the International Building Code (IBC).

Apartment buildings share many features. They often have shared vehicle parking, shared entrances, stairs, elevators, and hallways providing access to the individual units, common utilities, communal recreation or social areas (fitness, swimming, party rooms, etc.), and laundry facilities. The applicable code is the IBC, and these carry an occupancy classification of R-2.

Earlier, the term condos (or condominiums) was mentioned. Condos refer to an ownership type and not a different type of residential housing itself. Condos are typically single units within a larger building, where residents own the individual units but share ownership of common areas and facilities, like laundry rooms, lobbies, hallways, elevators, fitness spaces, and swimming pools. With a condo, individuals own the interior of their living unit. The building’s exterior and common areas are jointly owned by the residents and typically managed by a homeowners’ association.

The codes and standards are not concerned with ownership. They recognize that fire behaves the same whether the building is owned by one person or many people. From a code standpoint, these are R-2 occupancies (the same as apartment buildings).

NFPA 13, NFPA 13R, or NFPA 13D? Which Fire Sprinkler Standard Applies?

The applicable fire sprinkler standard for single family dwellings and duplexes is NFPA 13D, “Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes”. While the name suggests that its application is limited to single family homes and duplexes, the scope was changed a few editions ago to make it applicable to townhouses that are fire separated from each other. Section 1.1 of NFPA 13D states: “1.1.1 This standard shall cover the design, installation, and maintenance of automatic sprinkler systems for protection against the fire hazards in one- and two-family dwellings, manufactured homes, and townhouses.” (emphasis added).

There is also a sprinkler installation in the International Plumbing Code (IPC) called P2904. It is recognized as being equivalent to NFPA 13D.

As indicated above, townhouses can also be sprinkler-protected in accordance with NFPA 13D. Some jurisdictions also allow townhouses to be protected in accordance with NFPA 13R even though utilities (including sprinkler systems) are not supposed to cross property lines. Sometimes, it can be more cost-effective to install an NFPA 13R system in a townhouse building.

Either NFPA 13R or NFPA 13 can be used for apartment buildings (R-2 occupancies). The model building and fire codes allow some flexibility (code equivalencies) when NFPA 13R is used and many more allowances when NFPA 13 is used as the installation standard.

Summary: NFPA 13D vs 13R vs 13: How to Choose the Right Sprinkler Standard for Residential Occupancies

The classification of residential occupancies can be confusing as can applying the proper fire sprinkler installation standard. NFPA 13D is appropriate for single family homes, duplexes, and townhouse buildings.

In some cases, the AHJ might also allow townhouses to be protected with an NFPA 13R system but that should not be assumed to be the case. Contractors should always ask first.

Apartment buildings share common areas and the applicable fire sprinkler standards are NFPA 13R or 13. NFPA 13 provides far more design alternatives and contractors should inquire before assuming that NFPA 13R can be used.