Common Walls that Separate Townhouses

[jar546]

Some significant changes can be found in the newest version of the IRC. At the end, some reasoning as to why the changes were made can be found.

R302.2.2 Common walls.
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Common walls separating townhouse units shall be assigned a fire-resistance rating in accordance with Item 1 or 2 and shall be rated for fire exposure from both sides. Common walls shall extend to and be tight against the exterior sheathing of the exterior walls, or the inside face of exterior walls without stud cavities, and the underside of the roof sheathing. The common wall shared by two townhouse units shall be constructed without plumbing or mechanical equipment, ducts or vents, other than water-filled fire sprinkler piping in the cavity of the common wall. Electrical installations shall be in accordance with Chapters 34 through 43. Penetrations of the membrane of common walls for electrical outlet boxes shall be in accordance with Section R302.4.

1. 1.Where an automatic sprinkler system in accordance with Section P2904 is provided, the common wall shall be not less than a 1-hour fire-resistance-rated wall assembly tested in accordance with ASTM E119, UL 263 or Section 703.2.2 of the International Building Code.
2. 2.Where an automatic sprinkler system in accordance with Section P2904 is not provided, the common wall shall be not less than a 2-hour fire-resistance-rated wall assembly tested in accordance with ASTM E119, UL 263 or Section 703.2.2 of the International Building Code.

Exception:Common walls are permitted to extend to and be tight against the inside of the exterior walls if the cavity between the end of the common wall and the exterior sheathing is filled with a minimum of two 2-inch nominal thickness wood studs.

REASONS:
Correlation with proposed changes to the IRC to clarify use of the term “townhouse” in both codes. In the IBC, there are currently eight uses of the term “townhouse,” including three in the preamble. If this change is approved, it will be necessary to editorially revise only one of those current occurrences, the one in Section 2308.1, which will need to be revised as follows to use the term “townhouse unit.” …Detached one- and two-family dwellings and townhouse units not more than three stories above grade plane in height with a separate means of egress and their accessory structures shall comply with the International Residential Code.

From the IRC proposal reason statement:

The IRC currently contains the terms “townhouse” and “townhouse unit,” but only “townhouse” is defined. Here are examples of a few of the locations where the term “townhouse unit” is currently used:

1. 1.Preamble “Effective Use of the International Residential Code,” which states: The International Residential Code (IRC) was created to serve as a complete, comprehensive code regulating the construction of single-family houses, two-family houses (duplexes) and buildings consisting of three or more townhouse units.”
2. 2.Section R302.2 states: Townhouses. Walls separating townhouse units shall be constructed in accordance with Section R302.2.1 or R302.2.2.
3. 3.Appendix K uses the term “townhouse units” throughout to describe individual dwelling units within a townhouse. The term “townhouse” is currently used interchangeably as referencing either a single dwelling unit or as a structure with three or more such units, even though the current definition does not accommodate the latter. Literally, the current definition of “townhouse” is a “townhouse unit,” yet previously approved code changes that introduced the term “townhouse unit” clearly demonstrate the confusion. I've also experienced this confusion when attempting to teach townhouse requirements to students in code classes.

This proposal will clarify the term “townhouse” as applying to structures that contain three or more dwelling units. This is consistent with how the IRC uses the term “dwelling” to reference a building with one or two dwelling units. Some of the text in the “dwelling” definition has been reproduced in the proposed “townhouse” definition, even though it's arguably poorly written. My objective was consistency, not fixing existing problems with the “dwelling” definition. It should be noted that, while the term “dwelling” currently captures buildings with up to two dwelling units, there is no term that currently defines a structure with more than two dwelling units. The updated definition of “townhouse” fills that hole.

To accommodate the need for a term that applies to individual dwelling units in a townhouse building, the proposal adds a new definition of “townhouse unit.” The new definition is correlated with and uses the term “dwelling unit.” For reference, the current IRC definitions of “dwelling” and “dwelling unit” are provided below, along with clean versions of the proposed “townhouse” and “townhouse unit” definitions for comparison:

1. 1.[RB] DWELLING. Any building that contains one or two dwelling units used, intended, or designed to be built, used, rented, leased, let or hired out to be occupied, or that are occupied for living purposes.
2. 2.[RB] DWELLING UNIT. A single unit providing complete independent living facilities for one or more persons, including permanent provisions for living, sleeping, eating, cooking and sanitation. For the definition applicable in Chapter 11, see Section N1101.6.
3. 3.[RB] TOWNHOUSE. A building that contains three or more attached townhouse units constructed in a group, and used, intended, or designed to be built, used, rented, leased, let or hired out to be occupied, or that are occupied for living purposes.
4. 4.[RB] TOWNHOUSE UNIT. A single-family dwelling unit in a townhouse that extends from foundation to roof and with a yard or public way on not less than two sides.