The Seattle Building Code permits apartment buildings of up to six storeys to be served by a single exit stair.

This is one of the only jurisdictions in the United States to permit single exit apartment buildings at such height and many such projects have been realized in recent years, especially as zoning regulations are revised to accomodate increased density near new public transit infrastructure. Seattle Building Official Ardel Jala confirmed that this is not a recent change and dates back to the 1977 Seattle Building Code, commenting that “The driver for these code changes was the development happening at the time being constrained by building code requirements. There were many small lots being developed and two exits took up a significant portion of the floor plate.” It is also remarkable that Seattle is less restrictive than the rest of North America despite being a high-risk seismic zone along the Pacific Ocean Ring of Fire.

While the model code that most American cities is based on, the International Building Code (IBC), permits up to four storeys to be served by a single stair, the Seattle Building Code is distinct in allowing for up to six storeys. The 2018 Seattle Building Code, Chapter 10: Means of Egress, Subsection 1006.3.3 Single Exits outlines the requirements for such buildings. A read-only version of the document is accessible here.

1006.3.3 Single Exits

7. Not more than 5 stories of Group R-2 occupancy are permitted to be served by a single exit under the following conditions:

7.1. The building has not more than six stories above grade plane.

7.2. The building does not contain a boarding house.

7.3. There shall be no more than four dwelling units on any floor.

7.4. The building shall be of not less than one hour fire-resistive construction and shall also be equipped throughout with an automatic sprinkler system in accordance with subsection 903.3.1.1. Residential-type sprinklers shall be used in all habitable spaces in each dwelling unit.

7.5. There shall be no more than two single exit stairway conditions on the same property.

7.6. An exterior stairway or interior exit stairway shall be provided. The interior exit stairway, including any related exit passageway, shall be pressurized in accordance with subsection 909.20. Doors in the stairway shall swing into the interior exit stairway regardless of the occupant load served, provided that doors from the interior exit stairway to the building exterior are permitted to swing in the direction of exit travel.

7.7. A corridor shall separate each dwelling unit entry/exit door from the door to an interior exit stairway, including any related exit passageway, on each floor. Dwelling unit doors shall not open directly into an interior exit stairway. Dwelling unit doors are permitted to open directly into an exterior stairway,

7.8. There shall be no more than 20 feet (6096 mm) of travel to the exit stairway from the entry/exit door of any dwelling unit.

7.9. Travel distance measured in accordance with section 1017 shall not exceed 125 feet (38100 mm).

7.10. The exit shall not terminate in an egress court where the court depth exceeds the court width unless it is possible to exit in either direction to the public way.

7.11. Elevators shall be pressurized in accordance with section 909.21 or shall open into elevator lobbies that comply with section 713.14. Where approved by the building official, natural ventilation is permitted to be substituted for pressurization where the ventilation would prevent the accumulation of smoke or toxic gases.

7.12. Other occupancies are permitted in the same building provided they comply with all the requirements of this code. Other occupancies shall not communicate with the Group R occupancy portion of the building or with the single-exit stairway. Exception: parking garages and occupied roofs accessory to the Group R occupancy are permitted to communicate with the exit stairway.

7.13. The exit serving the Group R occupancy shall not discharge through any other occupancy, including an accessory parking garage.

7.14. There shall be no openings within 10 feet (3048 mm) of unprotected openings into the stairway other than required exit doors having a one-hour fire-resistance rating.

Capitol Hill Urban Cohousing

Schemata Workshop (2016)
1720 12th Ave, Seattle, WA 98122, USA

Height: 5 storeys (58 ft / 17m)
Use: 9 dwelling units, 1 commercial at grade
Floor Area: 17,600 ft²  / 1,635 m²
Construction: Type V-A (upper floors) and Type I-A (ground) 
Stair: Galvanized Steel
Sprinklered: Yes (required throughout)


This is an example of what can be built using the single exits provision in the Seattle Building Code. A five storey co-housing project on a small ‘main streets’ infill site measuring 40ft by 113ft (4520ft² or 420m²). The architect claims that requiring a second stair would have decreased the design from nine to six dwelling units, and likely made the project financially unviable as affordable housing. The arrangement of the exterior passageway/balcony on each level in relation to the courtyard also promotes casual interaction between residents. The architects explored mass timber as construction type, but for cost-reduction purposes executed the project in four storeys of Type V-A protected wood frame above a podium of Type I-A non-combustible reinforced concrete. The architects would have liked to have been able to build to the maximum height limit for single exits at 6 storeys, but were limited by the zoning by-law to a maximum building height of five storeys.

Read the interview with architect Mike Mariano

301 Belmont

Workshop AD (under construction, 2022)
301 Belmont Ave E, Seattle, WA 98102, USA

Height: 7 storeys (74 ft / 22.5m)
Use: 29 dwelling units
Floor Area: 19,900 ft²  / 1,850 m²
Construction: Type III-A (upper floors) and Type I-A (ground)
Stair: Reinforced Concrete
Sprinklered: Yes (required throughout)


This is an apartment building currently under development in Seattle pursuing alternative methods compliance to the single exits provision of the Seattle Building Code. It is included to demonstrate the flexibility of the code and authorities having jurisdiction, which approved the architect’s application to exceed the single exits building height restriction of six storeys to match the zoning limit of seven storeys. The exiting stragety divides the building into two sections such that a single stair serves the upper storeys (floors three to seven), functions as blind shaft on the second floor and then discharges to the exterior at grade. A separate exit stair serves the basement, ground floor and second floor, exiting through the lobby to the exterior. The approved building code modification request is included below.

Ardel Jala, Building Official
Seattle Department of Construction and Inspections

Proposed Building Code Modification for 301 Belmont Ave. E. Project No. 6686874-CN


Dear Ms. Jala,

The architect on this project is Steve Bull with workshop A.D. and the code consultant is William Justen. We are proposing this Building Code Modification per: 104.4 Modifications, The building official may modify the requirements of this code for individual cases provided the building official finds: (1). There are practical difficulties involved in carrying out the provisions of this code: (2) the modification is in conformity with the intent and purpose of this code; and (3) the modification will provide a reasonable level of strength, effectiveness, fire resistance, durability, safety and sanitation when considered together with other safety features of the building, or other relevant circumstances. The building official may, but is not required to, record the approval of modifications and any relevant information in the files of the building official or on the approved construction documents.

We are proposing a modification for this project to SBC 1006.3.2 Single exits

7. Not more than 5 stories of Group R-2 occupancy are permitted to be served by single exit under the following conditions:

7.1 The building has not more than six stories above grade plane

7.2 through 7.14 code requirements will all be satisfied completely

For this individual case we are requesting a modification to 7.1 allowing our building to be seven stories above gradeplane. Our rationale for this modification includes the following responses to the findings necessary by the building official to accept our proposed modification:

1. “There are practical difficulties involved in carrying out the provisions of this code:”

a. This platted site is unusually small with a land area of only 3,952 square feet.

b. With the required land use and building code setbacks, the gross floor area of levels 2 and 3 are only 2,513 square feet.

c. With required clearances for SCL powerline clearances on Belmont, the gross floor areas for levels 4, 5, 6 and 7 are further reduced to 2,260 square feet.

d. With two stair enclosures, a corridor and an elevator, the habitable floor area would be reduced on those upper floors to approximately 1,900 square feet each.

e. The current plans being reviewed by SDCI with two stair enclosures show five apartments per story with the units averaging 383 square feet for a total of 35 units.

f. If the modification is approved, we would reduce the number of units to four per story to meet section 1006.3.2.7.3 and the units would average a more desirable 482 square feet for a total of 29 units. The practical occupant load will likely be lower with the 4 units rather than 5 units per story.

2. “The modification is in conformity with the intent and purpose of this code:”

a. The other 13 conditions described in 7.2 through 7.14 will all be satisfied

b. The requirement described in the introductory paragraph 7.: “Not more than five stories of group R-2 occupancy are permitted to be served by a single exit under the following conditions:”. This will be complied with by our design, which would have a single stair serving only five stories, levels 3 through 7, and below level 3 that single stair would be a blind shaft not accessible to levels 1 and 2 below, but that stair will exit directly to a yard leading to a public way. A separate, independent exit stair would serve levels 1 and 2 and exit through the lobby directly to the public way.

3. “The modification will provide a reasonable level of strength, effectiveness, fire resistance, durability, safety and sanitation when considered together with other safety features of the building, or other relevant circumstances.”

a. The upper six stories will be Type III-A (protected combustible) construction over a Type I-A (fire-resistive non-combustible) first story and basement which is actually less than the code would allow of six stories of Type III-A over a full two stories of Type I-A.

b. By using the single stair serving the rooftop amenity, the occupant load would be limited to 10 persons with the maximum occupied amenity area of 150 square feet. The current plans using the two exit stairs serving the roof has assumed an occupant load of 43 persons with the occupied roof amenity area of 643 square feet. Clearly the lower occupant load on the roof reduces risk of life safety.