Typology
6-Storey Mixed-Use Building

Occupancy
Group C, 20 Dwelling Units

Classification
2024 Manitoba Building Code, Part 3

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Status: Submitted for Building Permit, City of Winnipeg (March 2025)

This narrow 31 ft wide by 108 ft long (9.5m x 33m) property is surrounded by underutilized surface parking lots in downtown Winnipeg. The proposed six storey building optimizes the use of the property as a mixed-use development with 4 dwelling units on each floor for a total of 20 residential units on the upper storeys of the building. The ground floor and mezzanine level also contains an office space and a flexible space for a small-scale commercial use such as a coffee shop, storefront or an exhibition space.The street facing elevations are fully glazed and the long facades along the property line are sculpted to express the structural system.

A key aspect to making this project feasible is the efficiency of the single stair design to maximize usable and habitable floor area. The proposed design also features exterior passageways in lieu of interior corridors as a passive smoke protection measure.

As illustrated in the diagram below, ‘scissor exit stairs’ is a prescriptive solution to provide two means of egress and results in a 20% loss in gross rentable floor area; the standard ‘two exit stairs’ solution is slightly more efficient for this particular project and results in a loss of 18% in gross rentable floor area. A ‘single exit stair’ (SES) building design results in the most efficient floor plate and minimizes the reduction in gross rentable floor area to 13%.

Multi-unit residential buildings typically require a floor area efficiency of at least 85% to be financially viable, such that these incremental differences have a significant impact on project viability, making single exit stair (SES) designs a worthwhile strategy for small footprint developments.

Housing Supply Impact
The reduction of net floor space reduces the size of suites and their ‘effectiveness’ in providing housing. The ‘scissor exit stairs’ scenario results in 5 studio (5 occupants) and 15 one-bedroom suites (30 occupants) for an effective housing supply of 35 occupants (5+30). The standard two exit stairs solution results in 5 studio, 10 one-bedroom and 5 two-bedroom suites for an effective housing supply of 45 occupants (5+20+20). Comparatively, the single exit stair solution results in 10 one-bedroom suites and 10 two-bedroom suites for an effective housing supply of 60 occupants (20+40) as the area consumed by circulation is unlocked as habitable floor area on each upper storey of the building.

Construction Cost Impact
Exit stairs are some of the most costly elements to construct alongside kitchens, bathrooms, elevators, and mechanical systems in apartment buildings. As the number of dwelling units does not vary across the three scenarios depicted above, the number of kitchens, bathrooms, elevators, and mechanical systems is constant. However, eliminating the second exit stair has a significant effect on construction cost. We estimate that the projected cost of the proposed building is in the range of $3,200/m² ($297 per sq.ft.) and the pro-rated stair construction is in the range of $5,000/m². Savings in construction cost per square meter is estimated by returning the area consumed by the scissor stair to habitable floor area:

$5,000 x 18m² per storey = $90,000 x 6 storeys = ± $540,000
$3,200 x 18m² per storey = $57,500 x 6 storeys = ± $345,000
Capital Cost Saving = ± $205,000

This represents a 2.5% savings on the overall construction budget of ± $7,900,000.

Development Revenue Impact
However the revenue gain per floor is more significant as a measure of long-term feasibility than upfront construction cost. The single stair scenario brings revenues up by 3 bedrooms per floor compared to the scissor stair scenario. At current rental rates in Winnipeg, this is about $450 for every additional bedroom (studio rents: $850/month, one-bedroom rents: $1,300/month, two-bedroom rents: $1,750/month). Across 5 upper storeys, this results in an estimated monthly revenue increase of $6,750 or an annual increase of $81,000 in additional revenue. Based on a potential gross annual revenue of approximately $285,000 for the scissor stair configuration, this results in a potential gross revenue increase of 28%.

Proposed Solution: Provision of Single Exit at Levels 2 to 6

Code Reference: Sentence 3.4.2.1.(1)

Intent: The intent in providing at least two exits from a floor area is twofold:

To limit the probability that persons will not have a choice of an alternative exit in the event that one exit is blocked or obstructed in an emergency situation, which could lead to delays in the evacuation or movement of persons to a safe place, which could lead to harm to persons, and
 
To limit the probability that emergency responders will not have a choice of an alternative exit in the event that one exit is blocked or obstructed in an emergency situation, which could lead to emergency responders being delayed in gaining access to a floor area, which could lead to delays or ineffectiveness in emergency response operations, which could lead to delays in the evacuation or movement of persons to a safe place, which could lead to harm to persons, or damage to the building.

Alternative Solution: Level of performance will be analyzed on the basis of a comparative analysis to the acceptable solution. Proposed mitigating measures and building design features will be evaluated to demonstrate an acceptable level of performance.

Proposed features include:

• Mechanically pressurized exit stair
  
• Mechanically pressurized elevator lobby, which acts as an area of refuge
  
• 45 minute fire-protection rating of dwelling unit entry doors
  
• Sprinklering throughout, including at all exit stair landings 
  
• Increased stair width for counterflow of occupants and firefighters
  
• Cumulative exiting
  
• Increased compartmentation of public corridor
  
• Travel distance from most remote point at Level 6 to point in exit stair where choice of egress (at Level 2) is provided is less than maximum Division B travel distance to exit on a single floor area 
  

Inherent features include:

• Small building area
• Low occupant load, maximum 12 persons per storey
• Maximum of 60 persons served by exit stair
• Short travel distance to point in which one has choice in egress direction
• Public corridors open to exterior, naturally ventilated
• NLT floor assemblies eliminate risk associated with concealed spaces
• Fire Department access to two building faces

Analysis exercises

• Egress analysis
• Probability-failure risk analysis based on probable/possible fire scenarios
• Comparison to Seattle Building Code SES provisions
• Comparison to BCBC 2024 code change for SES

The building employs a heavy timber structure for the columns, beams and floors to reduce its carbon footprint. From a structural design perspective, typical moment frames characterized by 90º connections between columns and beams require additional diagonal bracing at the narrow ends. Instead, the proposed lateral support structure consists of diagonal columns to eliminate the need for additional cross-bracing. These columns are located on the southwest and northeast ends of the building and are directly expressed in the building form. The heavy timber column and beam system is further assisted by the rigidity of the central stair and elevator core.