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Prototype 4

6 storeys / 18 units / 40’ lot



Typology
Six-Storey Apartment Building
Occupancy
Group C - 18 Dwelling Units
Classification
NBC 3.2.2.51


This scenario proposes a six-storey apartment building on an average 40’ (20.2m) lot width along a mixed-use street. This is a common dimension for properties along main streets in urban areas across Canada. The proposed single exit stair (SES) building design contains one 3-bedroom, two 2-bedroom and one 1-bedroom unit on each of the upper floors (total of 18 homes) with a garbage, bicycle, storage and mechanical room on the ground floor. A separate 40m2 small-scale retail or office space (commercial unit) is also shown on the ground floor of the building. The uppermost storey includes a common amenity space that could be deleted to add two more homes.

The typical floor plan of the upper storeys has 8 bedrooms such that the SES serves a total of 16 occupants per storey (calculated as 2 persons per bedroom), which is 26.7% of the 60 person occupant load permitted for floor areas served by a single exit in the National Building Code of Canada. The cumulative occupant load served by the SES on all upper storeys therefore equals 72 persons. The design provides a direct exit discharge to the exterior on the ground floor and another path of travel through the residential lobby to the street, located within close proximity of the fire access route.



Lot Size
40’ x 120’

Lot Area
446.5m2
(4,800 sq.ft.)

Lot Coverage
65.4%

Building Area
292.0m2

Building Height
6 storeys

Building Depth
 26.0m

Gross Floor Area
1,670.1m2

Floor Space Index
3.74
Residential Unit Mix
18 dwelling units
(8x2-Bed, 5x3-Bed, 5x1-Bed)

Occupant Load (SES)
72 persons

Occupant Load (per storey)
16 persons

Exit Facility Width
1100mm



Floor Area Efficiency

single stair = 87.8%
scissor stair = 83.8%

+4.0%


Construction Cost (Direct Only)

single stair = $6,103,000 ($332/sf)
scissor stair = $6,186,800 ($323/sf)

-1.4% (-$83,800)



Net Operating Income (Rental)

single stair = $428,830 annualized
scissor stair = $419,360 annualized

+2.3% (+$9,470)



The floor plans below compare the SES building design with an overlay of the prescriptive requirement for two exit stairs. As a measure of leasable floor area, a single stair increases the efficiency of the typical floor plan by 4.0%. The two-stair design increases the gross construction area of the building to eliminate one of the lightwells. This removes the opportunity for daylight in the public corridor and reduces one of the bedrooms on each upper floor to a windowless den. The construction costing of the building (with no change in overall building size and accounting for the cost of additional fire and life safety measures) shows a difference attributed to the additional exit stair compared to the cost of additional windows and building envelope. The impact of changing one of the bedrooms to a den on each storey is also captured in terms of rental income.










Appendix (Downloads)

SES Prototype 4 - Class D Construction Costing (2025.02.12)

SES Prototype 4 - Pro Forma Analysis (2025.03.10)



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