Prototype 5
3 storeys / 8 units / 50’ lot
Typology
Three-Storey Apartment Building
Three-Storey Apartment Building
Occupancy
Group C - 8 Dwelling Units
Group C - 8 Dwelling Units
Classification
NBC Part 9
NBC Part 9
This scenario proposes a three-storey small apartment building on a typical 50’ (15.2m) wide residential lot. This lot dimension is common in residential neighbourhoods across Canada, particularly for larger lots in post-war suburbs developed after World War 2.
The proposed single exit stair (SES) building design contains three residential units on each of the upper floor levels and two units on the ground floor (total of 8 homes), as well as the common garbage, bicycle, storage and mechanical room on the ground floor. The single exit stair serves a total of 24 occupants (calculated as 2 persons per bedroom), which is less than half of the 60 person occupant load permitted for floor areas served by a single exit in the National Building Code of Canada. Given this low occupant load, a minimum exit facility width of 1100mm is provided, increased from the minimum prescriptive width of 900mm permitted for Part 9 buildings. The design provides a direct exit discharge on the ground floor located within proximity of the fire access route.
Lot Size
50’ x 100’
Lot Area
464.5m2
(5,000 sq.ft.)
Lot Coverage
50%
Building Area
232.5m2
Building Height
3 storeys
Building Depth
19.0m
Gross Floor Area
697.8m2
Floor Space Index
1.50
Residential Unit Mix
8 dwelling units
(3x1-Bed, 3x2-Bed, 2x3-Bed)
Occupant Load (SES)
24 persons
Occupant Load (per storey)
12 persons
Exit Facility Width
1100mm
50’ x 100’
Lot Area
464.5m2
(5,000 sq.ft.)
Lot Coverage
50%
Building Area
232.5m2
Building Height
3 storeys
Building Depth
19.0m
Gross Floor Area
697.8m2
Floor Space Index
1.50
Residential Unit Mix
8 dwelling units
(3x1-Bed, 3x2-Bed, 2x3-Bed)
Occupant Load (SES)
24 persons
Occupant Load (per storey)
12 persons
Exit Facility Width
1100mm
Floor Area Efficiency
single stair = 88.2%
scissor stair = 81.9%
+6.3%
Construction Cost (Direct Only)
single stair = $2,493,400 ($328/sf)
scissor stair = $2,491,300 ($327/sf)
+0.1% (+$2,100)
Net Operating Income (Rental)
single stair = $177,470 annualized
scissor stair = $170,230 annualized
+4.3% (+$7,240)
The floor plans below compare the single stair building design with an overlay of the prescriptive requirement for two exit stairs. As a measure of leasable floor area, the single stair increases the efficiency of the typical floor plan by 6.3%. The scissor stair plan reduces the size of the 1-bedroom dwelling unit to a studio that does not meet accessible design standards. Alternatively, the elevator could be deleted as it is not required for Part 9 buildings. 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 staircase, partitions and doors, compared to the cost of the sprinkler system. The impact of changing the three accessible 1-bedroom units to smaller studio units is also captured in terms of rental income.
Appendix (Downloads)
SES Prototype 5 - Class D Construction Costing (2025.02.12)
SES Prototype 5 - Pro Forma Analysis (2025.03.10)
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