Prototype 6
3 storeys / 5 units / 30’ lot
Typology
Three-Storey Apartment Building
Three-Storey Apartment Building
Occupancy
Group C - 5 Dwelling Units
Group C - 5 Dwelling Units
Classification
NBC Part 9
NBC Part 9
This scenario proposes a three-storey small apartment building on a 30’ (9.1m) wide corner lot. This is a typical lot dimension in residential neighbourhoods across Canada. The proposed single exit stair (SES) building design contains two homes on each of the upper floor levels and one home on the ground floor (total of 5 dwelling units), as well as the common garbage and mechanical room on the ground floor. The ground floor also contains a separate commercial unit (non-residential use) such as a corner store or coffee shop.
The single exit stair serves a total of 12 occupants (calculated as 2 persons per bedroom), which is 20% of the 60 person occupant load permitted for floor areas served by a single exit in the National Building Code of Canada. Given this very 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 is proposed as an exterior staircase protected from snow and rain accumulation and provides a direct exit discharge on the ground floor located within proximity of the fire access route.
Lot Size
30’ x 100’
Lot Area
278.7m2
(3,000 sq.ft.)
Lot Coverage
50%
Building Area
139.7m2
Building Height
3 storeys
Building Depth
19.0m
Gross Floor Area
419.1m2
Floor Space Index
1.50
Residential Unit Mix
5 dwelling units
(3x1-Bed, 2x2-Bed)
Occupant Load (SES)
12 persons
Occupant Load (per storey)
6 persons
Exit Facility Width
1100mm
30’ x 100’
Lot Area
278.7m2
(3,000 sq.ft.)
Lot Coverage
50%
Building Area
139.7m2
Building Height
3 storeys
Building Depth
19.0m
Gross Floor Area
419.1m2
Floor Space Index
1.50
Residential Unit Mix
5 dwelling units
(3x1-Bed, 2x2-Bed)
Occupant Load (SES)
12 persons
Occupant Load (per storey)
6 persons
Exit Facility Width
1100mm
Floor Area Efficiency
single stair = 100.0% (91.0%)*
scissor stair = 88.3%
Δ 11.7%
* 2.7% if including exterior stair
Construction Cost (Direct Only)
single stair= $1,901,300 ($464/sf)
scissor stair = $1,888,400 ($403/sf)
+0.7% (+$12,900)
Net Operating Income (Rental)
single stair = $132,570 annualized
scissor stair = $122,980 annualized
+7.8% (+$9,590)
*
size of
retail unit
reduced by 32% (rents per sq.ft.)
The floor plans below compare the sinlge stair building design with an overlay of the prescriptive requirement for two exit stairs. As a measure of leasable floor area, a scissor-stair plan reduces the efficiency of the typical floor plan by 11.7% (measured to exterior walls and excluding the exterior staircase) and reduces the size of the ground floor commercial unit by 14.5m2. The construction costing of the building (including the change in gross construction area due to the fire separation of the scissor stair and the cost of additional fire and life safety measures) shows a difference attributed to the cost of the fire sprinkler system. The impact of reducing the floor area of the commercial unit is also captured in terms of rental income.
Appendix (Downloads)
SES Prototype 6 - Class D Construction Costing (2025.02.12)
SES Prototype 6 - Pro Forma Analysis (2025.03.10)
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