Toronto (work in progress, illustrations coming soon)
As part of the Expanding Housing Options in Neighbourhoods (EHON) initiative, the City of Toronto is considering planning reforms to allow as-of-right permissions for small apartment buildings of up to six storeys and 30 units along Major Streets. The proposed zoning by-law amendment provides
built-form performance standards such as maximum building height, maximum building depth and minimum setbacks.
Much like the 2010 Midrise Performance Standards, the proposed built-form constraints do not specifically address the question of lot width beyond conditions for side yard setbacks. There are several examples of wider corner lots and assembled mid-block conditions that have been assembled and re-developed as midrise buildings. However narrow lots do not afford the same economies of scale and the building code requirement for two exit stairs severely limits the feasibility of such sites.
Much like the 2010 Midrise Performance Standards, the proposed built-form constraints do not specifically address the question of lot width beyond conditions for side yard setbacks. There are several examples of wider corner lots and assembled mid-block conditions that have been assembled and re-developed as midrise buildings. However narrow lots do not afford the same economies of scale and the building code requirement for two exit stairs severely limits the feasibility of such sites.
DIAGRAM HERE SHOWING PROPOSED BY-LAW
6 storeys, 25m building depth, 30m+ lot width, side setbacks 1.8m
Adjacent buildings shown as houses
6 storeys, 25m building depth, 30m+ lot width, side setbacks 1.8m
Adjacent buildings shown as houses
“The zoning by-law amendment proposes apartment buildings abutting lots on major streets will generally have a maximum permitted building length and depth of 25 metres and 27 metres, respectively. These permissions will accommodate the arrangement of a double-loaded corridor and are supported by modeling that incorporates the other proposed built-form standards, particularly minimum front and rear yard setbacks, to ensure adequate open space and separation distances are maintained.”
- City of Toronto, Major Streets Study - Proposals Report (September 14, 2023).
The proposed zoning by-law amendment can be used to test the feasibility of small apartment buildings depending on the available street frontage. Below are a series of typical floor plans comparing exit stair design in relation to lot width. In order for a housing project to be financially feasible, the floor area efficiency, measured as a ratio of residential area (area of the units) to gross construction area (area of the building) should exceed 85-90 percent.
As sites become smaller, the requirement for two stairs becomes more difficult to accomodate. While scissor stairs are more efficient than two entirely independent stairs, the requirement for a minimum separation distance between access to exits remains challenging to accomodate. Single stair designs maximize floor area efficiency and provide design flexibility for more diverse unit layouts.
“Typical Plan is an American invention. It is zero-degree architecture, architecture stripped of all traces of uniqueness and specificity. It belongs to the New World.”
- Rem Koolhaas. (1993). S,M,L,XL.
Two Stairs - Typical Floor Plan Comparison (Lot Width Increments of 5m)
1. FLOOR PLAN COMPARISON - DOUBLE LOADED CORRIDOR on a 40m frontage
2. FLOOR PLAN COMPARISON - DOUBLE LOADED CORRIDOR on a 35m frontage
3. FLOOR PLAN COMPARISON - DOUBLE LOADED CORRIDOR on a 30m frontage
Scissor Stairs
- Typical Floor Plan Comparison
(Lot Width Increments of 3m)
4. FLOOR PLAN COMPARISON - SCISSOR STAIR on a 30m frontage
5. FLOOR PLAN COMPARISON - SCISSOR STAIR on a 27m frontage
6. FLOOR PLAN COMPARISON - SCISSOR STAIR on a 24m frontage
7. FLOOR PLAN COMPARISON - SCISSOR STAIR on a 21m frontage
8. FLOOR PLAN COMPARISON - SCISSOR STAIR on a 18m frontage
9. FLOOR PLAN COMPARISON - SCISSOR STAIR on a 15m frontage
10. FLOOR PLAN COMPARISON - SCISSOR STAIR on a 12m frontage
11. FLOOR PLAN COMPARISON - SCISSOR STAIR on a 9m frontage
12. FLOOR PLAN COMPARISON - SCISSOR STAIR on a 6m frontage
Rules of Thumb:
- 25.0m building depth
- mid-block lot condition with minimum 1.8m side yard setbacks.
- structural grid at 3.0m span o/c (bedrooms at least 9’0 wide)
- 3.0m floor to floor heights equals 17 treads (maximum rise: 180mm / minimum run: 280mm)
- 1100mm minimum width of public corridors per OBC 3.4.3.2. and 3.3.1.9.
- 1800mm accessible turning radius every 30m in public corridors per 3.8.1.3.
- generic wall types and thicknesses based on OBC Vol. 2, MMAH Supplementary Standard SB-3
- 9.0m minimum distance between exits per OBC 3.4.2.3.
- 6.0m maximum dead-end corridor travel distance per OBC 3.3.1.9. (9)
- assume garbage room on ground floor sufficient <30 units (i.e. no garbage chute) per Toronto ZBL Chapter 220
- provide one full-size elevator (interior cab dimension per OBC 3.5.4.1 - 2032mm x 1295mm)
Further Reading
City of Toronto. “Major Streets Study.” Expanding Housing Options in Neighbourhoods.
https://www.toronto.ca/city-government/planning-development/planning-studies-initiatives/major-streets-study/
City of Toronto Zoning By-Law 569-2013.
https://www.toronto.ca/city-government/planning-development/zoning-by-law-preliminary-zoning-reviews/zoning-by-law-569-2013-2/
2012 Ontario Building Code, Division B - Part 3.
https://www.ontario.ca/laws/regulation/120332
Rotsztain, Daniel. (2019). “The Mid-rises of Metropolitan Toronto” in House Divided: How the Missing Middle Will Solve Toronto's Housing Crisis.