Small Residential Addition: Part 9 Egress and Separation
A two-storey detached house (about 220 m2 per floor) is being renovated and enlarged. The owner adds a rear two-storey addition containing a new kitchen and family room on the ground floor and a master bedroom above. The existing single stair is 900 mm wide and serves both floors; it is open to the living room. The renovation adds a new bedroom in the basement and a secondary suite in the basement with its own kitchen. The designer proposes one exit from the basement suite through the existing stair, and one exterior door from the ground floor. Bedroom windows on the second floor are 600 mm wide by 800 mm high, with sills 1 100 mm above the floor. The building official questions egress from the basement suite and the bedroom window dimensions.
1. Evaluate the egress provisions for the basement suite and the second-floor bedrooms.
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Basement suite. A secondary suite in a basement requires a means of egress that does not depend solely on passing through the other suite. One exit through the existing stair, shared with the main dwelling, is generally not acceptable because the suite occupants would have to travel through the other unit and the stair is open to the living room. The suite needs its own exit or a compliant shared egress arrangement, and the stair should be separated from the suite and from the living area by a fire separation with a self-closing door.
Bedroom windows. Unprotected openings for escape from bedrooms must meet minimum dimensions: typically an unobstructed opening of at least 0.35 m2 with no dimension less than 380 mm, and a sill height not more than 1 000 mm above the floor (or a step is provided). The proposed 600 mm x 800 mm window gives 0.48 m2, which is adequate in area, but the 1 100 mm sill exceeds the maximum unless a step or platform is provided. The opening must also be operable from the inside without keys or tools.
Stair width. 900 mm is marginal; the stair serving both floors must be adequate for the occupant load and should be checked against the Part 9 minimum width.
2. The owner argues that because the house is small and Part 9 applies, the basement suite does not need a separate exit. How should this be assessed?
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Part 9 does not eliminate the requirement for a safe means of egress from a secondary suite. The suite is a separate dwelling unit and its occupants must be able to escape without passing through another suite. A single shared stair open to the living room does not provide that independence and exposes suite occupants to smoke from the main dwelling.
The correct approach is to provide the suite with its own exit or a compliant shared egress path, and to separate the suite from the rest of the dwelling by a fire separation with a self-closing door. The stair should be enclosed or otherwise protected. If a separate exterior exit is impractical, an alternative solution may be considered, but it must demonstrate equivalent life safety - for example, a rated separation, interconnected smoke alarms, and a protected path - not merely the small size of the house.