Exit Width and Travel Distance in a Converted Small Retail and Apartment Building
A two-storey building has a ground-floor retail store of 400 m² and a second-floor apartment of 120 m². The only interior stair is 900 mm wide and open to the retail store at the bottom. The retail store has a rear door 800 mm wide leading to a parking lot, and the front door is 900 mm wide. The apartment's occupant load is 6, and the store's calculated occupant load is 55. The building is unsprinklered. The owner wants to add a small mezzanine office of 40 m² above the store, accessed by a narrow ship ladder, without adding exits. The designer must assess whether the existing egress arrangement is adequate and whether the mezzanine can be added.
1. Assess the existing exit and stair arrangement for the retail store and apartment.
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The retail store has an occupant load of 55 and two exits at grade (front 900 mm and rear 800 mm), which is acceptable in principle because two exits are provided and their combined width is 1,700 mm, exceeding the required width at 5 mm per person (275 mm). However, the exits must be remote from each other, and the designer should verify that the front and rear doors are adequately separated. The apartment's single exit is the interior stair, which is open to the retail store at its base; this is a serious deficiency because the apartment's exit path passes through the store, and the stair is not separated from the store by a fire separation. The stair width of 900 mm is adequate for the small apartment load but the open connection means the apartment does not have a protected exit. The designer should recommend enclosing the stair with a fire separation and providing a self-closing door at the store level, or providing a separate exterior exit from the apartment.
2. Can the 40 m² mezzanine office be added using the ship ladder as its only access?
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The mezzanine office would add occupants and a new floor area within the store. A ship ladder is generally not acceptable as a means of egress for an occupied space; egress stairs must meet dimensional and tread requirements, and a ladder does not. The mezzanine would also need to be evaluated for occupant load and for whether it is considered a storey for area and height purposes. If the mezzanine is small enough to fall within mezzanine provisions, it may be permitted as an open mezzanine within the store, but it still requires a compliant stair and at least one exit that does not rely on a ladder. The designer should propose a proper stair, confirm the mezzanine's area does not push the building beyond permitted area, and verify that the mezzanine's occupants can reach the store's exits without passing through hazardous areas. Adding the office without a compliant stair would not be approvable.