Proposed Change 1784

Farm buildings are unique in their occupancy, uses, hazards and expected performance. The National Building Code of Canada (NBC) 2020 reflects this by including suitable minimum requirements for farm buildings and agricultural occupancies in Part 2 of Division B.

Currently, openable windows or panels that are used as exits in farm buildings have no requirements for interior sill height. To ensure that the exit can be used in an emergency, a maximum sill height should be specified so that any farm building occupant can quickly evacuate through these openable windows. Window sills that are too high could expose the occupant to an unacceptable risk of being trapped in case of a fire emergency.

Parts 3 and 9 specify a maximum interior sill height of 900 mm for exits to fire escapes through windows in dwelling units. This proposed change uses the same height for the majority of locations within a farm building.

In areas where openable windows or panels are used as exits in areas of farm buildings that are occupied by livestock, low sill heights could allow access to the opening by the livestock, which could also disrupt ventilation systems, allow the livestock to escape, or defeat biosecurity measures within barns.

A minimum sill height of 1.5 m would be high enough to limit any interference from livestock, while still being a manageable height for occupant egress in an emergency. This height was chosen based on practical use and following the recommendations in explanatory Note A-9.9.10.1.(1) on escape windows from bedrooms in dwelling units.

This proposed change is anticipated to have minimal cost implications as the foothold could have various forms and installations (e.g., a piece of wood attached to the wall, an appropriate sized hole in a concrete wall).

This proposed change provides enforceable, safe and practical requirements for the sill height of windows or panels used as exits in farm buildings, which is not currently specified in the NBC. It would also facilitate the quick evacuation of farm building occupants in case of an emergency.

This proposed change can be enforced using the existing regulatory framework. Authorities having jurisdiction would already be familiar with these requirements, as they have been in force for Part 3 and Part 9 buildings for some time. The application to Part 2 farm buildings would be similar, with a clear relaxation for livestock-occupied parts of farm buildings.

Those concerned with the design, construction and operation of farm buildings, namely, engineers, architects, building owners and regulators would be affected by this proposed change.

Building owners, in conjunction with designers, would be provided with clear requirements allowing them to design and construct farm buildings that meet their specific requirements.