Read in conjunction with "CNL Business Hub Building Application of the National Building Code"
Morrison Hershfield Limited (MH) has been retained by HDR Architects to investigate the application of the 2015 National Building Code (NBC) and prepare this Alternative Solution to rationale the proposed combustible construction of the Canadian Nuclear Laboratories (CNL) Business Hub Building, in Chalk River, Ontario. The building is proposed to be constructed of combustible materials in accordance with the requirements for mid-rise wood construction provisions of the NBC for buildings up to 6 storeys in building height per the National Building Code of Canada (NBC) Division B, Article 18.104.22.168. and associated provisions.
Per the prescriptive provision of the Clause 22.214.171.124.(1)(c), a building is permitted to be constructed of combustible construction if it has a height of not more than 18 m measured between the floor of the first storey and the uppermost floor level. The proposed building will be 21.6 m in building height based on the elevation and by virtue of the location of grade at Level 1 per the NBC.
In addition, Clause 126.96.36.199.(2)(c) requires that where the height of the roof assembly is more than 25 m measured from the floor of the first storey to the highest point of the roof, that portion of the roof is to be constructed of noncombustible construction or fire-retardant treated wood conforming to Article 188.8.131.52. The roof height is 25.6 m and is proposed to be of combustible construction.
It is noted that although there are restrictions on the location of Group A, Division 2 major occupancies within a building conforming to Article 184.108.40.206., in this case, the Group A, Division 2 occupancy is considered to be subsidiary to the Group D major occupancy. To address the performance required by Article 220.127.116.11, this Alternative Solution proposes that the following features be incorporated into the design:
(1) The first storey (Level 1) is to be constructed of noncombustible construction including Level 1 and 2 floor slabs and supporting construction.
(2) The sprinkler density otherwise required by NFPA 13 is to be increased by one hazard classification throughout the building.
(3) The Fire Department access route required by the NBC will be provided to the main entrance at Level 2 at the west end of the building and ensuring that the access route is within 3 to 15 metres of not less than 25% of the building perimeter and located such that it is not more than 20 metres between the level of the access route and the floor of the top storey.
This report presents the analysis of the performance of the proposed mitigating and compensating measures to support the application of Article 18.104.22.168. The description of the Alternative Solution is in Section 3.6 of this report.