Related sections in the International Building Code (IBC) were reviewed regarding use of wood components in non-combustible buildings, and light-frame wood buildings or heavy timber buildings greater than 4-storeys in height.
The highlights of this review are:
a) Fire-retardant-treated (FRT) wood can be used in partitions when the required fire-resistance rating is not more than 2 hours. This includes all types and occupancy groups of Types I and II construction;
b) FRT wood can be used in non-bearing exterior walls in Type I, II, III and IV construction;
c) Wood components can be used in interior walls for Type III and IV construction;
d) Wood components can be used in both interior and exterior walls for Type V construction.
When a sprinkler system is installed according to NFPA 13 , it is possible to build a light-frame wood building or heavy timber building over 4-storeys according to the following provisions:
a) Type IIIA 6-storey light-frame wood buildings using FRT wood for exterior walls for Occupancy group B (Business), H-4, and 5-storey light-frame wood buildings for Occupancy group F-2, H-3, I-1(Institutional), R (Residential), S-2;
b) Type IIIB 5-storey light-frame wood buildings using FRT wood for exterior walls for Occupancy group R;
c) Type IV (HT) 6-storeys timber buildings for Occupancy group B, F-2, H-4 and S-2;
d) Type IV (HT) 5-storeys timber buildings for Occupancy group F-1, H-3, I-1, R, S-1 and U.
This project evaluates the National Building Codes of Canada (NBCC) clauses relevant to fire performance and performance requirements of non-load-bearing wood-frame in-fill walls in concrete/steel hybrid buildings. Related clauses in NBCC are reviewed regarding the use of wood components and non-load bearing wall systems in non-combustible buildings. The highlights of this review are:
§ An exterior non-loadbearing wall assembly with combustible components is allowed in non-combustible construction if:
a) Building height is not more than 3 storeys or has a sprinkler system throughout ;
b) The interior surfaces of the wall assembly are protected by a thermal barrier ; and
c) The wall assembly satisfied the testing criteria for CAN/ULC S134 ;
§ Combustible interior wall finishes, other than foamed plastics, are allowed in non-combustible construction if the thickness is not greater than 25 mm and their flame spread rating (FSR) is not more than 150 ;
§ Combustible insulation, other than foamed plastics, is allowed in non-combustible construction if the flame-spread rating not more than 25 ;
§ Combustible insulation with a FSR not less than 25 and not more than 500 is allowed in exterior and interior walls of non-combustible construction if the building is non-sprinklered and not more than 18 m or sprinklered and protected by a thermal barrier ;
§ There are no obstacles for using wood-frame in-fill wall systems for interior partition walls in hybrid buildings:
a) For non-sprinklered buildings not greater than 3 storeys or a floor area not greater than 600 m2 ;
b) For sprinklered buildings.
§ Non-combustible construction allows combustible elements in partition walls in the following instances:
a) Solid lumber partitions located in a fire compartment area are permitted in a non-sprinklered floor area not greater than 600 m2 with restrictions ;
b) Solid lumber partitions not less than 38 mm thick and partitions that contain wood framing are permitted with restrictions.
§ Combustible cladding can be used under the following circumstances:
a) When a wall assembly with exposing building face is between 10 to 25% tested by CAN/ULC-S134 and complies with Article 220.127.116.11 ;
b) When a wall assembly with exposing building face is between 25 to 50%, is sprinklered throughout, installed on a gypsum board sheathing, and has a FSR not more than 25 (with restrictions) ;
c) When a wall assembly with exposing building face is between 50 to 100%, cladding can be combustible for group A, B, C, D, E, F.
§ When a building is required to be of non-combustible construction, combustible elements are limited to the requirements in Subsection 3.1.5 on non-combustible construction ;
§ When comparing the NBCC with the International Building Code (IBC), the IBC is more in favour of using FRT wood frame in-fill walls with one more storey.
Solutions for Mid-Rise Wood Construction: Full-Scale Standard Fire Test for Exterior Wall Assembly Using a Simulated Cross-Laminated Timber Wall Assembly with Interior Fire-Retardant-Treated Plywood Sheathing