The following new BC Building Code provisions were enacted by Ministerial Order in early January 2009 and took effect on April 6, 2009: (click here for Ministerial Order)
On April 3, 2009, a new seismic safety provision was added as a result of ongoing research and analysis.
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Article 3.2.2.45 of the BCBC specifically addresses the construction of combustible (wood) buildings up to four storeys. The code change increases the permitted height of these buildings to six storeys. Additional requirements include:
Article 3.1.4.1.(4) of the BCBC reduces the risk of external fire spread by limiting the combustibility of cladding.
Subsection 4.1.8 of the BCBC addresses earthquake load and effects.
Article 4.1.8.10 places restrictions on the configuration of timber shear wall systems.
New language in Articles 4.1.8.11 & .12 establishes acceptable seismic design force levels specifically for 5-and 6-storey wood-frame buildings.
Article 3.1.8.12 of the BCBC addresses electromagnetic hold-open door devices that release during a fire. The proposed code change would allow hold-open devices on fire doors in public corridors.
Appendix Note to Subsection 4.3.1 of the BCBC, which addresses design requirements for structural materials. Appendix notes are used to provide additional information on code requirements. The appendix note focuses on the need to consider shrinkage of wood in structural design.
Changes and additions to the BC Building Code are displayed in green.
Click on the section headers below to flip back and forth between the different sections of the new provisions.
This code change for building height requires that buildings built under 3.2.2.45 are less than 18 metres to the uppermost floor level of the top storey, which precludes the use of top floor mezzanines to achieve additional height without triggering high building requirements.
1) A building classified as Group C is permitted to conform to Sentence (2) provided
b) it is not more than 6 storeys in building height, and
c) has a maximum height of less than 18 m measured between grade and the uppermost floor level of the top storey, and
To limit the overall height of combustible buildings and restrict buildings under Article 3.2.2.45 from being built as high buildings as defined by the BC Building Code (Subsection 3.2.6).
This code change for building area defines the total permissible building area for each floor of a five and six-storey wood-frame building.
1) A building classified as Group C is permitted to conform to Sentence (2) provided
d) it has a building area not more than:
The BC Building Code addresses the inherent difference between combustible and noncombustible construction by limiting combustible building area to 20% of that permitted for a noncombustible building of similar height. This factor is maintained in this proposal.
Article 3.2.2.45 currently employs a formula in apportioning building area relative to the building height, such that the resulting gross floor area is limited to a maximum of 7200 m2:
Under the new provision, the total floor area of 7200 m2 currently in existence will be kept for the five and six storey sub-clauses, resulting in:
By maintaining the same gross floor area, the following risks will not likely increase:
The same gross floor area and the same fire engineering philosophy of compartmentalization and sprinkler protection results in the probability of no additional fire risk in these areas.
Combustion-resistant exterior cladding can protect a building from exterior fire spread. This code change for exterior cladding materials establishes fire-resistance requirements for exterior cladding on mid-rise wood frame buildings. Only noncombustible material must used where it is required by the spatial separation provisions of the code.
3) Except as required in Sentence (4), a building referred to in Subclause 3.2.2.45.(1)(d)(v) or (vi) shall
a) have an exterior wall cladding which
i) is noncombustible,
ii) has the exterior wall assembly constructed such that the interior surfaces of the wall assembly are protected by a thermal barrier conforming to Sentence 3.1.5.12.(3), and the wall assembly satisfies the criteria of Sentences 3.1.5.5.(2) and (3) when subjected to testing in conformance with CAN/ULC-S134, “Fire Test of Exterior Wall Assemblies”, or
iii) is fire retardant treated wood tested for fire exposure after the cladding has been subjected to an accelerated weather test as specified in ASTM D 2898 “Accelerated weathering of Fire-Retardant-Treated Wood for Fire Testing.”
4) Sub-clauses 3.2.2.45.(3)(a)(ii) and (iii) are not permitted where an exposing building face is required by Article 3.2.3.7. to have noncombustible cladding.
Re-number existing Sentences (3) & (4) to Sentences (5) & (6).
Establishing performance-based fire-resistance requirements for exterior cladding will reduce the probability of ignition of the building face which could result in exposure conditions to adjacent buildings and fire spread beyond the compartment of origin. Where the code currently requires noncombustible cladding, fire-resistant combustible cladding will not be allowed.
Shear walls provide resistance to lateral earthquake loads. This code change for shear walls provides direction to the structural engineer on designing and locating shear walls.
4) In cases where IEFaSa(0.2) is equal to or greater than 0.35, for buildings constructed with 5 or 6 storeys of continuous combustible construction as permitted by Article 3.2.2.45 and having any fundamental lateral period, Ta, walls forming part of the SFRS within the continuous combustible construction shall not have irregularities of Type 4 or 5 as described in Table 4.1.8.6.
Further work is being undertaken to understand seismic behaviour of mid-rise structures of entirely wood construction. This code provision prohibits certain types of irregularity in a shear wall system so that expected responses of this type of structure are maintained at reasonable levels by well-defined lateral-load resisting systems. In-plane discontinuity and out-of-plane offset in a timber shear wall system will not be allowed over the entire height of a mid-rise timber structure. For a building consisting of a mid-rise timber structure on top of above-grade reinforced concrete construction, this requirement applies to the timber structure portion of the building. This conservative approach will be reviewed as more research data become available.
To introduce a lower limit on the seismic design force level specifically for 5-and 6-storey wood-frame buildings:
Where the fundamental lateral period, Ta, is determined by 4.1.8.11.(3)(d) for buildings constructed with 5 or 6 storeys of continuous combustible construction as permitted by Article 3.2.2.45. and having an SFRS of nailed shear walls with wood-based panels, the lateral earthquake force, V, as determined in Sentence (2) shall be multiplied by 1.2.
Except as required by Sentence (7) or (10), if the base shear, Vd, obtained in Sentence (5) is less than 80% of the lateral earthquake design force, V, of Article 4.1.8.11., Vd shall be taken as 0.8V.
The base shear Vd shall be taken as 100% of the lateral earthquake design force, V, as determined by Article 4.1.8.11. for buildings
The change reduces the risk of soft-storey seismic behaviour (building collapse) by restricting seismic design force levels specifically for 5- and 6-storey wood-frame buildings.
The code change allows hold-open devices on fire doors within a public corridor.
1) A hold-open device is permitted on a door in a required fire separation, other than an exit stair door in a building more than 3 storeys in building height, and on a door for a vestibule required by Article 3.3.5.7., provided the device is designed to release the door in conformance with Sentences (2), (3) and (4).
The change allows all doors within a fire separation to be held open with electromagnetic hold-open devices provided they are not serving an exit stair. The previous restriction applying to all exit doors did not take into account the fact that smoke/fire migration due to stack effect are not relevant to doors in horizontal exits located on the same storey.
This change has a positive impact in reducing the possibility of horizontal exit fire doors being blocked open using door wedges or other devices which will not automatically release when fire detectors register a fire threat.
This appendix note focuses on the matter of shrinkage, particularly in taller wood-frame buildings.
4.3.1. Wood (See Appendix A)
A-4.3.1. Wood
The design criteria for wood, CAN/CSA 086 “Engineering Design in Wood”, makes assumptions that the wood products being used are in a condition as intended by their grading. This includes the limits of moisture content as specified by the grade. However, conditions such as transportation, site storage, and construction conditions can impact the original design assumptions.
Design considerations should include and be specific to shrinkage that may occur due to changes in moisture content of the wood. This is of particular concern where the building height can be up to 6 storeys, such as being built under Article 3.2.2.45. The potential building movement due to shrinkage should be indicated to other design professionals for their considerations such as cladding systems and mechanical systems, hold-down devices for structural walls and connections to non-shrinking elements including firewalls and elevator shafts.
Shrinkage must be a design consideration in wood-frame construction, particularly for buildings of five and six storeys in building height. Shrinkage parameters should be coordinated among design professionals of the other impacted building systems.
