Figure 2: Images from a recent CAN/ULC S-134 test of architectural cladding system.
Combustible Cladding Options Under the Code
3.1.5.5 of the Code is not entirely clear and a rational explanation of how it should be applied is difficult once different sections and their intent are applied in the context of spatial separation as well as other issues including thermal protection of foamed plastics. That said this bulletin summarises what applies in the vast majority of cases.
Under 3.1.5.5. (1) the use of combustible cladding on unsprinklered non-combustible buildings is limited to 3 storeys- the typical walk up apartment building for instance. Where sprinklered, the use is restricted to:
Assemblies where any foamed plastics are protected by a thermal barrier- on the inside of the building.
Wall assemblies that pass the criteria of 3.1.5.5 (3) and (4) when tested in conformance with the CAN/ULC S-134 “Fire Test of Exterior Wall Assemblies. These sentences are essentially the pass criteria of the S-134 test. It should be noted that the S-134 test does not test assemblies in combustible construction such as wood frame. What this means is that where combustible construction is permissible, it is acceptable to use an S-134 system on the outside of the assembly as it does not significantly reduce the cladding performance if the S-134 pass criteria have been satisfied. The system has to include the complete assembly including the 5/8inch exterior GWB.
Based on sentence 3.1.5.5.(1), fire retardant treated wood would not satisfy the pass criteria of sentence (3) and (4) as heat release of FRTW is too high. Sentence (5) however, essentially permits it despite the restriction under the above pass criteria. Also, 3.2.2.50 of the BC Building Code 2012 for 5 and 6 storey sprinklered buildings, permits both FRTW or an assembly that satisfies the CAN/ULC S-134 criteria and has a thermal barrier on the inside.
Based on the code wording FRTW would be permitted without a thermal barrier unless the assembly incorporates foamed plastic requiring thermal protection.
An assembly tested to the CAN/ULC S-134 would require both a thermal barrier on the inside as well as the external GWB typically incorporated as part of the test assembly. This would be standard practice in wood frame applications where there is often foamed plastic in the wall cavity. However, if used in non-combustible applications without foamed plastic insulation then this would seem to be unjustified.
Going back to the requirements pertaining to combustible cladding in non-combustible construction there is an exception under 3.1.5.5.(2): where table 3.2.3.7 requires non-combustible cladding.
However, there are various exceptions to the requirement for non-combustible cladding and the main restriction is where the permissible openings are less than 10%. In this case cladding must be non-combustible. As such an S-134 tested system would not be acceptable. This is clarified in the Appendix A of Division B Part 3.
Where the openings permitted are at least 10% then 3.2.3.7 (3) defers back to the S-134 pass criteria set out in 3.2.5.5 which we just reviewed.
Where openings are more than 25% and less than 50% FRTW can be used under certain conditions provided the limiting distance is at least 5m and cladding meets the Part 9 requirements. Also, there is also a general cross reference in 3.2.3.7.(5) back to 3.1.5.5 provided the permissible openings are more than 10% and not more than 25%.
Given the ways these sections are laid out it is not surprising that there is confusion over how different requirements are intended to apply.
Foamed Plastic in the Exterior Building Face
There is a series of requirements under 3.2.3.8 setting out criteria for protection of foamed plastic in the exposing building face; however, assemblies that comply with 3.1.5.5 (S-134 etc. again) do not require to meet the requirements set out in 3.2.3.8 sentences (1) and (2). This is confusing as we have seen that a thermal barrier is specified in the requirements for 6 storey wood frame construction. It appears that the 3.2.2.50 requirements anticipated foamed plastic use and therefore have required it under 3.2.3.8 sentence (3). This also applies under 3.1.5.5 (1) (b)
It should however also be noted that fire blocks are required in exterior walls as per 3.1.11- Fire Blocks in Concealed Spaces. Essentially, this requires fire blocking at each storey and every 20m horizontally unless the insulation is either non-combustible or has a flame spread not more than 25 and has vertical firestopping every 10m vertically. Where there is an air space there should be only one air space and the maximum depth of this should be 25mm (1in.)
Composite Panel Systems
There are several manufacturers that have successfully subjected their systems to the CAN/ULC S-134 test. These systems are designed for use in non-combustible construction but can be used in combustible construction and will not adversely affect the performance of the wall assembly-even if wood frame. The assembly for non-combustible construction consists of:
If the wall is of combustible construction then it is common to use double- walled construction with insulated cavity walls for energy conservation. Where the wall requires a rating, this is typically provided by 1 or more layers of gypsum wallboard on the room side.
Where foamed plastic is sprayed in place for insulation and thermal performance of the wall the foamed plastic in combustible construction typically requires a thermal barrier with certain exceptions.
In non-combustible construction the exterior requirements are more complex but generally:
In most circumstances except for unsprinklered buildings over 18m a thermal barrier of 12.7 (0.5 in.) is required.
Adjacent spaces in wall assemblies are exempted.
For unsprinklered buildings over 18m the board has to be taped and filled- partly due to potential smoke spread.
Attics, interior walls and ceiling assemblies in unsprinklered buildings over 18m have thermal protection increased to 15.9mm thermal barriers taped and filled.
Factory- assembled wall units are dealt with separately.
Examples of a Composite Panel/Architectural Cladding System.
Generally composite panel system consists of the following components. The following are based on the AL13 architectural cladding system.
