The Use of Combustible Materials in the Building Envelope
Defining moments like the Grenfell Tower Fire challenge us to reflect on our responsibilities, our profession and the regulatory framework that supports the built environment.
We are reminded that the Architects Act, in tandem with building codes, serve to protect the public. We are called to acknowledge the privilege of self-regulation and the specialized training, obligations and ethics rooted in the profession.
Ultimately, the public depends upon architects engaged in the erection or alteration of buildings, and it is our duty to maintain our knowledge base and exercise responsibility with judgement and independence.
This Regulatory Review article has been prepared by the AIBC Building Envelope Committee to alert registrants to some of the issues coming out of the tragic Grenfell Tower Fire, and highlight some of the duties and responsibilities of architects in the design of cladding systems, both for new buildings and for the rehabilitation of existing buildings.
A Commission of Inquiry into the Grenfell fire has been set up to investigate and make recommendations. Inquiry findings, when published, will be shared with members.
On June 14, 2017, a fire occurred at the 24 storey, 67 metre high, Grenfell Tower apartment building in London, England. More than 70 people were killed in the building fire, or succumbed to their injuries afterwards. The building was a 1960’s built concrete frame structure with concrete spandrel panels. It had recently been re-clad and re-glazed.
According to reports, the fire broke out inside a suite on the fourth floor. The fire broke through the window opening and proceeded up the side of the building in a very short period of time. In less than 15 minutes the entire structure was engaged in fire, both on the exterior and the interior.
The Grenfell Tower did not have automatic fire sprinklers. There was only one exit stair for the building, and the doors to access the exit stair were not functioning properly. Fire separations within the building may not have functioned, or were not in place.
The media has repeatedly pointed to the use of combustible aluminum cladding as the cause of the fire spread.
Based on unofficial media reports, we believe that the wall assembly was as follows:
- Cladding: Reynobond composite aluminum panel cladding with polyethylene core.*
- Substructure: Steel girts and steel sub girts resulting in a 50 mm air gap.
- Insulation: 150 mm Celotex RS5000 polyisocyanurate insulation or Kingspan Kooltherm K15 polyisocyanurate insulation.*
- Moisture Barrier: Unknown at this time, possibly self-adhered SBS on polyethylene carrier.*
- Back-up Wall: 200 mm concrete spandrel and concrete columns.
- Interior Finish: Assumed to be gypsum drywall on steel stud or hat track.
- Glazing: New aluminum frame windows were installed. The placement of the original glazing system was in line with the exterior concrete structure. The new glazing system was located outboard of the primary structure in line with the new 150 mm layer of insulation. We assume the windows were fixed to secondary structure tied back to the primary structure.
* This material is combustible
The building code Part 3 requirements, which address fire spread in buildings, are a key component of the code’s provisions for life safety. Architects need to be aware of their responsibility to design exterior envelopes that meet the code’s requirements for the control of fire in and through the cladding system. They also need to be aware that the use of foam plastic insulation both inside the building and within the building envelope is restricted by the code.
Where the insulation, cladding and cladding support includes combustible materials such as foam plastic insulation, special care must be taken to confirm that they meet the requirements of the code. Use of combustible insulation usually requires full systems fire testing to CAN/ULC S134 Fire Test of Exterior Wall Assemblies.
The building codes applicable in the province, the BC Building Code (BCBC), Vancouver’s Building Bylaw (VBBL), and the National Building Code of Canada (NBCC), include measures such as at least two exit systems, as well as automatic fire sprinklers, to prevent the type of outcome experienced at Grenfell Tower for new buildings.
It is important to note however that many older buildings do not have sprinklers. In these instances, recladding and other renovations to these buildings require attention to provisions for the use of combustible materials in non-combustible assemblies.
Architects are responsible for the application of Part 3 of the BCBC, VBBL, and NBCC, and should review Subsections 3.1.5 and 3.1.11. Particularly relevant are 18.104.22.168., 22.214.171.124. and 126.96.36.199., which deal with the use of combustible materials in cladding system for a building required to be of non-combustible construction.
Subsection 3.1.11., Fire Blocks in Concealed Spaces, is also important to consider. Based on National Research Council (NRC) research, limiting cavities in walls to 25 mm stops the ‘chimney’ effect and limits fire spread risk.
Any assembly containing combustible products which is planned to be used in buildings requiring non-combustible construction require further detailed investigation and possibly testing to meet CAN ULC S-134.
Composite Aluminum Cladding
Many high rise and other non-combustible buildings have been clad in composite aluminum panel systems. The material consists of an outer face of aluminum (1 mm thick) a core (3 mm, 5 mm or 6 mm thick) and an inner face of aluminum (1 mm thick). The core can be either combustible (PE Core) polyethylene or non-combustible (FR Core) sheet material (mineral filled polymer). It is the responsibility of the architect to specify the cladding system and check, where required, that the non-combustible and appropriately tested system is installed.
Foam Plastic Insulation
Use of foam plastic insulation is not permitted in non-combustible construction, except as allowed under specific conditions. Architects must apply the requirements of the code thoroughly in these cases, as these exceptions contain specific limitations on the extent and containment of envelope compartments. For example, compartments must be fire stopped at floors and closed around openings for windows.
It has been noted that the depth of the cavity between the cladding and insulation in the Grenfell Tower envelope system was 50 mm or larger. It is hypothesized that the large cavity created a chimney effect, which amplified the fire temperature causing the foam insulation behind the cladding to contribute to the fire.
Secondary Structure to Cladding
The secondary structure includes steel or aluminum girts, clips, channels and other elements that transfer the cladding loads to the primary structure. The use of combustible elements in these systems must be limited. In the event these elements burn or melt, the cladding system must stay in place.
Plastic Shims Blocking and Backing
In most cases, the shimming of the cladding system can be accomplished with non-combustible components. The use of combustible shims in these systems must be limited. In the event these shims burn or melt, the cladding system must stay in place.
Thermal Isolation Devices
High R-value envelope systems utilize thermal isolation devices to restrict heat transfer though high conductivity elements such as cladding support girts. The combustibility of these elements needs to be considered as it relates to maintaining cladding in place during a fire.
The Role of the Architect in Design and Post Design Phases
In British Columbia, in addition to the architect’s responsibility for the design of the building enclosure, including the cladding system, the BCBC and VBBL require field review during construction of Part 3 buildings to verify that the work is constructed substantially as designed. AIBC Bulletin 90: Minimum Scope of Architectural Services includes field review in the minimum scope of architectural services for buildings of any size.
During construction, owners are often presented with “value engineering” decisions. This is especially prevalent in residential construction and design build projects where costs savings during construction are expected. Changes in envelope materials and assemblies must be rigorously evaluated by the architect (as they would be in the design phase) to confirm that they do not compromise code the requirements.
The architect, owner and constructor need to work together to manage changes in the design during construction to avoid non-conforming substitutions of materials and their arrangements on site. The architect’s review of the shop drawings and materials submittals must include verification that the code requirements called for in the design are included in the fabricator’s proposed materials and assemblies.
Once on site, the architect’s review must include verification that the code requirements called for in the design are included in the constructor’s materials and assemblies. This is especially important where combustible materials are being used in non-combustible construction.
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