Designing Noncombustible Wall Assemblies

Article Description

An overview of the history of building codes and how they have impacted the design of wall assemblies. This seminar includes a discussion of the impact of fire tests on buildings using IBC, NBCC and ASHRAE 90.1 energy code requirements, the history of the IBC, NBCC and the definition of what building envelope components are combustible and require testing by the building code.

Project: The Linq Lofts + Flats 18151 68th Ave NE., Kenmore,
Washington by MainStreet Property Group LLC
Architect: Dahlin Group Architecture
General Contractors: GenCap Construction
Product: Longboard®  Cladding in Light Cherry
Photographer: Matthew Gallant

Article Objectives:

  1. Understand the history of the International Building Code (IBC) and who the main influencers are.
  2. Recognize how the fire and energy codes are impacting the design of wall assemblies.
  3. Identify the options for creating a code compliant wall assembly.
  4. Evaluate how the building code could influence the market for building and architectural materials now and in the future.

1   2   3

The Influencers

Understanding who’s in charge of the code and why certain safety and performance issues are emphasized can help give a better understanding of why and how the code was written. In the U.S. the code is written by a team of 50,000 members of the International Code Council (ICC) with only approximately one third of those members as regulators. The rest are builders, designers, manufacturers, and industry representatives. The ICC describes a democratic process of creating and changing codes. The ICC code-writing and revision process has a three-year cycle. If you want to propose a change to the code, then this proposal must be submitted 2 years before the next version comes out. In Canada, the Canadian Commission on Building and Fire Codes (CCBFC) develops and maintains Canada’s National Model Construction Codes using a similar process.  In Canada the National Research Council of Canada (NRC) and Canadian Commission on Building and Fire Codes (CCBFC) publishes the National Building Code of Canada (NBCC) every five years. The 2015 version of the NBCC has had over 600 technical changes incorporated into the new edition.

John Paul II Pastoral Centre
Architect: John Clark Architect Inc
Project Address: 4885 Saint John Paul II Way Vancouver, BC
Product: LONGBOARD® 6” V Groove in Light Cherry

When it comes to code development and changes the real movers and shakers are those with the time and money to follow the process. Specifically the insurance industry, large building-product manufacturers, and the government.  In the U.S. the National Association of Home Builders (NAHB) and in Canada the Canadian Home Builders Association (CHBA) act as the voices for most of the homebuilders who have seen building codes become more rigid due to safety concerns.

An Emphasis on Safety

Nine of the ten most costly catastrophes in the United States occurred in the 1990s. In 1992, catastrophes accounted for $22.97 billion of insured loss. In response to these catastrophes more stringent building codes were developed. From 2009 to 2012 we have seen more changes in the code than ever before and this pattern has continued into 2015 and now beyond. You know the old saying, “Those who don’t know history are doomed to repeat it.”, well in this case it seems the building community has taken great strides to prevent that from happening.

Maintaining the Codes

In the U.S. and Canada the government systems in place give the state or provincial authorities regulatory powers to execute building code standards. then within those authorities every city or municipality may have their own set of code standards. To try and create some uniformity building code writers began to create a national set of standards, however, these did not get implemented until 2000 when the International Building Code was created. In Canada the NRC’s Canadian Codes Centre (CCC) provides technical and administrative support to the CCBFC and its related committees, which are responsible for the development of Canada’s National Model Construction Codes since 1941.

“Not by accident are buildings built to be resistant to natural hazards such as earthquakes or wind. Good performance is the result of careful design and construction. Today’s engineering technology and knowledge is the equivalent of penicillin or a vaccine in being able to counteract a hazard and provide safety to the public. But this benefit is only delivered when our engineering know-how is implemented via building codes.”

Robert Reitherman, Executive Director, California Universities for Research in Earthquake Engineering

Arden by Bosa
Project Address: 738 Long Bridge Street, San Francisco, CA
Products: Longboard® 6 inch V-Groove in Cordoba Cherry
Developer: Bosa
Architect: Chris Dikeakos Architects Inc.,
Installer: Letner Roofing

Authority Having Jurisdiction (AHJs)

While many states and provinces adopt the standards of ICC’s I-Codes or the NBCC the district, city or municipal authorities may make their own amendments to the code meaning two neighbouring cities may have different code requirements. In addition, they may also choose which version of the building code to adopt as law for example the NBCC 2010 or the 2015.

Local law can become problematic when the local codes are dated or when building inspectors either don’t have the training or the latitude to apply logic to a situation. For example, in one Canadian city, an outdated section in the local building code caused problems for a local developer. A building inspector rejected the aluminum siding that was specified because it hadn’t been tested to a standard referenced in the code. The confusing part was the test the inspector was referring to no longer existed, since the local building code was referencing an earlier version of the NBCC. Consequently the manufacture could not engage in this testing even if they wanted to.

Fortunately, after some deliberation the problem was resolved and the originally specified siding was approved for use. This situation highlighted a key concern for manufactures, builders and architects, what if the local codes just don’t make sense? In addition to this, there are ASTM (American Standard for Testing and Materials) test standards and ULC (Underwriters’ Laboratories of Canada) test standards, in many cases the non-combustibility tests are very similar if not exactly the same. The National Building Code of Canada permits the AHJs to accept results of fire tests using either ASTM or ULC standards, however, not all jurisdictions allow ASTM to be used instead of ULC and vice versa for the U.S.

One tool which architects can use is an engineering judgment analysis letter furnished by a reputable code expert. Technically the legal responsibility doesn’t fall on the code officials, but rather the consultant and the party who commissioned the consultant. Usually the Authorities Having Jurisdiction (AHJs) are often willing to consider such well founded exemptions, or specific exemptions which will be included in future versions of the IBC or NBCC.


Determining Code Compliance

Noncombustible construction can be a misleading statement: it does not exclude the use of combustible materials it limits their use. Since it is neither economical nor practical to construct a building entirely out of noncombustible materials, some combustible materials can be used.

There are over a dozen different types of non-combustibility tests for wall assemblies and exterior wall cladding. Why the emphasis on exterior walls?

The Commonwealth Scientific and Industrial Research Organization (CSIRO) reviewed statistics related to exterior wall fires and found that exterior wall fires appear to account for somewhere between 1.3% and 3% of the total structure fires for all selected property types investigated. Furthermore, fire incidents involving exterior wall assemblies around the world were also reviewed and although exterior wall fires are low frequency events, the resulting consequences in regards to fire spread and property damage can be significantly high. The impact on life safety in terms of deaths was found to be relatively low with the main damage being caused by smoke exposure rather than direct flame or heat exposure. In addition to this, combustible exterior wall systems may also pose an increased fire hazard during installation and construction. Examples of this would be the 2009 CCTV Tower Fire and 2010 Shanghai fire in China.

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Location: Montana State University – Dining Hall
Architect: Mosaic Architecture
Photographer: Zakara Photography & Whitney Kamman Photography

Other Fire Rating Tests

ASTM E136 or CAN/ULCS114 –  Determines the non-combustibility of products 

CAN/ULC S102 is the Canadian version of ASTM E84 the building code makes allowances for ASTM standards since they are the same tests, however, this is always up to the Authority Having Jurisdiction

ASTM E84 or CAN/ULCS102 –Surface Burning Characteristics

Comparatively measures product surface flame spread and smoke density. Products are then classified as A, B, or C based upon their flame spread index, with Class A offering the lowest flame spread levels. It’s important to note that this test does not measure heat transmission, determine an assembly’s flame spread behavior, nor classify a material as noncombustible.

AST M E1354–Cone Calorimeter Test

A small sample specimen is taken and measured for heat of combustion, mass loss rate, time to sustained flaming, and smoke production. The test applies to various categories of products and is not limited to representing a single fire scenario.

ICC ES Reports

These evaluation reports are used to help determine if a building is code compliant and helps agencies enforce building regulations. Manufacturers also use these reports to provide that their products meet code requirements and warrant regulatory approval. This is particularly important for new and innovative products.

AST M E119/UL 263/IBC 703.2

Provides assembly measurement of the transmission of heat and hot gases while determining the load carrying ability during the test exposure. The test does not simulate scalability or fire behavior between building elements such as floor-wall or wall-wall connections. Nor does it measure the generation and movement of smoke through the assembly, generation of toxic gases, or flame spread over the surface.

NFPA 268–Radiant Ignitability of Assemblies

NFPA 268 tests for ignition of an exterior wall assembly by exposing it to a specified radiant heat flux for 20 minutes. The test is not used to evaluate a wall assembly’s fire endurance, surface flame spread, or the effect of fires originating from within the building, exterior wall assembly, or at the openings.

Enter the Energy Code

In the 2012 IECC and ASHRAE 90.1 2012, the mandated use of continuous insulation (c.i.) increased for every climate zone, which means (that for) 90% of the U.S. all commercial jobs must have exterior c.i..

Insulation is considered continuous when it is installed on the exterior side of the base wall in order to reduce the effect of thermal bridging on the overall R-value of the wall assembly. Specifiers are most familiar with foam insulation for its’ ease of use, cost effectiveness and its’ R-value. For example, mineral wool has a nominal R-value of about 4 per inch of material, and the type of foam plastic insulation recommended for exterior walls, namely extruded polystyrene, has an R-value of 5. For an even higher R-value, polyisocyanurate insulation is rated at 5.6 per inch.

So what does this all have to do with combustibility?

Foam is combustible and automatically triggers the need for the wall assembly to be tested to NFPA 285 or CAN/ULC S134(or CAN/ULC S101)

The benefit of mineral wool insulation is that it is noncombustible and will not prompt a NFPA 285 test. In addition to noncombustibility, mineral wool differs from foam plastics due to its high vapor permeability. This directly increases the wall’s ability to dry out if water gets into the wall assembly through a penetration leak or condensation from air transported moisture.

Essentially, the increasing use of exterior continuous insulation contributes to the growing complexity of designing exterior wall systems. Thickness, permeability, and location of the insulation in the wall assembly have an effect on how it responds to thermal air and moisture loads. 

There is no one single perfect wall design. The building science aspects of material properties, their locations in the wall assembly, the attachment methods, assembly performance requirements, constructibility, and climate conditions must all be considered in a high performance building envelope.

Designing NFPA 285-Compliant Building Envelope Systems

As mentioned, every configuration requires a separate test. So even if a specific WRB, cladding and insulation type were to pass the test, if the designer decides to swap out even one of the components, an entirely new test must be conducted.

For example, there are many types of foam plastics and performance varies, explains Beitel. “Based upon the wall assembly you put them into, some will pass and some will fail. That is the problem that the architects perceive they have. They want to use a given foam with a given veneer, but it has to pass the test.

“None of the foams have a perfect track record and that’s the confusing part here,” he adds.

In some cases, manufacturers who have tested various combinations of their products in wall assemblies, can be very helpful. So specifying a specific wall assembly which has already been tested by the manufacturer will obviously spare the architect the time and money for testing, which can amount to a savings of thousands of dollars, according to Vecchiarelli.

However, this means that every element of the wall assembly must be exactly the same as when it was tested and this, in turn, forces wall assemblies into a proprietary status, rendering them un-biddable. Consequently, to get around this, architects must now design their walls with multiple 285-compliant assemblies in mind.

Making the situation even more complicated: 

“Since the adoption of NFPA 285, many hundreds of wall assemblies have been tested with no specific guidance regarding joint placement. These tests have provided the design professional a broad range of test reports covering assemblies with anything from no vertical joints to the-now mandatory-vertical joint in the center of the window opening and with horizontal joints located practically anywhere on the wall assembly. Out of the hundreds of tests run over the past 20-plus years, only a small fraction have been done with joints in the newly defined locations. Each of these wall assemblies have met the test criteria at a test cost in the neighborhood of $25,000 or more when combining lab fees plus material and labor costs to construct the wall.

When the new NFPA 285 standard is published, most existing tests will no longer meet the requirements due to the new joint requirements, and a new test will need to be run on a wall assembly that has been accepted for decades. With only three or four recognized test facilities in North America, there will be a considerable backlog for new wall design tests, and to retest walls that were once considered acceptable. While the IBC may not reference the new test version of NFPA 285 until the 2021 code is published, architectural specifications can begin requiring these new test results almost as soon as the test standard is published.” 

Quote taken from article by Paul Deffenbaugh Editorial Director 

Recognizing this complexity, some initial efforts are being made to compile a database of 285 fire-tested assemblies. Meanwhile some proactive material manufactures are trying to offer a large selection of compliant assemblies that use their products for designers to choose from.

This is what the architects need at the end of the day,” affirms Beitel. “How soon and how that will come about, I don’t know as it is not a simple process, but the construction industry understands that we have to get that together.”

One tool which architects can potentially use is an engineering judgment analysis letter furnished by a reputable code expert. This involves bringing in such a consultant and inquiring as to whether individual products which passed NFPA 285 in separate tests, could be combined together in one assembly and not officially require testing, based upon the expert’s opinion that the new combination would theoretically provide acceptable life safety levels.

“It is possible and reasonable to make such judgments,” notes Beitel. “For example, if a steel stud gypsum wall was tested and passed, and now the architect wants to put it on a concrete masonry unit, the code officials would probably accept this.”

At the same time, such an engineering analysis must come from a consultant who is intimately familiar with the 285 test and is knowledgeable in the field. And secondly, the onus lies on the architect and consultant to convince the local AHJs that the NFPA 285 test can be bypassed in this instance.

“This can save a considerable amount of money over a custom 285 test. Of course, if a full test is going to be required, fire safety consultants are essential to get to approval without experimenting with the materials too much,” adds Altenhofen.

Since the legal responsibility doesn’t fall on the code officials, but rather the consultant and the party who commissioned the consultant, the AHJs are often willing to consider such well-founded exemptions, or specific exemptions which will be included in future versions of the IBC, such as the WRB exemptions in the 2015 IBC.

Other than recruiting the services of such a consultant, as mentioned, architects don’t have the benefit of a “cheat sheet” at this time and are really being forced to do their homework. At the same time, some manufacturers are more progressive than others in providing specifiers with such a chart instructing how to build a NFPA 285 compliant wall assembly based upon their testing data.

In addition to the NFPA 285 wall assembly test, relevant combustible components must also pass a series of material tests, per the International Building Code.

“It is important to understand the how material tests differ from assembly tests on how they are performed and how they are required by code,” says Benjamin Meyer, science architect, DuPont Building Innovations, Richmond, Virginia.

While, in many cases, the manufacturers take care of these tests, architects need to be familiar with the various ASTM tests and double check that a given product is compliant.

Designing Without NFPA 285

As noted earlier, if a wall assembly is designed without foam plastics and is less than 40 feet above grade, then NFPA 285 testing is not required. In addition, NFPA 285 compliance is not required for Type V Combustible Wall construction as the IBC gives prescriptive requirements instead. Previously, NFPA 285 compliance was not required for a wall of any height, comprised entirely of noncombustible materials, but the recent addition of the WRB trigger to the 2012 IBC has put a logistical hold on this option.

In terms of the WRB exceptions coming up in the 2015 IBC, although this code version won’t be adopted for some time—in fact, as late as 2018 in some jurisdictions—the document is available for reference at this time and some local authorities may choose to implement it, particularly those who are approached by the National Institute of Building Science and the Building Enclosure Technology and Environment Council—with support from the American Institute of Architects—who are actively lobbying the IBC and local AHJs that wall assemblies can be built to acceptable life safety standards without the full requirements of NFPA 285.

In particular, the group proposed changes to the foam insulation and WRB sections of NFPA 285 for the 2015 IBC. Although the foam proposals were rejected, the group achieved partial success with WRBs.

The specific claim made by NIBS/BETEC in the WRB proposal reads as follows:

“There are materials that are available, tried and tested by long-term proven history of performance as weather barriers that are not able to meet the standards in this test. Section 1403.2 of the IBC requires weather-resistive barriers while Section 1403.5 requires them to be tested to a standard if they contain a combustible water resistive barrier that many materials that are traditionally used and have proven their value can’t meet.

Section 2603.5 establishes requirements for protection and testing of combustible water resistive barriers that include foam plastic insulation, so Section 1403.5 is not necessary for those products. Given that 75% of construction litigation relates to water leakage suggests that this paragraph should be deleted or we are likely to face significant problems in the future with the failure of exterior water barriers.”

A New Reality

Although NIBS and BETEC are planning to continue lobbying the IBC, and it will take time until all the local AHJs update their codes to incorporate the 2012 IBC, or at least base their next commercial building code on the latest IBC, the fact remains that the construction industry is entering a new NFPA 285 reality. These stringent fire protection provisions coupled with stricter energy codes are anticipated to shake things up in terms of the way wall assemblies will be specified moving forward.

Tasked with this challenge, architects will need to be knowledgeable about the standard, how it works, when it is applied, and when it can be avoided. Meanwhile, manufacturers who want their products to be specified will have to work as an ally to designers by taking on the onus of testing, where possible, and openly furnish architects with test-compliant information.

This document draws out some of the main points from the NBC regarding fire protection of exterior walls incorporating combustible components, claddings or cladding elements. Foamed plastic insulations, which typically have flame spread ratings between 200 and 500 (depending upon the type), cannot be left exposed anywhere on the interior or exterior of a building. For exterior applications, foamed plastics used as part of an exterior wall must be tested to, and comply with, the full scale fire test CAN/ULC-S134. Materials must comply with CAN/ULC-S102 “Standard for Surface Burning Characteristics of Building Materials and Assemblies” in preference to ASTM E84 “Standard for Surface Burning Characteristics of Building Materials”.

There are a number of provisions within the NBC that relate to fire protection of exterior walls incorporating combustible components, claddings or cladding elements. Section addresses the protection of combustible components of exterior walls from external fire attack. Section ‘Combustible Components for Exterior Walls’ require exterior non-load bearing wall assemblies that include combustible components are permitted to be used in a building required to be of noncombustible construction provided that:

(a) the building is (i) not more than 3 storeys in height, or (ii) sprinklered throughout,

(b) the interior surfaces of the wall assembly are protected by an approved thermal barrier and

(c) the wall assembly satisfies specific criteria when subjected to testing in conformance with CAN/ULC-S134, “Fire Test of Exterior Wall Assemblies.”

Conversely, addresses the protection of combustible insulation within the wall, or used as an interior finish, from interior fire spread. Section applies to combustible insulation and its protection. Foamed plastics having a flame-spread rating of not more than 500 may be allowed in a building required to be of noncombustible construction when protected by an approved thermal barrier.

Section applies to minimum construction requirements for exposing building faces based on the occupancy classification of the building. The fire resistance ratings which are required will depend on the area of unprotected openings as a percentage of the exposed building face and the spatial separation to adjacent structures.

Section states that foamed plastic insulation used in exterior walls greater than 3 stories where the maximum area of unprotected openings is permitted to be greater than 10% must be protected by a minimum thickness of 25 mm concrete or masonry or pass a modified version of the CAN/ULC-S101 fire endurance test, as well as other performance requirements.

The performance of exterior walls during fire exposure is a critical element of building construction. Steel, concrete, masonry, gypsum and stone wool are the materials of choice when fire performance and the presence of combustible materials within the building envelope are of concern.

The federal government has been aggressively raising the bar on energy-efficient building standards, making this sustainable trend a requirement.

The DOE has mandated that by October 18, 2013, all states must certify that they will adopt a commercial building energy code that meets or exceeds ASHRAE Standard 90.1-2010. This updated standard triggers the need for a substantial change to the design of wall assemblies in new commercial construction.

National Energy Code of Canada 2015

IECC 2012

The 2012 International Energy Conservation Code (IECC), which adopts ASHRAE Standard 90.1-2010, has increased the minimum thickness required for continuous insulation for most commercial wall assemblies in climate zones 3 – 8, approximately 90 percent of the United States.

Map of the US climate zones according to the IECC

Whereas previous codes have only alluded to general air sealing of the building envelope, the 2012 IECC now includes specific, mandatory provisions for Air Barriers in Climate Zones 4-8. These requirements may be met through the use of approved materials, approved assemblies, or whole building air leakage testing (ASTM E779). As more states adopt this code, these provisions will become mandatory for designers of commercial buildings in those jurisdictions.

Typically revised every three years, the IECC is part of the International Building Code (IBC) and is the governing commercial code section for building design and material requirements related to energy efficiency.


The IECC divides the United States into eight climate zones, each with specific requirements for the type, placement and amount of insulating materials – both cavity and continuous – in the wall assembly. Several versions of the IECC are currently in effect across the country, making it vital to be aware of which version is adopted by the state or local jurisdiction in which a project is located.


Each update of ASHRAE Standard 90.1 and IECC adoption has increased the amount of continuous insulation required in commercial buildings.

The latest ASHRAE Standard 189.1 (Standard for the Design of High Performance Green Buildings) adds the requirement for an air barrier as well as requiring and increasing the thickness of CI in ALL climate zones (1-8).

There is little doubt that future codes will be even more stringent when pertaining to energy efficiency.


Keeping up with code changes requires a commitment to researching how code changes are driven by either technology or new knowledge and experience that suggest a better way to do things. In some cases a code will incorporate something new, only to learn it doesn’t work, so three years later it gets changed back to the way it was. Therefore, the building code standards can be a bit of a moving target and will require a commitment to keep on top of the latest in code changes, reviews and challenges.

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