Fire Safety and Code Challenges for Mass Timber in Curtain Wall Systems

Negotiating codes for a sustainable design



Photo of David Barber

David Barber



Photo of John Neary

John Neary

Senior Associate, Senior Facade Specialist


Photo of Mic Patterson PhD LEED AP+

Mic Patterson PhD LEED AP+

Ambassador of Innovation & Collaboration

Facade Tectonics Institute, Inc.



With the desire for more sustainable construction and reduced embodied energy, mass timber is being explored for building structures. For medium and high-rise buildings, timber has typically not been considered for curtain and window wall mullions and transoms. A curtain wall solution that uses mass timber (glulam) for the mullions and transoms is introduced, developed and analyzed here. While combustible, the inherent fire resistance provided by mass timber building elements greater than 6”, such as glulam, are distinctly different from the minimal fire resistance of light timber frame or aluminum members. Mass timber has flammability criteria that can meet the International Building Code (IBC) without additional topical treatment. There is potentially a code compliant path to use mass timber as part of a curtain or window wall within a medium or high-rise building, though the path is difficult to determine, involving IBC Chapters 6, 7, 8, 14 and 23, which indicates the level of complexity of the problem. This paper explores a potential IBC compliant path for the use of timber within a curtain or window wall system, provided the limits of the Code are followed, which can be an approvable solution. A timber curtain wall solution is discussed and detailed to illustrate how timber can be used to reduce a building’s embodied carbon, improve the warmth and aesthetics. The paper also aims to remove some of the confusion regarding required and relevant fire tests for interior timber systems.


Wood is a viable alternative to aluminum in curtain wall framing applications, with the potential for embodied carbon reductions in building skins (Patterson, 2017). The development of multi-story buildings utilizing

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Timber as a Material of Interest

Timber is among the oldest of building materials and has a long history of use throughout North America. Timber construction peaked during the North American trade expansion in the late

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Building Code Challenges and Solutions

All 50 states within the US adopt the International Code Council (ICC) International Building Code (IBC) (ICC, 2018), with some states also adopting the National Fire Protection Association (NFPA) Life

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Fire Fundamentals

Where a building element is load-bearing or separates one area from another and a fire resistance rating (FRR) may be needed, depending on the Building Construction Type, combustible and non-combustible

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Code Approach

Where timber is being used interior to the line of glazing as part of a curtain wall for example, the elements of the curtain wall need to be defined. The

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Fire Test Requirements

There are a range of fire tests listed within the IBC, but only one is applicable to timber being used as part of an interior window system: ASTM E84 “Standard

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Other Design Challenges

An area requiring thought and detailing is the slab-edge fire-stopping for curtainwall systems, required by IBC 715.4, where an assembly will be tested in accordance with ASTM E2307 (ASTM, 2019)

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A Conceptual Solution

The curtain wall system incorporating timber mullions and transoms proposed here takes wind forces and the weight of the wall assembly back to the structural floors. It incorporates an aluminum

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Summary & Conclusions

The need for buildings to reduce embodied carbon impacts and embrace and use more sustainable building elements has led to greater experimentation with materials. Timber has emerged as a material

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Thanks to Mr. Gianni Stramandinoli from Giugiaro Architettura and Structures for his inspirational design.

Rights and Permissions

American Society for Testing and Materials (ASTM), 2015, “ASTM E84: Standard Test Method for Surface Burning Characteristics of Building Materials”

Arup, 2019 “Rethinking Timber Buildings” (

ASTM, 2016, “ASTM E119: Standard Test Methods for Fire Tests of Building Construction and Materials”

ASTM, 2019, “ASTM E2307: Standard Test Method for Determining Fire Resistance of Perimeter Fire Barriers Using Intermediate-Scale, Multi-story Test Apparatus”

Architecture 2030 n.d. “Why the Building Sector?”, Accessed 28 July 2019:

AWC (American Wood Council), 2018a, “National Design Specification for Wood Construction”, Leesburg, Virginia

AWC, 2018b, “Calculating the Fire Resistance of Exposed Wood Members, Technical Report No. 10”, Leesburg, Virginia

AWC, 2019, “DCA 1 - Flame Spread Performance of Wood Products Used for Interior Finish”, Leesburg, Virginia

Cheung, Leo, and Mirko Farnetani, 2016, “Case study 2: Whole life carbon – curtain walling. In Targeting zero: Embodied and Whole Life Carbon explained”, Simon Sturgis, 35-40. RIBA Publishing.

International Code Council, 2018, “International Building Code”

National Fire Protection Association (NFPA), 2018, “Life Safety Code” NFPA 101

NFPA, 2017, “NFPA 268: Standard Test Method for Determining Ignitability of Exterior Wall Assemblies Using a Radiant Heat Energy Source”

NFPA, 2019, “NFPA 285: Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components”

Patterson, M., 2011, “Structural Glass Facades and Enclosures”, Wiley

Patterson, M., Kensek, K., Noble, D., 2017 “Supple Skins: Considering the Relevance, Scalability, and Design Strategies for Facade System Resilience”, Journal of Architectural Education 71 (1), 34-45

Petersen, Ann Kristin, and Birger Solberg, 2002, “Greenhouse gas emissions, life-cycle inventory and cost-efficiency of using laminated wood instead of steel construction: Case: beams at Gardermoen airport”, Environmental Science & Policy 5, no. 2: 169-182

Inventory of Carbon and Energy, University of Bath, Accessed 28 July, 2019: