Specifying Fire Resistance Ratings for Concrete Masonry Construction

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Building codes take a multifaceted approach to protecting life and property during a fire. These requirements address the combustibility, flame spread, smoke release, and structural stability of the systems that are used to mitigate the occurrence and spread of fire within buildings while allowing the safe evacuation of occupants. The inherent attributes of concrete masonry make it an ideal choice in meeting and exceeding the minimum building code requirements.¹

DETERMINING FIRE RESISTANCE RATINGS

In accordance with the International Building Code², the fire resistance of concrete masonry assemblies can be determined through one of multiple compliance options. These include:

PHYSICAL EVALUATION in accordance with ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials³.
CALCULATED fire resistance determined in accordance with Section 722 of the IBC. The calculated fire resistance method is an adaptation of the standard ACI/TMS 216.1⁴, Code Requirements for Determining Fire Resistance of Concrete and Masonry Construction Assemblies.
PRESCRIPTIVE DETAILING requirements in accordance with Section 721 of the IBC or a listing service⁵.
ALTERNATIVE MODELING OR DESIGNS based upon engineering analyses or alternative sources of documentation, research or testing.

The calculation method for determining the fire resistance rating of concrete masonry assemblies is by far the most common because it allows a nearly limitless combination of unit sizes and configurations,
combined with an array of aggregate types used in producing the concrete masonry units.

BEST PRACTICES FOR SPECIFYING FIRE RESISTANCE RATINGS

The calculated fire resistance rating is a function of two variables:

The equivalent thickness of the CMU
The type(s) of aggregate used in the production of the CMU.

Because neither may be known to the designer during the early
phases of design, it is best practice to simply specify the required fire resistance rating. Doing so ensures the lowest-cost options for a given market are leveraged for each project.

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Cost-Savings Strategies for Concrete Masonry Construction

Masonry construction has been around for millennia, and while masonry’s core attribute remains a handcrafted form of construction, there have been countless innovations through the decades covering all aspects of constituent materials, manufacturing technology, and design modeling that offer an array of efficiencies compared to how we designed and constructed masonry in past generations.

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Crack Control in Concrete Masonry Construction

For concrete masonry construction, existing codes and standards specifically address deflection limits and serviceability requirements for structural loading conditions to mitigate cracking. These documents do not, however, require prevention of cracking due to long-term shrinkage, only that it be considered. Instead, industry recommendations have been established to mitigate shrinkage-related cracking.

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Properties and Characteristics in Concrete Masonry Construction

A concrete masonry unit may, on the surface, appear to be an unassuming construction product cast of simple concrete, but the technology behind this fundamental building block incorporates more than a century of research, evaluation, and evolution behind it that yields the basic properties and characteristics inherent in what is commonly referred to as CMU.

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Moisture Control for Concrete Masonry Wall Construction

Effective moisture control in concrete masonry unit (CMU) walls requires the integration of quality materials, precise detailing and proper workmanship. The coordinated use of integral water repellents (IWR) in both block and mortar, along with flashing, weeps, joint tooling, and breathable coatings, prevents water intrusion, promotes drying and ensures long-term durability. Moisture management is not a single product but a system that must be specified and constructed correctly.

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Moisture Control, Performance

Sound Abatement and Concrete Masonry Construction

Quiet, comfortable, functional spaces start with CMU. Concrete masonry walls inherently reduce noise thanks to their mass — with no special detailing, finishes or channels required. Whether reducing traffic noise from outside or audibly separating rooms inside, CMU delivers reliable acoustic performance that enhances occupant comfort regardless of whether the performance objective is code-based or beyond code minimums to achieve wellness-centric sustainable metrics.

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Performance, Sound/Acoustics

Thermal Performance of Concrete Masonry Construction

Thermal performance is critical in building envelope design, and concrete masonry units (CMU) offer thermal mass that moderates indoor temperature swings and shifts heating and cooling loads to off-peak hours. CMU assemblies support varied insulation strategies, giving designers flexibility to meet energy codes and make performance-based decisions across building types.

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Performance, Sustainability, Thermal Performance

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Questions About Block?

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Fire

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Energy Efficiency and Thermal Mass