Thermal Mass in Masonry

Words: John Cicciarelli
Photos: Echelon

A building’s exterior design and material selection impact all aspects of the final product, from indoor air quality to overall energy efficiency. When design-build teams aim to achieve a more energy-efficient building, material selection is the most crucial aspect of the process. The building material must have both optimal insulating value and thermal mass to achieve energy-saving goals.

Because of their inherent thermal mass, masonry products help reduce indoor temperatures and lessen the load on mechanical heating and cooling systems. This makes them an ideal choice for commercial and residential projects, enabling energy savings and future LEED certification.

Building with Masonry for Energy Savings
Masonry systems have a unique ability to enhance thermal performance while providing one of the best passive design options, according to the International Masonry Institute. The passive design, which performs over the building’s lifetime, combines building performance with heating and cooling requirements to create an efficient building envelope.

Load-bearing concrete masonry presents an efficient use of materials because the structural and aesthetic qualities are combined into a single building material. Efficient use of materials can be broken down into three categories:

Intent: Intent refers to the utilization of thermal mass to improve thermal efficiency and minimize environmental impact.
Proposed requirements: This refers to the provision that a wall system combines superior thermal mass with minimal maintenance, minimal cement content, and efficient utilization of all materials.
Design approach: This specifies post-tensioned, partially grouted exterior concrete masonry wall systems.

The energy-saving properties of concrete masonry can be demonstrated through a time vs. temperature chart. This chart covers a 24-hour cycle, which illustrates how a stud wall lags behind outside temperatures by approximately two hours. The concrete masonry wall, however, lags outside temperature by around six hours, enabling potential energy savings to heat or cool the building by pushing peak energy demand into off-peak hours.

Because masonry decreases the workload on HVAC systems, it leads to a reduction in insulation costs. As noted in ASHRAE 90.1, thermal mass works in conjunction with insulation to reduce thermal transfer, resulting in less insulation being required in a thermal mass solution compared to a stud wall. For instance, a typical wall R-value requirement of R-18 can be met by a high thermal mass masonry wall with an R-value of R-7.

Research has shown that thermal mass is most effective when used on the interior of the insulation in the building envelope. This includes load-bearing concrete masonry as part of a cavity wall system and interior concrete masonry walls and interior stone applications. The use of masonry and other building materials with thermal mass is well-suited for any project, but especially those in areas that experience hot and dry conditions during the day and cooler temperatures at night. Research conducted on residential projects shows that homes in hot, dry climates with exterior walls of high thermal mass require less energy for air conditioning than wood-framed houses with similar insulation but less thermal mass.

Not every building takes place in this type of climate, but there are advantages to constructing with masonry for thermal mass regardless of the environment. In variable climates that experience all four seasons, thermal mass reaps the most benefits during spring and fall. In these seasons, the building will be passively warmed and cooled. In areas that experience extreme cold, the thermal mass of masonry products helps store heat from daytime hours and reduces the need for mechanical systems to off-peak hours.

Masonry: A Single Solution for Energy Efficiency
Considering thermal mass in building design presents both environmental benefits, such as improving air quality and efficiency, and potential construction cost savings due to the need for reduced insulation and reduced energy usage over the building’s life cycle. Utilizing masonry wall systems for their thermal mass and added benefits, like moisture resistance and durability, means designers and builders can have a single building envelope solution that meets all their needs.

Thermal Mass in Masonry

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