Producers are accustomed to promoting concrete based on durability, strength, and cost effectiveness. But concrete also contributes to the energy efficiency of a building, which can lead to energy savings during its use. As sustainable designs get more sophisticated and energy conservation requirements become more stringent, designers and owners prefer more energy-efficient materials.
Owners can increase their buildings’ energy efficiency by following energy codes, such as the International Energy Conservation Code (IECC) — part of the International Code Council (ICC) family of codes — which “establishes minimum regulations for energy efficient building.”
As I attended the 2015 IECC code-change hearings, I realized concrete and masonry products contribute to energy efficiency in specific ways that aren’t promoted heavily by the concrete industry. Producers should remind energy-conscious owners and architects of two fundamental concepts: thermal mass and air infiltration.
Most people understand that the greater the R-value of a material, the less heat or cold that passes through it. These R-values (also called thermal resistances) are determined by steady-state tests. But increasing R-values isn’t the only way to improve energy efficiency. Heat capacity also plays a big role.
In energy codes, whether a material is considered to have mass is determined by its heat capacity, or its ability to store heat. Because of concrete’s heat capacity, it has thermal mass. Thus, the minimum thermal resistance (R-value) required for mass elements (walls and floors) is less than that of other types of construction.
Concrete’s inherent mass helps meet increasingly stringent energy efficiency requirements with less added insulation. Other construction materials are now having to change basic construction methods (2x6 walls, or extended fasteners for cladding over exterior continuous insulation) to meet code minimums.
The amount of air that passes through a building envelope greatly influences the amount of energy needed to heat or cool that building. Although the amount of air that leaks into or out of a building depends on many factors (such as building height and temperature differentials), the materials, joints, and penetrations through the envelope also contribute to the amount of air infiltration. This is recognized in the 2012 IECC mandatory section C402.4 on Air Leakage.
When providing a continuous air barrier as part of section C402.4.1, there are three options for demonstrating compliance: materials, assemblies, or a building test. Cast-in-place and precast concrete are listed as compliant materials. If used, these materials do not need to undergo any additional testing to prove they demonstrate compliance, provided “joints are sealed and materials are installed as air barriers in accordance with the manufacturer’s instructions.”
This means designers can focus on other areas of the envelope when meeting IECC requirements.
When it comes to sustainability, popular benefits of concrete include supporting the local economy, using easily accessible and abundant resources, and durability or resilience. But when concrete is part of the building envelope system, designers can also save energy more easily with the same durable concrete producers have always provided.