It has been nearly two decades since the U.S. Green Building Council (USGBC) first unveiled the Leadership in Energy and Environmental Design (LEED) rating system in 2000, reinvigorating sustainable building with a benchmarking system for the design and construction communities. Initially, pursuing a LEED rating was often a matter of counting points and checking boxes, but the industry has since evolved. LEED ushered a transformation in thinking about how buildings are planned, constructed, maintained, and operated, and the industry has run with it. Now, we are building holistically with a systemic approach to optimizing building performance by minimizing energy consumption and maximizing occupant comfort.
With sustainability continually gaining ground, the industry is at a critical moment to rethink how the materials we design and build with impact the triple bottom line. Traditionally, masonry has been perceived as a material used primarily for exterior claddings. It is time to change that school of thought. By relegating masonry to enclosures, the industry has overlooked obvious applications that have the capacity to further advance green building. Used in interior building design, masonry can reduce energy consumption, improve occupant comfort, decrease costs associated with materials, and make construction more efficient.
Sustainable Benefits to Holistic Masonry Design
When exterior masonry claddings are used in conjunction with masonry structural systems and exposed masonry surfaces in interiors, building efficiency is optimized. Masonry systems offer three major benefits over alternatives: they decrease the amount of continuous insulation required by code, reduce the risk of thermal bridging, and improve occupant comfort levels. Thermal mass materials like block, tile, and terrazzo absorb and retain heat. The International Energy Conservation Code (IECC) and ANSI/ASHRAE/IES Standard 90.1 — Energy Standard for Buildings Except Low-rise Residential Buildings require less insulation for mass walls than non-mass walls, like metal or wood frame. Therefore, masonry reduces insulation needs, saving money on materials for project owners.
How Passive and Active Design Strategies Work Together to Control Interior Comfort
Heating, ventilation and air conditioning (HVAC) systems are critical to managing interior building temperatures, but thermal mass can offset building owners’ reliance on active design components like HVAC, again helping to save money on energy expenditures. Thermal mass moves heat buildup away from the occupant and into the surface material, creating a change in air temperature surrounding the occupant and decreasing how hard HVAC systems must work to reach peak performance.
Using a combination of active and passive design strategies is key to delivering more sustainable and resilient buildings. Passive measures require a one-time, upfront investment, but the payoff extends throughout the lifespan of the building, improving comfort levels and lowering operating costs. Without passive measures, heating and cooling buildings becomes entirely dependent on the aid and price of operating HVAC systems.
Practical Design Tips: Optimizing Efficiency through Thermal Mass Material, Fenestration, and Façade Considerations
Thermal mass masonry materials are best used inboard of insulation. Block, tile, terrazzo, and other masonry materials are all available in a range of thicknesses to accommodate the appropriate amount of thermal mass for both vertical and horizontal surfaces. Consider using higher levels of thermal mass in functional areas that are not always occupied, but operate on the HVAC schedule throughout the day. This might include assembly rooms, gymnasiums, and circulation spaces.
To help meet cooling requirements, it is also important to utilize thermal mass in areas of the building that receive a greater level of solar gain. Even thin mass systems like tile can prove effective at absorbing heat, and should be considered a viable option, so long as it meets code requirements for mass walls. Additionally, wythe block walls work just as well for absorbing heat in interiors as they do for external walls. Regardless of the chosen material, it is important to keep in mind that thermal mass must be exposed to occupied space, in contrast to insulation, which is concealed behind finishes.
Thermal mass walls must also work in conjunction with fenestration. Though daylighting can reduce lighting demands, windows are poor insulators and can create undesired heat gain in building interiors. Make use of passive solar design techniques like proper orientation and massing of the building and locating and sizing of windows for the façade. Finally, always specify that windows balance daylighting with heat loss.
Keeping window-to-wall ratio (WWR) below 40% in all climates helps create energy efficient enclosures. ANSI/ASHRAE/IES Standard 90.1’s Prescriptive insulation tables found in energy codes stipulate that the maximum WWR is not to exceed 40%. In an analysis of buildings in various cities, the report “High Performance Based Design for the Building Enclosure” concluded that increasing WWR can actually offset savings made from daylighting, because of the poor performance of windows. Creating balance is necessary. Most schools and hospitals have WWRs of 20%-30%, a good rule of thumb to follow.
Though all-glass facades have taken hold as an aesthetic trend, their R-value – or capacity to resist heat flow – is so low that they are not practical when it comes to creating comfortable interior temperatures. Windows that extend down to floor level fail to provide daylighting deep into the interior of the building. Placing opaque walls in these locations is a better solution for offering higher R-values and minimizing negative impacts of daylighting. Opaque walls should extend upwards of thirty inches from the floor level for maximum energy efficiency.
In “Form and Skin: Antidotes to Transparency in High Rise Buildings,” renowned architect Ken Shuttleworth vouches for using opacity and insulation to design more sustainably: “The design of the tall building facade is at the forefront of a change. The fully glazed, totally transparent office block is dead, a thing from the past when regulations were more lenient and our attitude to the environment more naïve. The design of the tall building facade needs to incorporate more opacity, more solidity and more insulation, with windows strategically located where natural light penetration is actually required, as opposed to simply wrapping every inch of the building skin in glazing.” Nevertheless, all-glass facades have not disappeared. Energy codes will continue to change to help restrict designs that hamper energy efficiency. Designers, engineers, and builders must keep pace to meet shifting demands, and masonry can play a critical role in advancing the energy efficiency of structures.
The Impact of Continuous Insulation and Thermal Bridging on Energy Efficiency
Designers have a fair amount of flexibility when it comes to considering the energy performance of enclosures. For instance, ANSI/ASHRAE/IES Standard 90.1 provides prescriptive and mandatory enclosure requirements. Once they are met, however, designers can choose from three different enclosure compliance options to ensure overall building energy efficiency. Designers often opt for the least complex path – the Prescriptive Option – which includes requirements for continuous insulation. The simplest choice, however, is rarely the best in this scenario, as it does not prioritize optimization and efficiency. Though the Trade-Off and Energy Cost Budget Methods are more complex, they allow for greater design flexibility, making efficient overall energy performance more achievable. Sustainable building requires designers to think outside the box. Sometimes, it requires building owners to make a bigger investment upfront. As designers and builders, we must educate our clients on the long-term cost savings made possible by green practices.
Higher R-value (or lower U-factor) of continuous insulation does not always equate to improved overall building energy performance. R-value has a point of diminishing return, and cost-benefit analysis should be considered to weigh the best approach for any given project. Additionally, effective R-value can vary based on back-up wall construction and the degree of thermal bridging elements — either linear or point elements — that are a part of assembly. Cantilevered balconies, cladding support sub-framing, masonry veneer shelf angles, parapet walls, foundation transitions, and penetrating structural steel members are all examples of thermal bridging.
The traditional, two-dimensional, parallel approach to calculating the impact of thermal bridging on heat loss is to estimate the effective R-value. However, sophisticated energy modeling software and enhanced computing power has enabled researchers to more accurately assess the impacts of thermal bridging in recent years. In the 2011 report “Thermal Performance of Building Envelope Details for Mid- and High-Rise Buildings,” engineering firm Morrison Hershfield Limited found that thermal bridging has a much greater impact on the effective R-value than calculations have previously lead us to believe. That is because heat flows in all directions and extends beyond the boundaries of the bridge itself.
That said, thermal bridges do not always significantly impact the overall energy performance of buildings. The Building Envelope Thermal Bridging Guide, prepared by Morrison Hershfield Limited in collaboration with stakeholders and industry partners, offers an elegant and simple methodology to calculating the realistic impact of a thermal bridge, including a cost-benefit analysis to determine the payback period. That analysis can help reveal keys to optimizing energy performance. For instance, redesigning fenestration, parapet, and foundation interface details with thermal continuity could serve as an alternative to adding thermal breaks in cantilevered balconies or stand-offs to floor line masonry veneer shelf angles. On the other hand, if the analysis reveals that a shelf angle measurably impacts overall effective thermal performance, more in-depth engineering analysis following masonry codes could reveal that shelf angles are either not necessary, or can be reduced from what was dictated by the prescriptive design method.
As designers and builders continue to push towards sustainable interior solutions, masonry – which offers thermal mass, insulation compliance, and reduced thermal bridging – should be incorporated into practice to optimize efficiency and save money on energy consumption over the lifespan of a building.
The Sustainable Masonry Certification Program, (SMCP), offered by the International Masonry Institute (IMI), is an advanced educational program that provides union masonry contractors intensive training in the U.S. Green Building Council’s (USGBC) LEED program. SMCP was created in 2009 and earned the distinction of being the first sustainable construction training program approved by USGBC. Training focuses on masonry as a sustainable building system and addresses subcontractor LEED compliance responsibilities from estimating to documentation. SMCP covers all masonry trades: brick, tile, stone, terrazzo, cement, plaster, and restoration. Since its launch, IMI has educated hundreds of masonry contractors, project managers, and estimators across the U.S. and Canada. To enquire about SMCP enrollment, visit http://imiweb.org/4-contact.
About the International Masonry Institute (IMI)
The International Masonry Institute (IMI) is a strategic alliance between the International Union of Bricklayers and Allied Craftworkers and the contractors who employ those members. Through education, technical support, research, and training IMI works to provide a more efficient construction delivery system.
Building Envelope Thermal Bridging Guide 1.1. 2016: Morrison Hershfield Limited.
Shuttleworth, Ken. “Form and Skin: Antidotes to Transparency in High Rise Buildings.” Council on Tall Buildings and Urban Habitat, 2008.
Standard 90.1-2016 — Energy Standard for Buildings Except Low-Rise Residential Buildings. ANSI/ASHRAE/IES, 2016.
Thermal Performance of Building Envelope Details for Mid- and High-Rise Buildings (1365-RP). Rep. no. 5085243.01. 2011: ASHRAE.
Jeff Diqui has a Bachelor of Science Degree in Architectural Engineering with a major in Structural Engineering from Milwaukee School of Engineering. He has over 25 years of experience focused on the building enclosure. His career has included work in forensic investigations related to moisture intrusion and structural-related problems, structural design, building condition assessments, development of repair / rehabilitation designs, and construction observations.
Brian Trimble has an Architectural Engineering degree from Penn State University and is a Licensed Professional Engineer in Pennsylvania and Virginia. He has over 25 years’ experience in the masonry industry, with a focus on assisting design professionals with masonry structures.
Maria Viteri, AIA, LEED AP BD+C
Maria Viteri is a registered architect in Pennsylvania who explores the role of masonry in advancing a building’s sustainable and energy goals. Maria practiced in Pittsburgh and is experienced in architectural design and construction administration. She holds a Bachelor/ Master of Architecture from Tulane University and a dual M.B.A./Master of Public and International Affairs from the University of Pittsburgh.