IMI offers a variety of resources on the topic at no cost to designers and builders, including guides, manuals and a series of informative webinars and in-person training.


Recent studies tie a building’s energy performance with the quality, construction, and performance of the building envelope. In addition to protecting its occupants from the elements, energy usage can be curbed by maximizing building envelope performance. Energy efficiencies are further achieved by implementing passive design measures on interior surfaces.

Masonry’s greatest sustainability benefits are reached by looking beyond the material as a finish and instead matching masonry systems to the building’s functional needs and sustainable outcomes. Masonry systems, with the ability to enhance a building’s thermal performance, provide one of the best passive design options and result in an integrated passive design strategy that balances building performance with heating and air conditioning requirements. Passive measures are paid for once, yet perform repeatedly over the life of the building.

Building Envelope Performance is based on:
  • Thermal Resistance
  • Thermal Mass
  • Airtightness
  • Moisture Tolerance
  • Sustainable Details and Materials

Building practices related to energy performance are directed by energy codes and improved upon by desired performance levels. Energy codes set minimum performance standards. Building function, occupancy and classification often directs the design team to improve upon these minimum performance standards.


So where do we begin?  

Designers refer to Section 5 of ASHRAE 90.1 for building envelope requirements. Listed by climate zone, building envelope requirements are defined as opaque elements: roofs, walls, and floors, and fenestration: windows and skylights. For the building envelope, one of the key measurements related to managing thermal loss and is measured as the R-value  for insulation in the building wall, or Assembly Max U-Factor  for the full wall assembly.   One of the key overlooked options for compliance with ASHRAE 90.1 is the option to either meet requirements for R-value or U-factor. For reasons related to constructability and energy modeling, IMI strongly suggests that designers look at the value of U-Factor measurement as well as R-value compliance to fully understand where the designed building envelope stands as far as meeting and superseding energy requirements.


Masonry benefits for energy design

Masonry’s major benefit to energy design is its thermal mass characteristics. Masonry’s ability to absorb and store heat energy serves to slow down the transfer of heat. This characteristic makes masonry valuable as a compliment for heating and cooling expand as to why

Thermal Mass works in conjunction with insulation and reduces thermal transfer through conduction and heat absorption characteristics. ASHRAE 90.1 recognizes this and therefore requires less insulation in a thermal mass solution versus a stud wall solution.

  • Thermal mass materials absorb excess internal heat loads created by people, lights, and equipment and reduce peak loads that result in higher energy usage.
  • Thermal mass contributes to a building’s higher level of energy performance with a lower level of HVAC operation.
  • ASHRAE 90.1 recognizes mass construction and reduces insulation requirements on mass walls.
  • ASHRAE 90.1 Prescriptive tables provide information for insulation R-Value and also assembly U-Factor.
  • Designers should incorporate all of the benefits of the assembly and design for a minimum U-Factor.
  • To address energy and operating costs, consider using brick, block, stone on exterior envelope and interior horizontal walls as well as tile and terrazzo for interior surfaces.

Confirm no more than 40% fenestration. Match project location to climate zone.

  1. Section 5, Building Envelope provides R-value and U-Factor tables per climate zone
  2. Refer to requirement for Opaque elements, Walls Above-Grade; Masonry = “MASS”
  3. Remember R-Value is INSULATION only
  4. U-Factor listed refers to assembly
  5. Gather your full assembly R-value (all materials and air films)
  6. Convert your full assembly R-value using formula U factor = 1/R-value

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 the IMI works to provide a more efficient construction delivery system.