As owners and developers become more energy and environmentally conscious, design teams are required to carefully implement sustainable design principles. The building's structure has a significant impact on the building's embodied energy and the ability to achieve LEED points.

Embodied energy is defined as the available energy used in the work of constructing a building. A building's structure accounts for about 25% of the building's embodied energy but only about 10% of the building's cost. A knowledgeable LEED AP structural engineer on your project can assist with sound sustainable design principles that can significantly reduce the building's embodied energy.

The four most common structural materials are concrete, masonry, steel, and wood. Each material has a unique set of attributes and properties. Structural engineers should be careful when specifying the structural components of a building in order to capture all of the available LEED points and minimize the building's embodied energy. Here are a few ways the structural engineer can help achieve LEED points.

Concrete

  • Credit MR 1. Existing concrete buildings often can be reinforced and reused.
  • Credit MR 2. Concrete can be crushed and reused as fill material. Steel rebar can be recycled.
  • Credit MR 4.1 and MR 4.2. Rebar is made with recycled steel. Cement increases CO2 emissions. Pozzolans, such as fly ash (used in high-volume fly ash concrete or HVFA) and ground granulated blast furnace slag can reduce cement content more than 50%.
  • Credit MR 5. Locally manufactured and extracted materials commonly are available.

Masonry

  • Sustainable Sites Credit 6 and 7 (SS 6 and SS 7). Permeable concrete, masonry pavements, or open-cell concrete masonry pavers can improve stormwater management and reduce nonroof heat island effects.
  • Credit MR 1. Existing masonry buildings often can be reinforced and reused.
  • Credit MR 2. Masonry can be crushed and reused as fill material. Steel rebar can be recycled.
  • Credit MR 4.1 and MR 4.2. Rebar is made with recycled steel. Concrete masonry units and grout can be made with HVFA. Clay brick often is made with recycled brick ground and used as grog, which can qualify as post-consumer recycled content. Other common recycled content in masonry is bottom ash, fly ash, sludge, and even contaminated soil.
  • Credit MR 5. Locally manufactured and extracted materials commonly are available.

Steel

  • Materials and Resources Credit 1 (MR 1). Existing steel frame structures easily can be reinforced so the original structure can be reused.
  • Credit MR 2 and MR 3. Steel is the most recycled material in the world. Virtually any steel on a construction site can be recycled or refabricated and reused.
  • Credit MR 4.1 and MR 4.2. Most structural steel shapes are made from 97% recycled material. Recycled content in steel plate is about 65%. HSS sections typically are not made with recycled steel and should be avoided on LEED projects. The Steel Recycling Institute, Pittsburgh, reports that the post-consumer recycled content is about 64% and the post-industrial recycled content is about 30%.
  • Credit MR 5. Steel usually is manufactured locally, but locally extracted materials are not always available.

Wood

  • Credit MR 2. Wood is easily recyclable and reused.
  • Credit MR 5. Locally manufactured and extracted materials can be available for some projects.
  • Credit MR 6. Wood is an entirely renewable material.
  • Credit MR 7. Sustainable material suppliers with FSC-certified wood products are readily available.
  • Indoor Environmental Quality Credit 4 (EQ 4). Specify adhesives used in composite wood, engineered lumber, and agrifiber to comply with South Coast Rule #1168 and Green Seal GS-36. Also specify the material to not contain added urea-formaldehyde resins.

A building's structure has a significant impact on the building's embodied energy and its ability to achieve LEED points. An astute LEED AP structural engineer is a valuable design team member and can help implement sustainable design principles.

Chris Hofheins is a principal for BHB Consulting Engineers, Salt Lake City.