Potential Point Contributions to LEED Certification for Structures Using Precast Concrete
5.1: Site Development — Protect or restore habitat.
A precast concrete building design can help limit site disturbance to prescribed distances from the building. Less dust and waste are created because only needed precast concrete elements are delivered. Fewer trucks and less time are needed because concrete is made off-site. This is particularly beneficial in urban areas. Precast concrete units are normally large components, so greater portions of the building are completed with each activity, creating less disruption and noise. Concrete buildings can be designed with tuck under parking. This reduces the amount of land needed for parking lots and increases the amount that can be left as natural areas.
7.1: Heat Island Effect — Non-roof.
The requirement is met by placing a minimum of 50% of parking spaces under cover (defined as under ground, under deck, under roof, or under a building and having a Solar Reflectance Index (SRI) greater than .3). This is easily achieved through mixed-use precast structures with parking under or free standing parking structures. Concrete typically has SRI between 0.35 and 0.8. Asphalt typically has reflectance less than 0.3 and does not meet the criteria. Thermal Images taken with digital infrared thermometer showed an average 40 degree temperature difference between new concrete and new asphalt. The Portland Cement Association conducted an extensive study on the SRI of concrete and a free report is available. http://www.cement.org/bookstore/profile.asp?itemid=SN2982
7.2: Heat Island Effect—Roof.
Mixed use structures with concrete parking over or green roofs on precast structures can be considered.
8.0: Light Pollution Reduction—Minimize site lighting where possible
Structured precast parking will require fewer fixtures to produce the same level of lighting compared to asphalt parking lots. Other benefits are reduced light trespass from the building, improve night sky access, reduce development impact on nocturnal environments and reduced energy demand.
30% fewer fixtures can produce the same level of lighting on concrete vs asphalt.
Required Minimum Energy Performance—Establish the minimum level of energy efficiency for the proposed building and systems. Precast concrete’s thermal mass and insulated sandwich wall panels help increase energy efficiency.
Optimize Energy Performance — Achieve increasing levels of energy performance above the baseline in the prerequisite standard to reduce environmental and economic impacts associated with excessive energy use.
Field tests and analytical studies demonstrate that for most climates, buildings constructed with concrete use less energy for heating and cooling compared to buildings constructed with lighter weight materials.
The inherent energy efficiency of concrete construction derives from concrete’s thermal mass properties. Concrete acts like a heat “sponge,” which absorbs heat energy and thus moderates indoor temperatures and peak heating and cooling loads. As a result, the peak heating and cooling demand and annual energy performance of high mass buildings are often reduced. In addition, the HVAC system capacity of an efficient, high mass building may be less than a lighter building of the same size. While building mass reduces energy consumption in nearly all North American climate zones, it is most effective in areas and during seasons that see large daily temperature swings. Precast concrete’s thermal mass and insulated sandwich wall panels help increase energy efficiency.
2.1: Construction Waste Management—Divert 50% by weight or volume.
Because the LEED Construction Waste Management credit does not recognize upstream waste reduction, precast does not contribute to this LEED credit. Precast does however, result in considerably less construction site waste since it is shipped unwrapped, with very little cushioning. Conventional built-up construction includes a range of products that are packaged, wrapped, or cushioned with materials that are sometimes not recyclable. Because precast concrete is not typically cut on the jobsite, cut-off waste is also dramatically reduced.
2.2: Construction Waste Management—Divert 75% by weight or volume.
Same as above.
4.1: Recycled Content—The post-consumer recycled content plus one-half of the pre-consumer content constitutes at least 10% (based on cost) of the total value of the project's materials.
Fly ash, slag cement, and silica fume are industrial by-products called supplementary cementitious materials (SCMs) and are used as a partial replacement for portland cement in precast concrete products. SCMs do not contribute to the energy and CO2 impacts of cement in concrete. These are pre-consumer materials and if not used in concrete would be sent to landfills. Fly ash is a by-product of the combustion of pulverized coal in electric power generating plants. Slag cement, also called ground granulated blast furnace slag, is made from iron blast-furnace slag. Silica fume is a by-product from the electric arc furnace used in the production of silicon or ferrosilicon alloy.
Standards reference are ASTM C618 for fly ash, ASTM C989 for blast furnace slag, and ASTM C1240 for silica fume. Fly ash is commonly used at replacement levels up to 20%; slag cement up to 25%; and silica fume up to 10%. Exact dose will vary based upon products and a local precast manufacturer should be consulted prior to setting project goals.
Other recycled materials included in precast concrete are insulation, steel reinforcement and connection hardware.
4.2 Recycled Content—An additional credit is available if the project uses 20% post-consumer recycled content.
Same as above.
5.1 Local/Regional Materials—Use a minimum of 10% (based on cost) of the total materials value.
Most precast concrete components use local material (sand, water, aggregates) and are made at a plant close to the site, saving transportation costs.
Precast concrete components are usually transported and erected within 200 miles of the plant, easily meeting the 500-mile LEED requirement. Most precast concrete products are manufactured with materials extracted, harvested, or recovered within 500 miles, such as aggregates, cement, sand, reinforcing steel, and additives.
5.2 Local/Regional Materials—Use a minimum of 20% (based on cost) of the total materials value.
Same as above.
3.1 Construction Indoor Air Quality - Construction Indoor Air Quality Management Plan, During Construction
Strategies: Maximize the use of precast to avoid creating onsite airborne contaminants during construction.
- Strategies: Maximize the use of precast to avoid creating onsite airborne contaminants during construction.
- Precast has very low off gassing and is sound-proof and fire resistant.
- Consider installing windows at precast plant.
- Because precast concrete is inert, it does not require VOC-based preservatives.
- Textured interior walls can provide aesthetic alternatives to paints or wall board.
- Use pigments for color instead of painted surfaces can also be considered.
1.1–1.5 Innovation Credits—Apply for other credits demonstrating exceptional performance (must be submitted and approved).
Precaster can help create innovative systems that achieve key sustainability goals. material and transportation costs).
2.1 LEED Accredited Professional.
Some precasters have LEED Accredited Professionals on staff to aid with the design process.