OVERVIEW OF THE LEED FOR COMMERCIAL BUILDINGS RATING SYSTEM
LEED is a rating system developed by the United States Green Building Council. The rating system outlines important sustainable design features that commercial buildings should incorporate, and provides a scoring system to rank success. The rating system is available on the USGBC website: www.usgbc.org/Leed/Rating-systems. LEED does a good job of outlining the important aspects of green design applied to commercial buildings. Where a building is located is an important con sideration. How a building uses water and how much water it uses will become more important as population increases. Minimizing energy use is obviously a primary concern. Material choices must balance embodied energy, recycle content, and durability. And finally, indoor environmental quality is very important to the people who occupy a building. LEED creates a list of features under the headings mentioned above. Each of the items in the list has points related to it. The total points earned by a design grades the design as certified, silver, gold, or platinum. This grading system is not perfect but it does create a clear definition of green. The discussion below is based on the LEED 2009 rating system. The LEED green rating system is adjusted every few years but the basic structure stays stable.
The site selection category aims site selection away from sensitive locations like wetlands, undeveloped land, farmland, and critical habitat areas. Maximizing open space on the site is given importance. There is also credit given to locating the building on a brownfield site. All of these considerations restate the old adage to site a building on the worst piece of land in order to improve the environment of the site. The next group of criteria relate to where the building is located in an urban setting. A building that is located close to services like banks, cleaners, libraries, theaters, supermarkets, and so on, and also reasonably close to housing opportunities will create more walking and less driving. A building’s location can also reduce driving by creating opportunities to use public transportation, and can design features to promote bicycle use, carpooling, and the use of low emitting vehicles. Storm water design features are encouraged that reduce the amount of runoff by minimizing impervious ground cover (paved areas), and by filtering the runoff that does occur through constructed wetlands. Urban areas are warmer than unbuilt areas because of massive areas of paving and dark roofs. Replacing paving with green areas and shade trees and replacing dark traditional roof coverings with white surfaces and green roofs can mitigate the heat island effect. The final site feature addressed is light pollution caused by street and building lighting. The stars are barely visible in the night sky over a city when compared to the night sky in open, undeveloped country.
Water is used in buildings for drinking, washing, and waste removal. The washing and waste removal streams can be minimized with low flow fixtures. The waste removal stream could use non-potable water sources like rain water. The waste stream could be eliminated with composting toilets or by treating waste water on site and then reusing it to operate the waste stream. Building sites can be designed to minimize or eliminate the need to irrigate planting by using local plantings that can survive on the local rainfall and or collecting rain water to use for irrigation.
The primary focus of the energy and atmosphere category of the code is minimizing the energy use of the building. The base line is 10 percent better than ASHRAE 90.1–2007. Most of the available points are for reducing energy use below the baseline. There are requirements for building commissioning to confirm that the mechanical and electrical equipment is installed correctly and that the owner has documented knowledge of how to operate the equipment. Consideration is also directed to on site renewable energy generation as well as purchasing green energy through the utility company. Finally there are points for a measurement and verification system to confirm that the energy use predictions from the design are achieved in the actual building.
The materials category is set up to reward material reuse and recycling. At the building level, the structure of the walls, floors, and roof can be saved, and in addition nonstructural interior construction elements can be saved. At the materials level credit is given for reusing materials, for materials with recycled content, for regional materials, for rapidly renewable materials, and for the use of certified wood.
Indoor environmental quality covers air quality, lighting and daylighting, and thermal comfort. Air quality is addressed on two fronts. Increased ventilation will dilute any volatile organic components in the air, and low emitting materials for adhesives, sealants, coatings, paints, flooring, and composite wood products reduce the amount of volatile organic components in the air. Lighting is required to be controllable, and daylighting and views to the exterior are encouraged. Thermal comfort also needs to be controllable and verifiable.
Using design features that are innovative and not considered by the point structure of the LEED system is viable and can earn credits. In addition, one credit is given for using a LEED accredited professional to guide the process.
Regional LEED organizations can define some of the LEED criteria as very important in the local environment. Bonus points are then given for the implementation of those criteria.