Article No: 243

2008-09-29 10:23:28
Concrete Makes it Easier For Builders to Meet the California Green Building Standards Code
By: Donn C. Thompson AIA, CGP, LEED AP


 
The State of California is again pursuing improvements in environmental policy, this time directly impacting all types of new construction within the state. New green building provisions, titled the “California Green Building Standards Code” (CGBC), are intended to reduce greenhouse gas emissions, improve energy efficiency, and conserve water in all structures. Concrete homebuilding systems offer unsurpassed energy efficiency, reduced air infiltration, and recycled content benefits, which will enable these technologies to provide an attractive means of meeting the residential provisions of the new California code.  

The California Building Standards Commission adopted these provisions on July 17, 2008. It is the first time a state has mandated green building requirements covering all new construction, public or private, commercial, as well as residential. Responsibility of building codes in California is split among several agencies, each of which has specific control of one or more occupancy types. Each agency identified specific environmentally sensitive construction requirements for building uses within their jurisdiction. There are very stringent requirements for all types of publicly funded construction and more limited requirements for privately funded home building projects.  

The Department of Housing and Community Development (HCD) regulates the building of low rise single and multi-family housing. HCD has identified six different categories, each with specific green building measures that must be complied with to meet the code, (Table 1).  Home builders can voluntarily incorporate these provisions in houses built now, but after 2010, compliance will likely become mandatory when the next edition of the California Building Code is to be finalized and adopted. Home builders should also be aware that each county and city building department will be allowed to make their own changes to the CGBC to meet specific local conditions.

Concrete systems will contribute to conformance within three of the HCD identified categories: Energy Efficiency, Air Sealing Package, and Material Conservation and Resource Efficiency. The code directly references traditional construction methods but alternative materials, designs, and methods not specifically described in the code can be used as well. However, alternative materials and local changes must be submitted for approval by the HCD.
 

 
Energy Efficiency
Low-rise residential buildings will have to meet the minimum requirements of the California Energy Standards in effect when the code is adopted. State energy requirements for conforming homes currently exceed the minimum requirements of the 2006 International Energy and Conservation Code (2006 IECC). Future requirements may become more stringent.

Concrete walls can provide high insulation levels, reduction of air infiltration, and important thermal mass benefits. Thick layers of insulation are typically an important component of exterior concrete walls, with possible steady state R-values well in excess of the minimum amount of insulation currently required in California. The higher the R-value, the better insulated the wall. 

When built with concrete systems, outside walls will have more solid, more continuous layers of structure and insulation than with stick built systems. There are fewer pathways for outside unconditioned air to find its way into a home. With less outside air infiltrating into the structure, there is less load imposed on mechanical equipment. 

Adding the thermal mass benefit further boosts the superior energy performance possible with concrete systems.Concrete wall assemblies will absorb heat energy from the surroundings and store that energy until the air temperature around the walls drops. The walls can then slowly release the heat back to the surroundings. This serves to create a delay in the impact temperature extremes will have on the interior spaces, further reducing heating and cooling loads and fossil fuel consumption. By saving energy, concrete wall systems reduce the amount of greenhouse gas emissions a home will produce. Careful life cycle analysis has demonstrated the energy efficiency benefits of one concrete house built in a hot, dry climate will reduce greenhouse gases by 441,000 lbs over its anticipated 100 year life span when compared to a wood framed1 home. Additional reductions in other emissions associated with ozone depletion, acid rain, harmful stormwater runoff, and smog are also realized.   

Concrete homebuilding systems have been used successfully as an important component of carefully designed whole-house energy performance strategies to meet or exceed energy code requirements across the US. As local requirements increase, contractors will need to perform additional work and coordination to make frame walls qualify, while the higher quality and performance of concrete systems will continue to enable builders to more easily achieve these requirements.

Air Sealing Package
All joints in exterior walls will need to be properly sealed. With all of the “parts and pieces” of frame, many seams and joints exist, creating time consuming and costly quality control issues for the builder. The California Green Building Standard Code identifies five different areas in frame walls that must be sealed. Four of these areas would be eliminated with continuous concrete.  Only attention to joints around windows, doors, and utility penetrations would still be required.  Concrete wall systems, with far fewer joints and little coordination requirements, simplify conformance for the builder.

Material Conservation and Resource Efficiency
Under this green building measure, a minimum of 50% of the construction waste generated at the site is required to be recycled or salvaged. When placed on site, concrete generates little waste. Any leftover material can be crushed and reused as backfill, or base material beneath pavement. Panelized precast and modular concrete systems can be installed with virtually no waste on site. By using concrete systems for the exterior walls, contractors will have far fewer material handling issues than with frame construction. 

The California green building provisions for low rise residential construction outlined above, are far more limited in scope than those established under the US Green Building Council’s LEED for Homes system or the National Association of Homebuilders’ Model Green Home Building Guidelines and National Green Building Standard. State-owned residential construction will be required to meet broader, more stringent standards similar to the national residential green building programs. For these green projects, concrete homebuilding systems continue to offer numerous additional benefits including contaminated site reclamation, added durability, mold resistance, high solar reflectance, recycled content, erosion control, pervious and permeable pavements, and improved indoor air quality.  

The California Green Building Standards Code represents a first attempt at mandated statewide green construction requirements and furthers the growing awareness of sustainability in residential design. In California, and nationwide, concrete offers an unbeatable combination of disaster resistance, energy efficiency, long lasting value, and perpetual recycling to achieve compliance with the various programs and standards for more environmentally sensitive homes.
1 “Life Cycle Assessment of an Insulating Concrete Form House and a Wood Frame House” by CTL Group for Portland Cement Association, 2008 Serial No. 3041

More information including a complete copy of the 2007 CGBC including the Application Checklist developed by the California Department of Housing and Community Development for low-rise residential construction is available at the California Building Standards Commission web site bsc.ca.gov/prpsd_stds/default.htm

More information on Concrete Homebuilding Systems can be found at the Portland Cement Association residential web site, concretehomes.com

Donn Thompson, dthompson@cement.org, is Program Manager for Residential Technology of the Portland Cement Association