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When constructing a green home, builders and developers have the choice of following a broad array of programs, rating systems, and laws. This breadth of options often causes some confusion over the precise definition of a green home. Is a green home a home that is constructed solely from local materials? A home that uses substantially less energy than the average home or is net-zero energy or carbon neutral? A home that recycles wastewater? A home built with non-toxic and non-VOC off-gassing materials? Or all of the above?
It is not sufficient to create a home that is simply green. Beyond Green™, the tagline adopted by the Sustainable Buildings Industry Council in 2006, helps convey the commitment to designing and building high-performance homes.
To go Beyond Green™, homebuilders should apply an intentional integrated approach to design and a strong integrated team process. The eight design objectives which are all, to some greater or lesser degree, important to any project, are integral components of that process and are outlined below for consideration in the residential design process. A true green home acknowledges the importance of all building elements, from designing an air-tight, well-insulated wall system to choosing high-quality windows.
This document is not intended to replace the standards, codes, and other guidance available from numerous other sources, but to provide an introduction to key concepts and considerations essential for producing high-performance homes. The reader is encouraged to consult additional resources for in-depth guidance, and references are provided throughout this document. Homebuilders must also work with their clients and subcontractors to determine the levels of performance desired.
Whole Building Design Approach for Residential Design
The Whole Building Design Approach encourages integration and optimization among all building measures. It is important to note that many green building programs also help foster this balance by requiring mandatory attention to all principles, not just one area. These concepts serve as the underlying basis for the Whole Building Design Guide which is discussed in more detail below.
Builders interested in using the whole building approach will consider the following eight design objectives in order to create a high-performance home: accessibility, aesthetics, cost effectiveness, functionality, productivity and health, history, safety/security, and sustainability. Unlike the more traditional approach in which design decisions are made one after the other, the whole building approach relies on careful consideration and integration of all key design objectives during every phase of the project.
This approach works particularly well when applied to a single home or larger, more complex, mixed-use developments. Although it may not be obvious at first glance, green strategies such as conserving energy and water, selecting the right materials, focusing on durability, or ensuring great acoustical comfort, all affect which other attributes are incorporated and how successful they will be.
Some groups who previously concentrated on just one of these attributes have added green elements to their programs. For instance, many advocates for affordable housing have decided to go green because homes that save energy free up money for other living expenses.1
The eight design objectives that contribute to building a high-performance residential building are as follows.
This design objective considers accommodating persons who are permanently disabled or temporarily disabled due to an injury. The concepts of visitability and aging in place are becoming more popular as the percentage of our aging population grows. The visitability movement advocates for constructed homes to consider aspects such as the location of stairs and the width of interior doors. The goal is to ensure equal use of the home for all.
What qualifies as beautiful is open to personal interpretation and varies with client, climate, context, construction and culture. Aesthetics applies not just to the outside architecture, but to the interior design, the surrounding landscape, the neighboring buildings and the community at large.
There is no one specific measure for true cost effectiveness, but some considerations are noted here. Does the homeowner want the lowest first cost or the lowest operations and maintenance (O&M) costs? Is it the home with the longest life span? Will the house be used for a combination of purposes, such as a home office? If so, it must accommodate the public.
Understanding how the home will fit its owners means defining the size and proximity of the different spaces needed for activities and equipment. Consider the owners' future needs, such as potential spatial changes from remodeling, and provide proper clearances for replacing or expanding building systems and equipment. Anticipate changing information technology (IT) and other building systems equipment.
Productivity and Health
The indoor environment of the home can have a strong effect on occupant health and the productivity of occupants, particularly young children and the aged, whose auto-immune systems are more susceptible to toxic materials and off-gassing fumes. Excessive noise, glare, drafts, heat, humidity or cold can be potentially damaging or dangerous. Builders must design the building enclosure, building systems, equipment, and appliances to work together as a unified system to achieve a truly healthy home.
Some practical and/or intangible benefits of historic preservation include: retaining history and authenticity; commemorating the past; increasing commercial value when homes feature materials and ornaments that are not affordable or readily available any longer; and reducing the need for new materials.
Safety and Security
Designing and constructing safe, secure homes and communities is a primary goal. Builders must consider different issues, such as improved indoor air quality, electrical safety, ergonomics, and accident prevention. Resisting natural hazards requires protection from hurricanes, wildfires, floods, earthquakes, tornados and blizzards. Gated and/or guarded communities are becoming more and more popular and may often require special maintenance and equipment.
The construction, use, and demolition of homes have many direct impacts on the environment. To ensure the sustainability of a home, consider the following principles:
Optimizing Site Potential. This principle covers such aspects as proper site selection, consideration of any existing buildings or infrastructure, orientation of streets and homes for passive and active solar features, location of access roads, parking, potential hazards, and any high-priority resources that should be conserved such as, trees, waterways, snags, and animal habitats.
Minimizing Energy Use and Use Renewable Energy Strategies. This principle covers aspects such as the importance of dramatically reducing the overall energy loads (through insulation, efficient equipment and lighting, and careful detailing of the entire enclosure), limiting the amount of fossil fuels required, incorporating renewable energy systems such as photovoltaics, geothermal heat pumps, and solar water heating whenever feasible, and purchasing green power in order to minimize the creation of greenhouse gasses.
Conserving and Protecting Water. This principle covers aspects such as reducing, controlling or treating site runoff; designing and constructing the home to conserve water used inside and outside; and minimizing leaks by ensuring proper inspections during construction.
Using Environmentally Preferable Products. This principle covers such aspects as specifying products that are salvaged, made with recycled content, are easily disassembled for reuse or recycling, conserve natural resources, reduce overall material use, are exceptionally durable or low maintenance, naturally or minimally processed, save energy and/or water, and/or reduce pollution or waste from operations.
Enhance Indoor Environmental Quality. This principle covers strategies to provide excellent acoustical, thermal, and visual qualities which have a significant impact on health, comfort, and productivity. Other attributes to be considered: maximize daylight, appropriate ventilation, and moisture control, and the use of low- or no-VOC products.
Optimizing Operations and Maintenance Practices. This principle covers materials and systems that simplify and reduce operational requirements, require less water, energy, and toxic chemicals and cleaners to maintain, are cost-effective and reduce life-cycle costs.
Flexible Design. Also called "loose fit, long life," this design principle anticipates and allows for future adaptations needed to extend a building's useful life.
Design for End of Life. This principle encourages design for the disassembly, reuse, and/or recycling of building components and materials at the end of their useful life.
When to Apply Green Strategies
It is very important that each green building strategy be applied at the appropriate stage to avoid closing off options. For example, not much can be done to affect the orientation of the house after the framing is underway, but much can be done during the design of the home, and even more during the layout of roads and lots. Table 1 gives a rough guide on when to consider major design issues, systems, and components.
Table 1: Stages for Applying Green Building Strategies
|Stage||Issues to Consider|
|Land Planning||Solar access
Saving natural plants and areas
Community stormwater management
Buffers from adjacent development
Traditional neighborhood development
|Site Planning||Wind buffers
Porches and decks
Reduced site paving
Grading and site water management
Landscape and shading
Acoustical and visual buffers
|Basic space layout relative to sun, wind, views
Septic systems and wells
Utility service entries
Auto and pedestrian access
|Construction Process Planning||Construction waste management and
Hazardous waste disposal
|Reduced site disturbance
Site construction access & storage
Storage and reuse of on-site excavation and soils
|Basic Design||Glazing and solar access
Provisions for efficient and energy saving duct layout
Mechanical equipment inside the conditioned envelope
|Design for recycling by homeowners
Avoiding attached garage if possible
Avoiding excessive size
Incorporate natural lighting wherever possible
|Specifications||Evaluate materials including:
Cladding and roofing
Air-sealing materials and systems
Cabinetwork and accessories
Plumbing and water heating
Mechanical equipment selection
Electrical and lighting
|During Construction||Changes that do not affect other
elements and do not increase energy
consumption or otherwise compromise
green building objectives
|Photograph and record work that will be hidden|
|Post Construction||Commission to ensure proper operation
of green building elements and systems
|Home Energy Rating/Energy Star approval
Home buyer education and operating manual
Avenues to Develop High-Performance Residential Buildings
Building Codes and Standards
Building codes establish minimum requirements for building design and construction. These codes are designed to improve the quality of building construction and ensure that new projects achieve certain health and safety standards.2 Building codes protect people and the buildings they inhabit from potentially harmful events such as structural failure, fire, earthquakes, and hurricanes.
Organizations such as ASHRAE continually develop and modify standards to be released at the national level. States and local legislative bodies may adopt the latest version and customize the code to reflect local building practices and regional conditions. While these codes are developed for wide-scale adoption, it falls upon the states and local municipalities to adopt, implement, and enforce code requirements.
All building types are not subject to the same codes. For example, the International Code Council (ICC) has released 14 different codes, dubbed the I-Codes or the International Family of Codes. I-Codes address a range of topics including fire safety, energy-efficiency, and green construction, to name a few. Energy and green construction codes are gaining more prominence as the building industry moves in the direction of sustainable, energy-efficient, high performance buildings.
Codes and Standards for Energy Efficiency
A subset of building codes are building energy codes, which establish minimum requirements for energy efficiency in buildings.3 These regulations indicate how a building should be designed and built to achieve desired levels of performance. Early attempts to push the adoption of improved energy building codes began with the Energy Policy & Conservation Act (EPCA) of 1978. The EPCA dictated that states receiving federal funding had to initiate energy conservation standards for new buildings. In 1992, the Energy Policy Act was created to address energy conservation, efficiency, and management. The Energy Conservation and Production Act dictates that each state must have commercial building codes that minimally meet ANSI/ASHRAE/IESNA Standard 90.1 (ASHRAE 90.1). Energy codes encourage the development of high-performance buildings through greater efficiencies that reduce utility bills and enable buildings to have smaller, less expensive HVAC equipment. Energy codes address several efficiency measures, from insulation requirements for ductwork and piping, to lighting controls, to minimum mechanical equipment efficiencies. Energy codes can be classified as either minimum (baseline) or reach (above/beyond/stretch) codes. Minimum codes set the floor of building code standards, while reach codes raise the ceiling, pushing high-performance buildings closer and closer to net-zero energy use.
Minimum and Reach Codes
Minimum codes establish baseline requirements for buildings and are mandatory regulations. States and local jurisdictions may adopt and alter the code, provided that they are at least as stringent as required by federal mandate. The International Energy Conservation Code (IECC) and ASHRAE 90.1 are minimum energy codes/standards that are updated every three years. Designers, developers, and contractors are responsible for complying with code. States or local jurisdictions are responsible for enforcement through plan reviews and construction inspections.
The rapid development of reach codes (also known as stretch codes) aim to create consistent requirements for higher-performing buildings. Normally voluntary, reach codes encourage the creation of higher-performing buildings by pushing for buildings that are more sustainable, addressing a range of topics like energy and water efficiency, site and material selection, indoor environmental quality, and project management. Many jurisdictions have adopted a reach code, requiring new buildings to meet more stringent requirements than versions of the IECC or ASHRAE 90.1. Reach codes can influence model code development with aspects of reach codes being incorporated into model codes over time. There are over 300 reach codes or green building programs used throughout the United States. The following charts describe the model codes and some reach codes.
Sometimes likened to a push/pull approach—with mandatory requirements acting as a pushing force and incentives seen as a pulling force—many policymakers, utilities and concerned citizens see codes ultimately leading to achievement of net-zero energy buildings (NZEB). While a formal definition has not been codified, the name implies that annual output of renewable energy produced onsite is equal to the annual purchased energy from a utility. Energy efficiency measures, smart design, and renewable energy strategies can all contribute to a net-zero energy building.
Besides the obvious environmental advantages, a NZEB can protect occupants from energy price increases and future regulations; provide increased comfort (by establishing a uniform interior temperature); reduce total cost of ownership; improve reliability; and support higher resale values.
Certain market disadvantages do currently exist, including: high upfront costs, reliance on renewable energy subsidies (which can be uncertain) and building appraisals that do not consider long-term energy considerations.
Table 2: Example Building Energy Model/Baseline Codes
|ANSI/ASHRAE/IES 90.1 Energy Standard for Buildings Except Low-Rise Residential Buildings||Commercial/ High-Rise, Multi-Family Residential (above 3 stories tall)||Updated every 3 years. States/local jurisdictions modify to reflect regional building practices or state-specific energy efficiency goals.|
|International Energy Conservation Code (IECC)||Commercial/Residential||Updated every 3 years. One of 14 model codes ICC creates. States/ local jurisdictions alter to reflect regional building practices or state-specific energy efficiency goals. Contains alternative compliance path of ASHRAE 90.1.|
|International Residential Code (IRC)||Residential||Energy related provisions mirror those contained within the IECC.|
|CALGREEN Green Building Standards||Commercial||California's mandatory green code. New York, Florida, and Oregon also have own codes.|
There are a number of green building programs currently in place in the United States. Some of the many above/beyond/reach/stretch codes or green building programs are described in the following chart:
Table 3: Above/Beyond/Reach/Stretch Codes and Green Building Programs
|ANSI/ASHRAE/IES/USGBC Standard 189.1||Commercial/ High-Rise, Multi-Family Residential||Energy and water efficiency, sustainable sites, indoor environmental quality, materials and resources, building impact on atmosphere. Developed for code adoption.|
|Collaborative for High Performing Schools||Commercial||25% more energy-efficient than ASHRAE 90.1-2004.|
|Core Performance Guide (NBI)||Commercial||20–30% more energy-efficient than ASHRAE 90.1-2004.|
|Earth Advantage||Commercial||15% above IECC, minimum EnergyStar.|
|EarthCraft House||Commercial/Residential||Builds on IECC and EnergyStar.|
|Energy Star (EPA)||Residential||15% more energy efficient. In NY, local jurisdictions may adopt as minimum energy code.|
|Green Globes (GBI)||Commercial||Emissions, energy, indoor environment, siting, water, resources, project management requirements|
Green Guidelines (NAHB)
|Residential||15—40% more energy-efficient than IECC 2003 or local code.|
|Green Points Rating System||Residential (California)||15% more energy-efficient than California's Energy Code 2005. Mandatory in some jurisdictions.|
|Home Energy Rating System (HERS)||Residential||Boulder County, CO mandated HERS index for new homes|
|ICC-700 National Green Building Standard||Residential||15% more energy-efficient than IECC 2006|
|International Green Construction Code (IgCC)||Commercial/High-Rise, Multi-Family Residential||30% minimum energy efficiency over IECC 2006. Adopting jurisdictions can select which portions are applicable. Addresses air quality, energy, materials, siting, and water. ASHRAE 189.1 is an alternate compliance path.|
|The Living Building Challenge (CRGBC)||Commercial/Residential||100% on-site renewable energy, net-zero energy on annual basis; net-zero water consumption, 100% storm water and building water discharge managed on site; materials, indoor environmental quality, siting, aesthetic requirements.|
|LEED (USGBC)||Commercial/Residential||10% compliance above ASHRAE 90.1-2007. Many local jurisdictions have adopted as mandatory standard.|
|PHIUS+ Passive Building Standard||Commercial/Residential||Enhanced indoor air quality (IAQ) and building durability. Third-party (RESNET) verification.75% reduction in space heating and cooling as compared to IECC.|
Local Green Building Policies and Programs
The expanded market interest in green homes has driven an increase in the number of green building programs across the country.4 In general, local green home building programs offer building professionals and home owners a localized system to measure or rate the "greenness" of a home building project. These programs also provide valuable information on the benefits of green building and of buying green-built homes. Some local programs offer resources and incentives to build green and provide training to help home builders design and construct green homes.
Case Study: Green Affordable Housing, New York Habitat for Humanity
In 2011, New York Habitat for Humanity constructed a four-story apartment building in Brooklyn, New York, known as the Atlantic Avenue Project. Unlike other Habitat for Humanity projects, Atlantic Avenue incorporated many green building strategies. The energy efficiency measures are expected to save future residents up to thirty percent on their electricity bills.
Case Study: Voluntary Program, Cascadia Region Green Building Council
The Cascadia Region Green Building Council developed the Living Building Challenge, arguably one of the most aggressive building rating programs available. The program contains a series of prerequisites, all of which a building must achieve in order to qualify. The challenge addresses several topics, including: water, materials, energy, site, indoor quality, and aesthetics. The stringent requirements state that buildings must be 100% water and energy-efficient, meaning that all energy must be generated on-site by renewable resources and all water must be collected and treated on site.
Designed by Hellmuth & Bicknese and completed in 2009, Washington University at St. Louis' Tyson Living Learning Center is seeking to be one of the first Living Building Challenge-certified structures. To meet the requirements, rainwater from the building is collected and processed through a filter before it is stored in a 3,000-gallon, below-ground cistern. The system is able to supply water for the building for 60 days without rain.
Materials choices were also scrutinized. For example, the pavement surrounding the building is porous and will absorb almost all storm runoff. A 17-kilowatt photovoltaic system will provide power for the facility. The landscaping includes a rain garden planted with Missouri-native plants. In addition to the exposed Eastern Red Cedar exterior and interior wood, the building includes Red Maple, Black Walnut, Ash and Hickory that was either from fallen trees or from trees slated for removal as part of the restoration activity on the Tyson grounds. The structural wood came primarily from Pocahontas, Ark., approximately 200 miles away—well within the 500-mile requirement to reduce carbon emissions from transporting materials.
In addition to codes and standards, there are also a number of voluntary green building programs that go beyond code and push green building to the next level. Some of the most prominent voluntary green building programs are EnergyStar, USGBC's LEED and
NAHB's Green Building Standard. Many homebuilders apply for these extra programs to get recognition and publicity for their green building efforts. A recent study of commercial buildings by CoStar, a real estate information company, found that LEED-certified buildings have higher occupancy, lower operating costs, and higher sale prices.5
Prescriptive vs. Performance
In order to comply with code requirements, architects, builders, and developers generally must follow a prescriptive, performance-based, or trade-off path. The following descriptions discuss each path in the context of complying with energy building codes. Energy building codes provide requirements for building enclosure components, lighting systems, water heating systems, and mechanical systems.
A Prescriptive path is a fast, definitive, and conservative approach to code compliance. Materials and equipment must meet a certain levels of stringency, which are quantified in tables.6 These tables list the minimum and maximum requirements for insulation values of materials, the allowable watts per square foot of lighting systems and the minimum energy efficiencies required of mechanical systems. A prescriptive path dictates specific requirements that must be met, but does not account for potentially energy-saving features like window orientation.
Performance-based codes are designed to achieve particular results, rather than meeting prescribed requirements for individual building components. Performance paths typically are based on the anticipated results from application of the prescriptive path. This path is useful when quantifying non-traditional building features, such as passive solar and photovoltaic technology7 . Performance-based approaches use an established baseline measurement from which certain systems must perform. A performance-based path requires more detail regarding building design, materials, and systems; yet is a more flexible approach than the prescriptive path.
Outcome-based codes establish a target energy use level and provide for regular measurement and reporting of energy use to assure that the completed building performs at the established level. Such a code can have significant flexibility to reflect variations across building types and can even cover existing or historic buildings. Most importantly, outcome-based codes can address all energy used in buildings and provide a metric to determine the actual quality of the building construction.
Trade-off paths offer a middle of the line approach to code compliance. The approach seeks to achieve a balance of energy-efficient materials and systems. All components do not have to adhere to the stated requirements. However if one component is less energy efficient, than another must exceed the requirements, creating a balance.
Beyond development of stretch codes for energy and green buildings, programs are developing to support increased resilience in the face of natural hazards, including the Insurance Institute for Business and Home Safety (IBHS) FORTIFIED program. Building Information Modeling (BIM) is also emerging within the home building industry as a tool to support efficient design and assist in incorporation of high performance building attributes.
1 [Environmental Protection Agency, Analysis of the Life Cycle Impacts and Potential for Avoided Impacts Associated with Single-Family Homes .]
2 [EPA, Building Codes for Radon-Resistant New Construction (RRNC)]
5 [The American Institute of Architects, Local Leaders in Sustainability: A Study of Green Building Programs in Our Nation's Communities .]
6 [Dermisi, Sofia. "Effect of LEED Ratings and Levels on Office Property Assessed and Market Values", The Journal of Sustainable Real Estate, vol.1 .]