|Oak Timber Frame on insulated concrete slab.|
|Same home, completed|
Which one do we use? And how much insulation is enough?
Homebuilders have both the opportunity and the obligation to do something about global warming and the energy crisis. We can build homes that use far less energy, that contribute less carbon to the atmosphere and that will be healthier to live in. And, since houses can last 50 -100 years or longer, these will be enduring contributions to the world.
The Green movement is helping to point us in the right direction, but it can be confusing. How do we sort the important from the PR? How can we know how much insulation is enough? Reducing energy use is attainable, but actual goals can be elusive. Is it effective to increase the R value of a wall by 15%, 25%, 50% or more? How do we decide?
Fortunately, there are several well-known programs that offer energy guidelines. Here is a brief, non-inclusive summary of some of these programs.
Energy Star is a joint program of the U.S. Environmental Protection Agency and the U.S. Department of Energy designed to encourage energy efficient products and practices.
Energy Star Homes must meet strict guidelines for energy efficiency, be at least 15% more energy efficient than homes built to current building codes, and include additional energy-saving features that typically make them 20–30% more efficient than standard homes. Each Energy Star home’s plans and specifications are reviewed by certified raters, who inspect the home during construction and after completion and perform a blower door test to check infiltration. This data is used to generate a computer model of the home which rates the home’s energy use on the HERS index (see below). The completed home receives a report showing the HERS index, the infiltration rate and the overall Energy Star score shown in stars. Ratings range from one star to five plus stars.
Example: A HERS index of no higher than 80 is required for an Energy Star in US Climate Zone 6 which includes all of NH except the southern tier, which is located in Climate Zone 5 where the requirement decreases to 85.
The cost of the review and testing in New Hampshire is typically paid by electric utilities. Rebates have been issued for Energy Star ratings and Energy Star appliances, but there are limited rebate funds available.
Home Energy Rating System: the HERS Index
HERS is a Home Energy Rating, established by the Residential Energy Services Network (RESNET). It is a measurement of a home’s energy efficiency. It allows buyers to compare the energy efficiency of different homes. With the HERS index, the lower the score the less purchased energy is needed.
The HERS Reference Home has a HERS Index of 100, representing the energy use of a home built to current energy codes; an Index of 0 (zero) indicates that the home uses no net purchased energy (a “Zero Energy” home, (ZEH or ZEB). A home we completed in May 2009 received a HERS index of 52, and we have identified changes that will help us achieve an even lower index.
Each 1-point decrease in the HERS Index corresponds to a 1% reduction in energy consumption compared to the HERS Reference Home. Thus, a home with a HERS Index of 85 is 15% more energy efficient than the HERS Reference Home, and a home with a HERS Index of 80 is 20% more energy efficient.
In climate zone 6, a HERS index of 80 is required for Energy Star accreditation.
Leadership in Energy and Environmental Design (LEED)
The U.S. Green Building Council (USGBC) developed LEED certification to help promote green building practices and sustainable development. It rates construction projects by awarding points for green building practices in four separate areas: sustainable sites, energy and atmosphere, materials and resources, and innovation and design process. Points are awarded for each sustainable practice. When the points are added up, a structure or project is assigned a LEED rating of Certified, Silver, Gold, or Platinum.
In energy use, LEED accreditation requires the building to attain Energy Star as a minimum, but increased insulation values will add points, as will adding renewable energy generation such as photovoltaics or wind generation.
In addition to the added cost of necessary upgrades, the cost for LEED accreditation includes a fee to the USGBC, the cost to document each green or sustainable product, the cost for several meetings of the design team, and a fee to the rating agency.
NAHB Green Building Standards
The National Association of Home Builders designed the National Green Building Standard as an alternative to the U.S. Green Building Council’s LEED rating system.
The NAHB NGBS has been formally approved by the American National Standards Institute (ANSI) and was developed in partnership with the International Code Council (ICC) to conform with the international residential building code. It provides a framework for safe and sustainable building practices in all housing types and includes provisions for both new construction and remodeled or rehabilitated residential structures.
The standards require participating builders to earn a minimum number of points in areas such as:
- Land conservation and environmental mitigation
- Site design, remediation, and lot orientation
- Resource efficiency (e.g., use of recycled and locally-available materials)
- Rainwater collection
- Construction of smaller homes to conserve resources
- Energy performance starting at Energy Star
- Use of low-VOC materials and detached garages or carports to improve indoor air quality
- Homeowner education on proper maintenance and operation to maintain green benefits throughout the life cycle of a home.
There is a fee to join the program, plus a fee to an accredited rater. For more information, go to buildgreennh.com.
DOE Building America Challenge
The US Department of Energy has developed a new initiative called the Building America Challenge as a high-performance housing recognition initiative. Houses are required to obtain a minimum of 70 on the HERS index, which they are labeling the EnergySmart Home Scale (E-Scale). In addition, the home must meet a set of best practices for durability, comfort, and indoor air quality. Our homes as designed should meet these criteria.
Zero Energy Homes
Although not an official standard, a ZEH home (or ZEB) must obtain a HERS index of 0. This level indicates that the home has increased insulation levels and uses only site generated energy such as photovoltaics or wind generation.
40/60, or 40/70
Many experts are calling for standard insulation levels of R-40 in walls and R-60 (or 70 in our climate zone) in roofs and ceilings. Some Zero Energy Homes in the northeast are built to these levels. Houses without on-site energy generation find that these levels substantially reduce the amount of energy the homeowner needs to purchase.
Passive House is a comprehensive approach to designing and building affordable, sustainable and healthy homes which use up to 90% less energy than comparable homes built to current building codes. Passive House is different from most of the “standards” in that the goal is not a particular insulation level or a particular HERS rating, but a defined level of very low energy use (4.75 kBTU/SF in the living area) without or prior to the use of site generated energy. Thus, the Passive House concept is today’s highest energy standard for home construction. These standards are more energy efficient than the programs and ideas listed above, and the extensive proliferation of the Passive Houses in Europe shows that they can be built economically. At least two European nations are using Passiv Haus standards as the minimum allowed under their building code.
The Passive House is designed using a computer modeling program called the Passive House Planning Program. When a house is completed to specifications and passes the required tests and inspections, it can be labeled a Certified Passive House.
Passive House is based on pioneering work by Americans and Canadians who built super insulated houses in the 1970s and 80s. In 1990, a Swedish professor and a German physicist fine tuned the previous research and developed a mathematical model for building extremely energy efficient buildings. They named this method Passiv Haus (sp) and built the first prototype in Germany. The concept caught on and this home and others were monitored extensively and the resulting information used in computer simulations to develop ideal construction parameters
Today there are tens of thousands of Passiv Haus buildings, both residential and commercial, throughout Europe. The Passiv Haus vision is that every family has a green home that is energy efficient, durable, comfortable, healthy and safe.
In 2002, a German architect hired by the University of Illinois built the first Passive House in the US and has subsequently founded Passive House Institute US as a clearinghouse for information and certification. At this time there are around a dozen Passive House homes in the US, but the interest is growing rapidly so that number will grow quickly.
How it works
The Passive House concept includes superinsulation, airtight construction, mechanical ventilation, passive solar where possible, elimination of most thermal bridging, and choosing home appliances, heating and ventilation units that use minimal electrical energy. A Certified designer uses the Passive House Planning Program (PHPP) to develop a computer model of the project and tests the completed house to verify that it meets the standard. Houses that meet the standards are allowed to use the term Certified Passive House.
Style and Size
Passive House techniques lend themselves to any style and any size house, using a variety of insulating materials.
Indoor Air Quality
The key to indoor comfort in Passive House is a quiet central ventilation system that is widely used in Europe but still relatively unknown in the United States. As warm, stagnant air is expelled through the energy recovery ventilator, it passes by incoming streams of fresh, cooler air, allowing up to 90% of the heat to transfer without mixing the two streams of air. This system provides superior air quality 24 hours a day. Some European ventilation units not yet available in the US can provide all necessary heat for the house. As a result, says Passive House advocate Tad Everhart, “a passive house loses very little heat and then recycles it.”
Heating and Air Conditioning Systems
Passive House is designed so that typical heating and AC systems are not needed. The actual system, which will vary by house, might be a small heat exchanger or point source heater. These savings help offset the investment in added insulation, air sealing, better windows and other upgrades to the building envelope.
Passive House uses only triple glazed windows with ultra high efficiency glass and insulated frames. At this time there are only a few US manufacturers who make windows that will qualify, leading some builders to use imported Canadian or European windows.
Passive House standards recommend the home be sited to provide southern light and passive solar heat where possible, with wide overhangs used to shade the windows in the summer. The Passive House design program takes the size, placement and shading of all the windows into consideration.
Passive House standards were designed to minimize the carbon footprint of the house.
In the United States, buildings are the largest contributor to global warming, responsible for 48% of greenhouse gas emissions. Passive House standards are the single most powerful proven building concept for reducing greenhouse gas emissions.
Soaring energy costs, rapid climate changes due to greenhouse gas emissions, and the demand for high indoor air quality all call for effective solutions from the building sector. With unparalleled super-energy efficiency and superior air quality, Passive House design also provides a solution that puts true carbon-neutrality within reach.
Frequently Asked Questions (FAQs) — Passive House Institute, US