A Pacific Northwest organization has defined an environmentally sound structure as one that generates its own energy, captures and treats all of its water, operates efficiently, and is aesthetically pleasing. Many readers will recognize the movement as the Living Building Challenge, launched in 2006.
There are many reasons to control the amount of sunlight admitted into a building. In warm, sunny climates excess solar gain will result in overheating, in cold and temperate climates winter sun entering south-facing windows can contribute to passive solar heating, and in any event controlling and diffusing natural illumination will improve daylighting. Continue reading
Buildings are deceptively complex. At their best, they connect us with the past and represent the greatest legacy for the future. They provide shelter, encourage productivity, embody our culture, and certainly play an important part in life on the planet. In fact, the role of buildings is constantly changing. Buildings today are life support systems, communication and data terminals, centers of education, justice, and community, and so much more. They are incredibly expensive to build and maintain and must constantly be adjusted to function effectively over their life cycle. The economics of building has become as complex as its design.
Data from the U.S. Energy Information Administration illustrates that buildings are responsible for almost half (48%) of all greenhouse gas emissions annually. Seventy-six percent of all electricity generated by U.S. power plants goes to supply the building sector and buildings often contribute to health problems such as asthma and allergies due to poor indoor environmental quality. Safety is also paramount in buildings with security-related expenditures one of the fastest rising expenses.
The federal government has responded to these challenges by putting into place Executive Orders and Mandates. High performance buildings were defined in the Energy Policy Act of 2005 (Public Law 109-058) as: “buildings that integrate and optimize all major high-performance building attributes, including energy efficiency, durability, life-cycle performance, and occupant productivity”.
The Energy Independence and Security Act (EISA) of 2007 further established a new and aggressive plan for achieving energy independence in our nation’s building stock by the year 2030. The Act requires that federal buildings (new and renovations) achieve fossil fuel-generated energy consumption reductions on the order of 55 percent in the year 2010 to 100 percent in 2030. The Act also requires that sustainable design principles be applied to siting, design, and construction. It is of note that the Act defines High-Performance Buildings as the integration and optimization on a life cycle basis all major high-performance attributes, including energy conservation, environment, safety, security, durability, accessibility, cost-benefit, productivity, sustainability, functionality, and operational considerations. These issues are synonymous with whole building design.
Several programs, both public and private sector, define standards and measures for sustainable buildings. Of the government programs, the most well known and influential is Energy Star, providing an energy performance rating system applied to buildings. Of the private sector programs, the best known and most influential is the USGBC’s LEED® rating system. Others include Green Globes®, the NAHBGreen® certification system administered by the National Association of Home Builders, Greenguard®, and the Living Building Challenge® administered by thhe International Living Future Institute.
Whole Building Design encompasses all of these issues and programs and is an essential way of approaching building projects. Understanding Whole Building Design concepts will enable you to think and practice in an integrated fashion to meet the demands of today’s as well as tomorrow’s high-performance building projects.
Article based on that found at the Whole Building Design Guide website, a program of the National Institute of Building Sciences.
What is a Net-Zero Energy Home?
Net-zero simply means that a building produces as much energy as it consumes. Net-zero energy buildings (NZEBs) minimize energy use through efficiency and by meeting remaining needs through renewable energy sources. Because NZE is a relative newcomer to the construction industry, it behooves all involved to be well-educated as to the steps necessary to successful design of the NZEB.
The acid test of whether a NZE home is performing as intended generally comes an entire year after it’s constructed, when the first year of energy bills are evaluated. By then it can be far too late to correct any deficiencies in the design. Moreover implementing NZE strategies, if not done cost-effectively, can completely erase potential energy savings (operating costs) due to excessive construction costs (initial costs), thus resulting in a failed building from a costs-benefits standpoint.
To help avoid these pitfalls we’ve outlined the following ten steps towards the affordable Net-Zero Energy Home.
1. It begins with the Design Process: The first step towards the affordable NZE home begins with an integrated design process, a team approach ideally including the owner, builder, architect and an energy consultant. Obtaining a cost-effective NZE home requires that a vast array of design decisions, many normally deferred until relatively late in the design process, be effectively identified and decided right from initiation of the design. To do this effectively requires hands-on involvement from all parties, including the owner whose job it is to make the decisions, the contractor advising on cost-effective options, the analyst verifying major decisions with energy modeling, and the architect facilitating orchestrated design decisions towards the optimal result.
2. The Site: For the most cost-effective NZEB, site selection must consider climate, weather patterns, wind, sun exposure, shade, heating/cooling degree-days, and topography. Ideally one should choose a site with a long east-west lot line to allow design imperatives such adequate south-facing roof for solar collectors and south facing windows for solar gain. The site should be free of obstructions such as trees, neighboring homes, and land-forms interfering with solar access.
A solar analysis is an important tool for evaluating passive solar, solar photovoltaic (PV) and solar thermal (hot water) potential by objectively measuring a site’s limitations for solar gain potential. Taking full advantage of the solar potential for each site is one of the most cost-effective strategies for achieving the successful NZE Home.
3. The Basis of Design: After the site analysis has been concluded, the next step is for the project team to collaborate with the architect in preparing the NZE’s program brief. The “Brief” is simply a detailed, itemized list of the strategies to be implemented for this particular home on this particular site to achieve the intended goals. It thus serves as a checklist or “road map” for the project.
The Brief encapsulates key components and measures such as the building’s area, projected construction budget, size and characteristics of various rooms, appropriate construction type for foundation, walls and roof assemblies, targets for appropriate ratio of floor area to percentage of window glazing, and targeted sources for renewable energy.
4. Size and Shape Matter: When contemplating the design and construction of an affordable NZE home, size and shape matter. Smaller homes use less energy for space heating and cooling, thus reducing operating costs. The savings from building, say, a 10% smaller home that achieves the same level of comfort and livability as a standard home represents a significant lowering of the cost construction, thus improving the bottom line right from inception. The well-known strategies of the Not So Big House movement can be used to result in a smaller home designed to look and feel larger,more spacious and comfortable without wasted space, resulting in a smaller home which functions as well as a larger home without unnecessary expense. Shape is also important. For example, an axially arranged organization of rooms will increase the surface area available for south-facing windows, optimizing opportunities for passive solar gain as well as daylighting. Similarly a thin organization of rooms will increase opportunities to cross-ventilate the home, thus facilitating passive cooling.
5. Design to use the sun: To be successful, NZE homes must be designed to take advantage of the sun’s energy to the greatest extent possible, using it for example as the energy source for passive solar gain, generating electricity, and collecting solar hot water. After site analysis the conceptual model of the home can be appropriately located and massed appropriate to climate and site conditions, allowing mapping of potential energy performance and energy savings from the start.
Using this data the total area of southern-facing glazing will be determined – generally speaking it’s better to have too much rather than too little south-facing glass since excess solar gain can always be mitigated, but there is no remedy for inadequate amounts of glass.
Once the appropriate amount of glazing is determined, control features such as eaves, light shelves, trellises, horizontal louvers, brises soleil, external shades and shutters, and glass selection are used to fine tune performance to avoid excessive heat gain in the summer and optimize solar heat gain in the winter.
The design effort can then focus on the non-solar energy sources contributing to the overall energy picture by quantifying photovoltaic, solar hot water and other on-site renewable energy sources necessary to balancing the NZE home’s energy equation.
6. Design for added insulation: Think of the home as a six-sided box in which all six sides need to have the most cost-effective insulation specific to the project need. R-value is the unit of measure for insulation, and R-values on each side of the box, as determined by energy modeling, must meet but not exceed the net-zero energy goals. Once NZE goals are meet, surplus insulation in excess of project needs is not a cost-effective use of resources.
Features such as thicker walls, deeper floor framing assembly or slab-on-grade, and raised roof-truss heels may be incorporated in the design to accommodate the appropriate insulation. Here in coastal California, the design issues are relatively less challenging. Nonetheless, as with any other aspect of the design, it is important that these strategies be weighed, decided upon, mapped, and incorporated into the design documentation to ensure that the subcontractors on the jobsite understand unambiguously the design intent and how it is to be built in order to ensure success.
More challenging climate zones such as inland California, the Mountain States and Midwest may require measures such as 8-inch to 12-inch thick, off-set stud walls to provide for adequate insulation. Moisture related issues must also be considered in the design of the highly insulated and airtight building assemblies of the NZEB. Designing assemblies that are both breathable and airtight prevents moisture-related issues in the realized building.
7. Minimize thermal bridging: During the course of the design thermal bridging must be eliminated as much as possible from all six sides of the six-sided box. A slab-on-grade foundation system for instance is always placed atop an insulative barrier separating it from grade. In conventionally framed walls, every nail, every screw, and every stud in the wall assembly is a potential thermal bridge. For this reason advanced framing using offset studs are coming into favor. An alternative is the use of outboard rigid insulation, which must be carefully detailed if thermal bridging is to be avoided.
8. Windows and doors: If the NZE home is a well-insulated, highly airtight, “six-sided box,” windows and doors are relatively poorly insulated “holes” in that box. Moreover they are far and away the most expensive element in the wall assemblies that make up that “box”. For these reasons optimizing the location and size of openings is among the most important design strategies for achieving the affordable Net-Zero Energy Home.
Generally, most glazing will be south-facing, with lesser amounts allocated to east and west facades. North-facing glazing will be minimized. The exact ratios will be evaluated, determined by the energy modeling, and captured into the design documents. In terms of detailed requirements and by way of example, casement and fixed windows are less susceptible to infiltration than sliding, single- or double-hung windows. Fewer, larger windows are more energy efficient and more cost effective than more, smaller windows because there is a higher glass-to-frame ratio in larger units.
9. Alternative Construction Technologies: Although conventional wood framing and it’s derivative, advanced framing (a.k.a. optimum value engineering) are most commonly in use, many other construction technologies lend themselves to NZE. Systems which might lend themselves to a satisfactory result and which might be considered include timber framing, Structural Integrated Panels (SIPs), Insulating Concrete Forms (ICFs), Wood Waste Masonry, strawbale, rammed earth, PISE, and traditional wattle and daub techniques.
In each case the technology of choice will be a function of the owner’s preferences, the builder’s familiarity and comfort level with the technology, and the costs-benefits accruing to its implementation specific to the project.
10. Design for builders: Given that the NZEB is a relatively newcomer to the construction scene, a great many of the kit-of-parts contributing to the successful NZEB will benefit from reality-checking for constructability and cost-effectiveness to build from an experienced contractor. For this reason, as mentioned previously, we generally encourage bringing the builder on board early in the design process, when ground-floor decisions informing subsequent stages of the design process are being made. Although not an absolute essential, having a contractor either as an integral member of the design team or in a consulting capacity will facilitate cost-effective decision-making right from project inception.
While building an affordable Net-Zero Energy homes is within reach of anyone who is in a position to commission a new or remodeled home, the too-be-desired results – namely affordable initial (construction) costs plus high return on investment in the form of low recurring (energy) costs – requires a host of sound decisions, systematic design and documentation, and a concerted, diligent construction effort to realize. We hope the foregoing 10 points have provided you guidance towards that end.
NZEB is one of many aspects of sustainable practice with which we have experience. To see more examples of our work in green building design click HERE.
A reader recently queried in response to our recent posting The Brave New World of Insulating Wall Assemblies, “will adding exterior insulation act to decrease the probability of a condensation issue”?
The short answer is, adding exterior insulation will always decrease the risk of condensation within the wall assembly.
That said, in the design of the entire wall assembly including insulation in the stud bay + outboard insulation, we want to design the whole assembly with the dew point outboard of the wall sheathing. That way condensation, in the rare event it does occur, does not take place within the stud bay.
The chart at right provides recommendation for balancing the insulation. In a commercial application we can assume indoor RH of 35%. In Santa Cruz, the average for the coldest three winter months (Dec, Jan, Feb) is 49.7 degrees. Cross-indexing these (35% x 50 deg F) results in 0.00. In other words, in our climate zone since temperatures are mild, insulation balancing is not likely to be a consideration.
The most conservative estimate might assume an indoor RH at the highest end of the spectrum i.e. 60%. In the same temperature range (50 deg F) this results in a 24% ratio for the exterior insulation. If we seeking to attain an R-20 wall this means it’s recommended to design R-4.8 into the exterior insulation, and the remainder (20.0 – 4.8 = 15.2) in the cavity. Using conventional insulation, options might include: A. R14 batt + R6 rigid = R20 target B. R19 batt + R1 rigid = R20 target. Since the ratio is less than 24%, Option A is the better of the two, since it is the least likely of the two option to result in condensation within the cavity.
There is a detailed and comprehensive article at Building Science.com: http://www.buildingscience.com/documents/digests/bsd-controlling-cold-weather-condensation-using-insulation. It’s author, Dr. John Straube of the University of Waterloo, is widely considered to be an authority on the subject of moisture transport within building materials and systems.
The effective date for the 2013 California Title 24 Building Energy Efficiency Standards (a.k.a. California Energy Code) will be July 1st, 2014. This update requires single-family residential buildings to be 25 percent, multi-family to be 14 percent and non-residential buildings to be 30 percent more energy efficient than the previous 2008 standard.
Under the prescriptive method, new requirements for the residential building envelope entail increasing the cavity insulation value from R-13 to R-15. Additionally, an additional layer of minimum R-4 rigid insulation will need to be applied outboard of the wall cavity.
It should be noted that these requirements apply under the prescriptive method. Equivalent wall assemblies can be supported if they “pencil” out according to the building’s energy modeling analysis.
That said, the addition of rigid insulation does vastly improve the performance of the wall assembly, and by 2016, will become a mandatory feature. So it’s best to understand the ramifications of so doing.
These considerations include: 1). selection of the appropriate rigid insulation, 2). method of attachment of the rigid material to the structural sheathing, 3). attentiveness to position of the dew point within the assembly and, 4). method of attachment of the finish material to the rigid insulation.
The standard wall assembly currently in use has benefited from generations of trial and error to perfect. The addition of rigid insulation to the assembly is in its relative infancy.
Thus, as yet there is no standardized approach guaranteed to perform reliably in the long term i.e. over the life of the building not experience any of the failure modes implied by the four considerations listed.
Implied potential failure modes include:
1). inappropriate rigid insulation: deterioration or delamination.
2). ill-considered insulation attachment: separation from substrate.
3). ignorance of dew point: liquid water within wall system.
4). ill-considered finish attachment: detachment or failure of finish material.
The prudent builder or designer striding bravely into the brave new world of rigid insulation will do well to research quite carefully the appropriate wall assembly solution, one that performs as intended while avoiding the potential pitfalls inherent in the assembly.
On March 19th, 2014 at ADPSR’s Better Envelope Solutions Showcase in San Francisco, architect Larry Strain presented a talk entitled, “Insulating Exterior Assemblies”. In it, he discussed in detail the nature of these concerns, options with respect to “green” insulation options in the assembly, together with an example of practical application in a realized project. The link is at: Insulating Exterior Assemblies.
The noted American green building architect William McDonough is famously quoted as once saying that buildings should, among other qualities, “live off current solar income”. What was merely a hypothetic concept in the early 1990’s has since firmly taken root: Net zero energy (NZE) has taken on significant momentum as one of the factors shaping the sustainable construction movement.
With the U.S. Department of Energy’s 2009 mandate that all new federal buildings will be NZE by 2030, deployment of NZE is now national policy. Beginning with the city of Austin, TX in 2009, local jurisdictions have since followed suit. Here in California, the next iteration of the Title-24 Energy Code (scheduled for July 1st) will require all new residential buildings to be NZE by 2020 and new commercial buildings to conform by 2030. As a relatively new concept in the construction industry, much ambiguity still exists as to terminology, definitions, and usage of the term Net Zero Energy.
A useful description can be found in “Sustainable Construction: Green Building Design and Delivery” which offers, “In general, these are grid-connected buildings that export excess energy produced during the day and import energy in the evenings, such that there is an energy balance over the course of the year. As a result, NZE buildings have a zero annual energy bill with the added bonus that they are considered to be carbon neutral with respect to their operational energy.”
In her popular and highly influential book Energy Free: “Homes for a Small Planet” (Green Building Press, San Rafael, CA), Ann Edminster offers four (4) definitions, each taken from a different perspective e.g. energy usage at the project site, usage at the energy source, cost of the energy used, and by emissions associated with the energy usage. Of these, the most useful are the first and the last.
The first of these, again taken from the perspective of the building, reads: “Net-zero site energy (Definition 1). A site zero energy building produces at least as much energy as it uses in a year when accounted for at the site”.
The fourth definition reads, “Net-zero energy emissions (Definition 4). A net-zero emissions building produces at least as much emissions-free renewable energy as it uses from emissions-producing energy sources.”
In Europe, the most influential leadership towards NZE seems to be that of the International Energy Agency (IEA), an NGO based in France. Working within the framework of IEA’s “Solar Heating and Cooling Program Task 40: Energy in Buildings and Communities” initiative, researchers in 14 European countries plus the U.S., Canada, Singapore, Korea, Japan, Australia, and New Zealand are working to bring NZE into international market viability.
A good exemplar of an NZE building in this county is the National Renewable Energy Laboratory’s Research Support Facility (RSF), located in Golden, Colorado. This 360,000-square-foot, four-story office building’s energy use goal is estimated at 34.4 kBTU/ft2/yr. According to U.S. EPA’s Energy Star, the national median site EUI for office buildings is 67.3 kBTU/ft2/yr, making the RSF approximately 50% more efficient than it’s conventional counterparts.
To learn more about NZE, some helpful resources include the U.S. Department of Energy Building America website, that of the Solar Heating and Cooling Programme, and Zero Energy Buildings: A Critical Look at the Definition.