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House | Assemblies | Components
House: Height
The most efficient house height or configuration balancing the cost and environmental impact is the 1-1/2-story house with a 2-foot knee wall. The house encloses the most useful square footage with a minimum of materials and balances energy use. The 2-story house is also efficient, with the best utilization of the foundation system.
General Guidelines
- Design simple envelopes avoiding extra corners or eccentric shapes
- Do not enclose space that is not habitable such as basements and attics
- Space under a roof structure should be utilized as habitable space
House: Basement
Whether to build a basement or other foundation type is a complex decision. A house with a basement costs more than slab-on-grade or crawl space foundations, but it can provide additional living space making the overall cost per square foot less. Basements that are not designed to livable standards (with proper daylight, egress, moisture protection, insulation and ventilation) are a great concern because they are often occupied in any case and may have significant health risks. For this reason, if a garden basement or a full basement is constructed, it should be built to "livable basement" standards. When the site and program permit a garden basement should be considered because of its lower cost and greater opportunity for windows. While slab-on-grade and crawl space foundations may appear to cost more per square foot than a basement option, there are definite tradeoffs. The quality and usability of basement space may not be equivalent to above grade space. If a no basement foundation option is selected consideration should be give to the overall house design to provide adequate storage. Life safety issues related to severe weather must also be addressed through design and construction.
House: Window Orientation 1 Story
On a relatively small, unshaded house using conventional low-mass, frame construction, orientation is not a significant factor in energy use. This occurs because passive solar gains which lower heating energy use in winter are offset by higher cooling energy use in summer. To optimize for passive solar gains in cold climates, locate the majority of glazing on the south orientation. Shading through the use of awning, overhangs, and deciduous trees is necessary to avoid unwanted heat gain during the summer months (from June to August), which if left unchecked can negate energy savings. This analysis utilized high solar gain Low-E windows to maximize passive solar gain. Low solar gain Low-E windows make orientation less of a factor. See Assemblies: Window.
Citations
Residential Windows, A Guide to New Technologies and Energy Performance, 2nd Edition. John Carmody, Stephen Selkowitz, Dariush Arasteh, and Lisa Heschong. W.W.Norton & Company 2000
Efficient Windows. The Efficient Windows Web Site is sponsored by the U.S. Department of Energy's Windows and Glazings Program in collaboration with members of the Efficient Window Collaborative (EWC). EWC members have made a commitment towards manufacturing and promoting energy efficient windows. www.efficientwindows.org
House: Window Orientation 2 Story
On a relatively small, unshaded house using conventional low-mass, frame construction, orientation is not a significant factor in energy use. This occurs because passive solar gains which lower heating energy use in winter are offset by higher cooling energy use in summer. To optimize for passive solar gains in cold climates, locate the majority of glazing on the south orientation. Shading through the use of awning, overhangs, and deciduous trees is necessary to avoid unwanted heat gain during the summer months (from June to August), which if left unchecked can negate energy savings. This analysis utilized high solar gain Low-E windows to maximize passive solar gain. Low solar gain Low-E windows make orientation less of a factor. See Assemblies: Window.
Citations
Residential Windows, A Guide to New Technologies and Energy Performance, 2nd Edition. John Carmody, Stephen Selkowitz, Dariush Arasteh, and Lisa Heschong. W.W.Norton & Company 2000
Efficient Windows. The Efficient Windows Web Site is sponsored by the U.S. Department of Energy's Windows and Glazings Program in collaboration with members of the Efficient Window Collaborative (EWC). EWC members have made a commitment towards manufacturing and promoting energy efficient windows. www.efficientwindows.org
House: Window Area 1 Story
A window-to-floor area ratio of 15% to 18% is recommended for conventional construction. This window-to-floor area ratio balances energy, first cost, and indoor environmental quality. Houses implementing passive solar strategies using thermal mass and south orientation must be evaluated on an individual basis and may require a different overall window-to-floor area ratio to achieve maximum benefit. While energy use increases with window area, the penalty is not significant when high performance windows (such as triple-glazed low-E options) are used. See Assemblies: Window.
House: Window Area 2 Story
A window-to-floor area ratio of 15% to 18% of windows recommended for conventional construction. This window-to-floor area ratio balances energy, first cost, and indoor environmental quality. Houses implementing passive solar strategies must be evaluated on an individual bases and may require a higher overall window-to-floor area ratio to achieve maximum benefit.
House | Assemblies | Components
Assemblies: Foundation
Each foundation type has distinct economic, environmental, and construction advantages and disadvantages. A frost protected shallow foundation is the least expensive, most material efficient option for non-basement construction. For a balance of cost, material efficiency and improved indoor environmental quality when a livable basement is desirable, a garden basement with a cast in place concrete wall is recommended. Priorities and trade-offs will need to be considered to determine the most appropriate foundation.
Assemblies: Floor
Each floor system option has distinct economic, environmental, and construction advantages and disadvantages. Priorities and trade-offs will need to be considered in order to select the most appropriate system for a given project. Manufactured wood I-joist are recommended considering both cost and environmental impacts. They provide the lowest first cost across a variety of joist depth and floor span, and use a minimum amount of low quality and potentially recycled material.
Assemblies: Wall
Within the conventional wood frame options, 2x6 24"o.c. advanced framing reduces whole house first cost and decreases operational costs by as much as 40% annually over conventional framing ($300 to $500 annually). Advanced framing reduces material by reducing the overall amount of lumber required. Although it requires some retraining, typical carpentry skills are adequate.
SIP construction has the least environmental impact due to reduced material resource use and increased energy efficiency. SIPs have a higher first cost, but when combined with high performance windows, first cost may be offset by reducing the size of heating and cooling equipment.
The new SEP construction system may prove to be a low cost high performance alternative to both framing and SIP construction.
Each framing system has distinct economic, environmental, and construction advantages and disadvantages. Priorities and trade-offs will need to be determined in order to select the most appropriate system for a given project.
In general when planning exterior systems the following should be considered to reduce and eliminate environmental impacts.
- Use locally or regionally manufactured wood products to reduce transportation and increase community economic benefits. Wood framing used in this region comes from the Western or Southeastern US, as well as Canada. Panel products are manufactured within 500 miles and insulations are manufactured within 1000 miles.
- Use materials which maximize rapidly renewable resources: Exterior oriented strand board (OSB) uses fast-growing aspen and waste products; however, use materials from FSC-certified producers to ensure sustainable growing and harvesting practices and prevent use of 'plantation' grown products.
- Use less toxic materials: When selecting composites (OSB), use formaldehyde-free sheathing products to protect workers and installers from the production effects. Use expanded polystyrene or polyisocyanurate insulations which do not use HCFC blowing agents in panel construction (SEP and SIP).
Citations
Forest Stewardship Council (FSC): www.fscus.org A third-party certification organization established to promote sustainable growth and harvesting practices throughout the world's forests.
Assemblies: Roof
SIP construction has the least environmental impacts due to reduced material resource use and increased energy efficiency. SIPs have a higher first cost, however, when combined with high performance windows, first cost may be offset by reduced sizing of the heating and cooling equipment.
The new SEP construction system may prove to be a low cost high performance alternative to both framing and SIP construction.
In general when planning exterior systems the following should be considered to reduce and eliminate environmental impacts.
- Use locally or regionally manufactured wood products to reduce transportation and increase community economic benefits. Wood framing used in this region comes from the Western or Southeastern US, as well as Canada. Panel products are manufactured within 500 miles and insulations are manufactured within 1000 miles.
- Use materials which maximize rapidly renewable resources: Exterior oriented strand board (OSB) uses fast-growing aspen and waste products; however, use materials from FSC-certified producers to ensure sustainable growing and harvesting practices and prevent use of 'plantation' grown products.
- Use less toxic materials: When selecting composites (OSB), use formaldehyde-free sheathing products to protect workers and installers from the production effects. Use expanded polystyrene or polyisocyanurate insulations which do not use HCFC blowing agents in panel construction (SEP and SIP).
Citations
Forest Stewardship Council (FSC): www.fscus.org A third-party certification organization established to promote sustainable growth and harvesting practices throughout the world's forests.
Assemblies: Window
Balancing cost and performance select a double low-E argon window with a performance rating of u-value of .35 or less, solar heat gain coefficient (SHGC) between .30 and .60, and a visible light transmittance VT of .50 or more. Passive solar homes should look for windows with a high solar heat gain coefficient to maximize solar gain. Always select windows with NFRC ratings that meet Energy Star criteria.
Citations
Residential Windows, A Guide to New Technologies and Energy Performance, 2nd Edition. John Carmody, Stephen Selkowitz, Dariush Arasteh, and Lisa Heschong. W.W.Norton & Company 2000
Efficient Windows. The Efficient Windows Web Site is sponsored by the U.S. Department of Energy's Windows and Glazings Program in collaboration with members of the Efficient Window Collaborative (EWC). EWC members have made a commitment towards manufacturing and promoting energy efficient windows. www.efficientwindows.org
House | Assemblies | Components
Components: Exterior Materials
Components: Certified Lumber
- Determine the highest volume uses of wood on your project and select FSC-certified products for these applications. The Certified Forest Products Council (CFPC) offers assistance identifying availability of products, www.certifiedwood.org.
- Select locally grown, certified products whenever possible to further reduce the environmental impacts associated with transportation and improve social and community benefits.
- Use domestic hardwoods in place of imported tropical products.
Components: Insulation
Loose fill, blown and batt insulation is more cost effective in walls and attics than rigid board insulation. Foamed-in-place insulation should be used when budget permits, its high R-value combined with excellent air sealing increase the overall performance of the assembly. Look for insulation materials that have stable R-values over time.
Extruded polystyrene (XPS) insulation with CFC or HCFC's as blowing agents should not be used. Rigid insulation alternatives include: wood fiberboard, (some made entirely from recycled cellulose), expanded polystyrene (EPS), fiberglass board, or cellular glass board.
Citations
Sustainable Design Resource Guide, AIA Colorado www.aiacolorado.org/SDRG
Components: Sheathing
- Use locally or regionally manufactured wood products, to reduce transportation and increase community economic benefits: Exterior Oriented Strand Board is manufactured within 500 miles of the Metro Area (closer to outstate areas)
- Use materials which maximize rapidly renewable resources: Exterior Oriented Strand Board uses fast-growing aspen and waste products; however, use materials from FSC-certified producers to ensure growing and harvesting sustainable practices and prevent 'plantation' grown products
- Use less toxic materials: When selecting composites (OSB), use formaldehyde-free products to protect workers and installers from the effects of dust and off-gassing
- When sheathing may be exposed to the elements for up to six months, choose fiberglass-faced gypsum sheathing for durability; select products with synthetic gypsum to reduce overall material resource use
Components: Cladding (siding)
The appearance of a traditional home can be achieved with fiber cement siding, which balances first cost, durability, and environmental impact and is recommended as a lap siding. Stucco should be considered as an alternative for residences that require extremely low maintenance alternatives and have an anticipated life span of 50 years or more.
General Guidelines for selecting a cladding system:
- Choose a system that will be serviceable at least through the end of the first mortgage term, usually 30 years.
- Compare life-cycle costs for siding, including first cost, maintenance costs, and replacement costs to determine best selection.
- Use products that come from sustainable sources or those made with recycled or waste material to reduce overall environmental impacts.
- Use products that are recyclable.
Components: Roofing
Although asphalt shingles have the lowest first cost, they require more frequent replacement than other options resulting higher lifetime costs. Asphalt shingles also make a significant contribution to landfills. Metal roofing and fiber cement shingles last longer than asphalt shingles without adding weight to the structure. Because metal has high recycled content and can be recycled after use, it has a favorable environmental impact.
In selecting roofing materials, consider the weight and whether additional structure is required. If so, factor the environmental impacts of that increased structure into the overall impacts of the roofing. Also consider how the roofing material affects the quality of water falling on it. For example, will it contribute sediment that may plug gutters or catchment containers?
Components: Interior Materials
Components: Paints, Stains & Coatings
- Use products which have the MPI (Master Painters Institute) recommendation: A High Performance Architectural Latex or an Institutional Low Odor / VOC product. A list of products is available at: www.specifypaint.com/APL/paintinfo_APL/ProductIdxAlphabetical.asp
- Use products with low or no VOC content and water-based formulations whenever available and appropriate to the use.
- Choose products based on their total life-cycle cost, including durability and embodied energy.
- Use products with a high recycled material content when appropriate for durability and air quality.
- Select products that can be recycled and recycle unused paint.
Components: Flooring
Based on economic and environmental impacts, ceramic tile and linoleum are recommended. Economically a higher first cost is incurred, however when durability and life time cost is considered, these products stand out. When considering carpet, look for high recycled content and products that are recyclable. New carpet tile systems are relatively inexpensive, easy to maintain and durable.
- Consider durability, maintenance requirements, and ease of cleaning when selecting flooring.
- Choose flooring that will be serviceable through the end of the first mortgage term, usually 30 years.
- Products that contain PVC have serious impacts on the environment and human health. When possible, look for alternatives to using PVC products, such as linoleum or ceramic tile.
Heating, Cooling & Ventilaion
Components: Heating (furnace)
General Guidelines
- Install a 90% or better AFUE furnace.
- Properly size the furnace for the required heating load
- If install in conjunction with air conditioning use a 13 SEER or better Air Conditioner
- Use a digital programmable thermostat to maximize the efficiency of heating and cooling systems. See Components: Programmable Thermostat for more information.
Programmable Thermostat
A programmable thermostat is a must for all new and existing housing construction. The week and weekend programmable thermostats accommodate daily schedules, offer enough flexibility for most households, offer relative ease of use, and low cost. Look for Energy Star rated models to ensure maximum energy savings and comfort.
Plumbing & Equipment
Components: Fixtures
The following recommendations are for water fixtures intend for indoor water use:
- Use low flow toilets. 1.5 gallons per flush (gpf)
- Use low-flow kitchen faucets. 2.5 gallons per minute (gpm)
- Use lavatory faucets with flow restrictors for a maximum rate of .5 gpm
- Use low-flow showerheads. 2.0 gpm
Hot Water Heater
Tankless water heaters are recommended as a balance of affordability, durability, and energy consumption. The consideration of first as well as operational cost is critical. The system has the added benefit of being wall mounted and compact, and therefore takes up less space then a traditional tank unit in a smaller home.
Solar is an economically viable option if utility service is limited to electricity and an electric water heater is the only option. It is the clear environmental winner across all types.
Install the highest available efficiency of gas water heater if a conventional system is used. The premium cost of the unit will be recouped over the life of the unit.