elements of an energy efficient house (2000) us dept of energy

7/28/2019 Elements of an Energy Efficient House (2000) US Dept of Energy

1/8

You have much to consider when design-

ing and building a new energy-efficienthouse, and it can be a challenge. However,recent technological improvements inbuilding elements and construction tech-niques also allow most modern energy-saving ideas to be seamlessly integratedinto house designs while improving com-fort, health, or aesthetics. And eventhough some energy-efficient features areexpensive, there are others that manyhome buyers can afford.

While design costs, options, and styles

vary, most energy-efficient homes havesome basic elements in common: a well-constructed and tightly sealed thermalenvelope; controlled ventilation; properly

sized, high-efficiency heating and cooling

systems; and energy-efficient doors, win-dows, and appliances.

Thermal Envelope

A thermal envelope is everything aboutthe house that serves to shield the livingspace from the outdoors. It includes thewall and roof assemblies, insulation,air/vapor retarders, windows, and weath-erstripping and caulking.

Wal l and Roof A ssembli es

Most builders use traditional wood frameconstruction. Wood framing is a triedand true construction technique that usesa potentially renewable resourcewood

Elements of anEnergy-Efficient HouseC

LEARIN

GHOUSE

ENERGYEFFICIENCY

AND

RENEWABLEENERGY

TOFENERGY

DEPARTM

EN

U

E

NITED

STAT S OFA

ER

ICA

M

This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory.The document was produced by the Information Services Program, under the DOE Office of Energy Efficiency and Renewable Energy. The Energy Efficiencyand Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based oninformation known to EREC and NRELat the time of printing. No recommendation or endorsement of any product or service is implied if mentioned by EREC

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste

DOE/GO-10200-107FS-207

July 2000

This house in Illinois has many energy-efficient features, including advanced framing tech-niques, insulated sheathing, and an advanced ductwork system. It was built by Town and Coun-try Homes as part of DOE's Building America Program.


2/8


3/8

attics. The air condenses as it cools. Thesame can be said for southern climates,just in reverse. As the humid outdoor airenters the walls and encounters coolerwall cavities, it condenses into liquidwater. This is the main reason why somebuildings in the South have problems withmold and rotten wood after theyre retro-fitted with air conditioners.

A vapor retarder is a material or structuralelement that can be used to inhibit themovement of water vapor, while an airretarder can inhibit airflow, into and out ofa houses envelope. How to design andinstall vapor retarders depends a greatdeal on the climate and on the chosen con-struction method. However, any watervapor that does manage to get into thewalls or attics must be allowed to escape.

Regardless of climate, water vapor migra-tion should be minimized by using a care-fully designed thermal envelope andsound construction practices. Systems thatcontrol air and water vapor movement inhomes rely on the nearly airtight installa-tion of sheet materials on the interior asthe main barrier.

The Airtight Drywall Approach (ADA)uses the drywall already being installedalong with gaskets and caulking to create a

continuous air retarder. In addition, seamswhere foundation, sill plate, floor joistheader, and subfloor meet are also care-fully sealed with appropriate caulk or gas-ket material.

Consult your local building codes officialon the best vapor retarder method to usein your area.

Windows

The typical home loses more than 25 per-cent of its heat through windows. Evenmodern windows insulate less than a wallTherefore, an energy-efficient house in aheating-dominated climate should, in gen-eral, have few windows on its northern,eastern, and western sides. Total windowarea should also not exceed 8 to 9 percentof the floor area for those rooms, unlessthe designer is experienced in passive

solar techniques. If this is the case, thenincreasing window area on the southernside of the house to about 12 percent ofthe floor area is recommended. This isoften called solar tempering.

A properly designed roof overhang forsouth-facing windows will help preventoverheating in the summer. North, east,

3

The best windows

are awning and

casement styles

because these styles

often close tighter

than sliding types.

This house in Arizona features a passive solar design with overhangs above the southfacing windows.


4/8

and west windows should have low SolarHeat Gain Coefficients (SHGC). Southwindows with properly sized overhangsshould have a high SHGC to allow wintersun (and heat) to enter the house. Theoverhang blocks the high summer sun(and heat). If properly sized overhangs arenot possible, a low SHGC glass should be

selected for the south windows.

At the very least, you should use windows(and doors) with an Energy Star label,which are twice as energy efficient asthose produced 10 years ago, according toregional, climatic guidelines (note: houseswith any kind of solar tempering haveother guidelines). The best windows areawning and casement styles because theseoften close tighter than sliding types. In allclimates, window glass facing south with-out overhangs can cause a problem on thecooling side that far exceeds the benefitfrom the winter solar gains.

Weatherstr i pping and Caulk i ng

You should seal air leaks everywhere in ahomes thermal envelope to reduce energyloss. Good air sealing alone may reduceutility costs by as much as 50 percent

when compared to other houses of thesame type and age. You can accomplishmost air sealing by using two materials:caulking and weatherstripping. Caulkingcan be used to seal areas of potential airleakage into or out of a house. And weath-erstripping can be used to seal gapsaround windows and exterior doors.

Controlled Ventilation

Since an energy-efficient house is tightlysealed, it needs to be ventilated in a con-trolled manner. Controlled, mechanicalventilation prevents health risks fromindoor air pollution, promotes a morecomfortable atmosphere, and reduces airmoisture infiltration, thus reducing thelikelihood of structural damage.

Furnaces, water heaters, clothes dryers,

and bathroom and kitchen exhaust fansexpel air from the house, making it easierto depressurize an airtight house if all elseis ignored. But natural-draft appliancesmay be back-drafted by exhaust fans,which can lead to a lethal buildup of toxic

4

Good air sealing alone

may reduce utility

costs by as much as

50 percent.

Air leakage can occur in many places throughout a home.

Joint betweenbottom plateand floor

Holes throughair-vaporbarrier

Electricaloutlets and switches

CracksarounddoorsElectrical

panel

Vents frombathroom andkitchen

Joints atattic hatch

Joint betweenjoists and basement wall

Serviceentrance for

cable TV,telephone,

fuel, etc.

Electrical

service

entrance

Electric meter

Jointsbetween wall

and ceiling

Jointsat windows

Joints atinterior partitions

Ceiling lightfixture

Electrical wirespenetrating

vapor barrier

Chimneypenetration

of ceiling

Plumbingstack

penetration


5/8

gases in the house. For this reason, sealed-combustion heating appliances, which useonly outside air for combustion and ventcombustion gases directly to the outdoors,are very important for ventilation energyefficiency and safety.

Heat recovery ventilators (HRV) or energyrecovery ventilators (ERV) are growing inuse for controlled ventilation in airtight

homes. These ventilators can salvageabout 70 percent of the energy from thestale exhaust air and transfer that energyto the fresh air entering by way of a heatexchanger inside the device. They can beattached to the central forced air system ormay have their own duct system.

Other ventilation devices, such asthrough-the-wall or trickle vents, maybe used in conjunction with an exhaustfan. They are, however, more expensive tooperate and possibly more uncomfortableto use because they have no energy recov-ery features to precondition the incomingair. Uncomfortable incoming air can be aserious problem in northern climates andcan create moisture problems in humid cli-mates. Therefore, this ventilation strategyis only for arid climates. Other systemspull outside air in with a small outsideduct on the return side of the furnace.

Heating and Cooling Systems

Specifying the correct sizes for heating andcooling systems in airtight, energy-efficienhomes can be tricky. Rule-of-thumb sizingis often inaccurate, resulting in wastefuloperation. Conscientious builders andheating, ventilation, and air-conditioning

contractors size heating and coolingequipment based on careful considerationof the thermal envelope characteristics.

Generally, energy-efficient homes requirerelatively small heating systems, typicallyless than 50,000 Btu/hour even for verycold climates. Some require nothing morethan sunshine as the primary source ofheat along with auxiliary heat from radi-ant in-floor heating, a standard gas-firedwater heater, a small boiler, a furnace, orelectric heat pump. Any common appli-

ance that gives off waste heat can alsocontribute significantly to the heatingrequirements for such houses.

If an air conditioner is required, its often asmall unit and sufficient for all but thewarmest climates. Sometimes only a largefan and the cooler evening air are neededto make the house comfortable. The houseis closed up in the morning and stays cooluntil the next evening.

Smaller-capacity heating and cooling sys-

tems are usually less expensive to buy andoperate. This helps recover the costs ofpurchasing more insulation, and otherenergy-efficient products, such as win-dows and appliances. Always look for theEnergyGuide label on heating and coolingequipment. The label will rate how effi-cient it is as compared to others availableon the market.

In climates where summer cooling require-ments dominate, light-colored materialsand coatings (paint) on the exterior sidingand roof can help reduce cooling require-ments by up to 15 percent. Carefullyselected and placed vegetation in any cli-mate also contributes to reduced coolingand heating loads.

5

Generally, energy-

efficient homes

require relatively

small heating systems.

Heat recovery ventilation.

Outsideair inlet

Air-to-airheat exchanger

Stale roomair return

Fresh airsupply Exhaust

air


6/8

Energy-Efficient Appliances

Appliances with relatively high operatingefficiencies are usually more expensive topurchase. However, higher efficiencyappliances provide a measure of insuranceagainst increases in energy prices, emitless air pollution, and are attractive selling

points when the home is resold.

Home buyers should invest in high-effi-ciency appliancessuch as water heaters,clothes washers and dryers, dishwashers,and refrigeratorsespecially if theseappliances will be used a great deal.Because all major appliances must have anEnergyGuide label, read the label carefullyto make sure you buy the most efficientappliance. To help you choose wisely,major appliances with an Energy Star

label exceed the federal governments

minimum efficiency standards by a largepercentage.

Energy-efficient lighting helps keepenergy bills down by producing less heatand reducing cooling requirements. Fluo-rescent lighting, both conventional tubeand compact, is generally the most energy-efficient for most home applications.

Advantages and Disadvantages

Houses that incorporate all of the above

elements of energy efficiency have manyadvantages. They feel more comfortablebecause the additional insulation keepsthe interior wall at a more comfortableand stable temperature. The indoorhumidity is also better controlled, anddrafts are reduced. A tightly sealedair/vapor retarder reduces the likelihoodof moisture and air seeping through thewalls. They are also very quiet because theextra insulation and tight constructionhelps to keep exterior noise out better.

But these houses also have some potentialdisadvantages. They may cost more andtake longer to build than a conventionalhome if theres a lack of builder familiaritywith new construction techniques andproducts available on the market. Eventhough the houses structure may differonly slightly from conventional homes,the builder and contractors may beunwilling to deviate from what theyve

always done before. They may need moretraining if they have no experience withthese systems.

Building and Buying

Before you start a home-building project,the building site and its climate should be

carefully evaluated to determine the opti-mum design and orientation for thehouse. There are energy-related computersoftware programs that can help withthese evaluations. The design shouldaccommodate appropriate insulation lev-els, moisture dynamics, and aesthetics.Decisions regarding appropriate win-dows, doors, and heating, cooling andventilating appliances are central to anefficient design. Also the cost, ease of con-struction, the builders limitations, andlocal building code compliance should be

competently evaluated. Some plans arerelatively simple and inexpensive to con-struct, while others can be extremely com-plex and, thus, expensive.

An increasing number of builders are par-ticipating in the federal governmentsBuilding America and Energy Star

Homes programs, as well as local homeenergy rating programs, all of which pro-mote the construction of energy-efficienthouses. Many of these builders constructenergy-efficient homes to differentiate

themselves from their competitors. Con-struction costs can vary significantlydepending on the materials, constructiontechniques, contractor profit margin, expe-rience, and the type of heating, cooling,and ventilation system chosen.

Because energy-efficient homes requireless money to operate, many lenders nowoffer energy-efficient mortgages (EEMs).EEMs typically have lower points andallow for the stretching of debt-to-incomeratios. State and local government energyoffices can be contacted for information onregion-specific financing.

In the end, your energy-efficient housewill provide you with superior comfortand lower operating costs, not to mentiona higher real estate market value.

6

Higher efficiency

appliances provide a

measure of insuranceagainst energy prices

and emit less air

pollution.

The building site

and its climate shouldbe carefully evaluated

to determine the

optimum design.


7/8

7

Resources

The following are sources of additional information onenergy-efficient houses:

The Energy Efficiency and Renewable EnergyClearinghouse (EREC)P.O. Box 3048

Merrifield, VA 221161-800-DOE-EREC (1-800-363-3732)E-mail: [email protected] site: http://www.eren.doe.gov/consumerinfo/

EREC provides free general and technical information to thepublic on many topics and technologies pertaining to energyefficiency and renewable energy.

Organizations

American Solar Energy Society, Inc. (ASES)2400 Central Avenue, G-1Boulder, CO 80301Phone: (303) 443-3130; Fax: (303) 443-3212E-mail: [email protected]

Web site: http://www.ases.orgA national advocacy organization dedicated to the use of solarenergy in buildings.

Building AmericaU.S. Department of EnergyOffice of Building Systems, EE-411000 Independence Avenue, SWWashington, D.C. 20585-0121Web site: http://www.eren.doe.gov/buildings/building_america/

Works with the home building industry to produce qualityhomes that use up to 50 percent less energy without costingmore to build.

Efficient Windows CollaborativeAlliance to Save Energy1200 18th Street NW, Suite 900Washington, D.C. 20036Phone: (202) 857-0666; Fax: (202) 331-9588E-mail: [email protected] site: http://www.efficientwindows.org/

Provides unbiased information on the benefits of energy-effi-cient windows, descriptions of how they work, and recom-mendations for their selection and use.

Energy Star

U.S. Department of Energy and U.S. EnvironmentalProtection AgencyPhone: (888) STAR-YES (1-888-782-7937)E-mail: [email protected] site: http://www.energystar.gov/

Provides lists of Energy Star-qualified products, includingappliances and windows, as well as information on its energy-efficient homes program.

Lawrence Berkeley National LaboratoryBuilding Technologies DepartmentMS 90-3111Berkeley, CA 94720 USAPhone: (510) 486-6845; Fax: (510) 486-4089Web site: http://eetd.lbl.gov/btp/btp.html

Provides information on past and current research in buildingsenergy efficiency.

National Renewable Energy LaboratoryThe Center for Buildings and Thermal Systems1617 Cole Blvd.Golden, CO 80401Web site: http://www.nrel.gov/buildings_thermal

Provides information on energy-efficient buildings.

Oak Ridge National Laboratory (ORNL)Buildings Technology CenterP.O. Box 2008, MS-6070Oak Ridge, Tennessee 37831-6070Phone: (865) 574-5206; Fax Number: (865) 574-5227Web site: http://www.ornl.gov/ORNL/BTC/

Provides information on research in buildings energy effi-ciency.

Sustainable Buildings Industry Council (SBIC)1331 H Street, NW, Suite 1000Washington, DC 20005-4706Phone: (202) 628-7400; Fax: (202) 393-5043E-mail: [email protected] site: http://www.sbicouncil.org

Promotes the use of energy-efficient and passive solar buildingdesign and construction.

Web Si t es

Building Energy Software ToolsU.S. Department of EnergyOffice of Building Technology, State and CommunityProgramsWeb site: http://www.eren.doe.gov/buildings/tools_directory/

Describes many energy-related software tools for buildings,with an emphasis on renewable energy, and energy efficiency.

Cool Roof Materials DatabaseLawrence Berkeley National LaboratoryWeb site: http://eetd.lbl.gov/coolroof/

Assists with the selection of roofing materials that reflectinstead of absorb the suns radiant energy.

Green BuildingsCenter of Excellence for Sustainable DevelopmentWeb site: http://www.sustainable.doe.gov/buildings/gbintro.htm

Provides information and links on energy-efficient buildings.

(Continued on page 8)


8/8

8

Continued from page 7

The Residential Energy Efficiency DatabaseWeb site: http://www.its-canada.com/reed/

Provides a wide-range of information on energy-efficienthouses, including house plans.

Zip Code Insulation Database

Oak Ridge National LaboratoryWeb site:http://www.ornl.gov/~roofs/Zip/ZipHome.html

Provides information by zip code on the most economic insula-tion levels for new or existing homes.

Reading List

The following publications provide further informationabout energy-efficient home elements. The list is notexhaustive, nor does the mention of any publication con-stitute a recommendation or endorsement.

Books, Pamphl et s, and Report s

Buildings for a Sustainable America Case Studies, B. Miller,ASES, 1997. Available from ASES or SBIC (seeResources).

Building Green in a Black & White World, D. Johnston,Home Builder Press, 2000; Phone: (800) 223-2665;http://www.builderbooks.com.

Consumer Guide to Home Energy Savings, A. Wilson and J.Morrill, American Council for an Energy-Efficient Econ-omy, 2000; Phone: (510) 549-9914; http://aceee.org/.

The Efficient House Sourcebook, R. Sardinsky, RockyMountain Institute. Available from SBIC (see Resources).

Energy Savers: Tips on Saving Energy and Money at Home,U.S. Department of Energy. Available in PDF and HTMLat http://www.eren.doe.gov/consumerinfo/energy_savers/ or print version from EREC (see Resources).

Fine Homebuilding: Energy-Efficient Houses, Fine Home-building magazine. Available from SBIC (see Resources).

Moisture Control Handbook: Principals and Practices forResidential and Small Commercial Buildings,J. Lstiburekand J. Carmody, Van Nostrand Reinhold Co., 1993.Available from the Building Science Corporation at (978)589-5100 (phone); (978) 589-5103 (fax); or http://www.buildingscience.com.

The Passive Solar Design and Construction Handbook, M.Crosbie (ed), J. Wiley, 1997. Available for purchase fromASES (see Resources).

Residential Windows: A Guide to New Technology andEnergy Performance,J. Carmody, S. Selkowitz, and L.Herschong, Norton Professional Books, 1996. Phone:1-800-233-4830; http://www.wwnorton.com/npb/.

Insulation Fact Sheet, U.S. Department of Energy Office ofEnergy Efficiency and Renewable Energy, 1997. Avail-able from ORNL in PDF and HTML at http://www.ornl.gov/roofs+walls/insulation/. Print version is availablefrom EREC (see Resources).

Periodicals

Energy Design Update. Published by Cutter InformationCorporation, 37 Broadway, Arlington, MA 02474-5552;Phone: (800) 964-5118 or (781) 648-8700; Web site: http://www.cutter.com. This monthly newsletter containsinformation for professionals interested in energy-efficient building technologies. Product reviews appear

regularly.Environmental Building News. 28 Birge Street, Brattleboro,VT 05301; Phone: (802) 257-7300; Web site: http://www.BuildingGreen.com. This bimonthly newsletter covers awide variety of topics.

The Journal of Light Construction. Published by Builder-burg Partners, Ltd., 932 West Main Street, Richmond, VT05477; Phone: (800) 375-5981. This monthly journal oftenfeatures articles on energy conservation techniques forthe home builder.

Home Energy Magazine. 2124 Kittredge Street, #95,Berkeley, CA 94704; Phone: (510) 524-5405; E-mail:

[email protected],; Web site: http://www.homeenergy.org/. Its a source of information on reduc-ing energy consumption in the home.

Solpan Review. Published by Drawing-Room GraphicServices, Ltd., P.O. Box 86627, North Vancouver, BC V71412 , Canada; Phone (604) 689-1841. This bimonthlynewsletter features articles on energy conservation forthe building industry, including information on newproducts and energy-efficient practices in residentialconstruction.

elements of an energy efficient house (2000) us dept of energy

Documents