Elements of an Energy-Efficient House

You have much to consider when design-

ing and building a new energy-efficient

house, and it can be a challenge. However,

recent technological improvements in

building elements and construction tech-

niques also allow most modern energy-

saving ideas to be seamlessly integrated

into house designs while improving com-

fort, health, or aesthetics. And even

though some energy-efficient features are

expensive, there are others that many

home buyers can afford.

While design costs, options, and styles

vary, most energy-efficient homes have

some basic elements in common: a well-

constructed and tightly sealed thermal

envelope; controlled ventilation; properly

sized, high-efficiency heating and cooling

systems; and energy-efficient doors, win-

dows, and appliances.

Thermal Envelope

Athermal envelope is everything about

the house that serves to shield the living

space from the outdoors. It includes the

wall and roof assemblies, insulation,

air/vapor retarders, windows, and weath-

erstripping and caulking.

Wall and Roof Assemblies

Most builders use traditional wood frame

construction. Wood framing is a “tried

and true” construction technique that uses

a potentially renewable resource—wood—

Elements of an

Energy-Efficient House

CLEARINGHOUSE

ENERGY

EFFICIENCY

AND

RENEWABLE

ENERGY

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 Efficiency

and Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based on

information known to EREC and NREL at 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-10200-1070

FS-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.

Photo by Sara Farrar, NREL/PIX07134

to provide a structurally sound, long-last-

ing house. With proper construction and

attention to details, the conventional

wood-framed home can be very energy-

efficient. It is now even possible to pur-

chase a sustainably harvested wood.

Some of the available and popular energy-

efficient construction methods include the

following:

Optimum Value Engineering (OVE). This

method uses wood only where it is most

effective, thus reducing costly wood use

and saving space for insulation. The

amount of lumber has been determined to

be structurally sound through both labora-

tory and field tests. However, the builder

must be familiar with this type of construc-

tion to ensure a structurally sound house.

Structural Insulated Panels (SIPs). These

sheets are generally made of plywood or

oriented-strand board (OSB) that is lami-

nated to foam board. The foam may be 4

to 8 inches thick. Because the SIP acts as

both the framing and the insulation, con-

struction is much faster than OVE or stick

framing. The quality of construction is

often superior because there are fewer

places for workers to make mistakes.

Insulating Concrete Forms (ICF). Houses

constructed in this manner consist of two

layers of extruded foam board (one inside

the house and one outside the house) that

act as the form for a steel-reinforced con-

crete center. It’s the fastest technique and

least likely to have construction mistakes.

Such buildings are also very strong and

easily exceed code requirements for areas

prone to tornadoes or hurricanes.

Insulation

An energy-efficient house has much higher

insulation R-values than required by most

local building codes. An R-value is the

ability of a material to resist heat transfer,

and the lower the value, the faster the heat

loss. For example, a typical house in New

York might have insulation of R-11 in the

exterior walls and R-19 in the ceiling,

while the floors and foundation walls may

not be insulated. Asimilar, but well-

designed and constructed house will have

insulation levels that range from R-20 to

R-30 in the walls and from R-50 to R-70 in

the ceilings. Carefully applied fiberglass

batt or rolls, wet-spray cellulose, or foam

insulation will fill wall cavities completely.

Foundation walls and slabs should be as

well insulated as the living space walls.

Poorly insulated foundations have a nega-

tive impact on home energy use and com-

fort, especially if the family uses the lower

parts of the house as a living space. Also,

appliances—such as domestic hot water

heaters, washers, dryers, and freezers—

that supply heat as a byproduct are often

located in the basement. By carefully insu-

lating the foundation walls and floor of

the basement, these appliances can assist

in heating the house.

While most new houses have good insula-

tion levels, it is often poorly installed. In

general, gaps and compaction of insula-

tion reduce its effectiveness.

Air/Vapor Retarders

Water vapor condensation is a major

threat to the structure of a house, no mat-

ter what the climate. In cold climates,

pressure differences can drive warm,

moist indoor air into exterior walls and

Foundation walls

and slabs should be as

well insulated as the

living space walls.

Workers install a structural insulated panel.

Photo by Craig Miller Productions, NREL/PIX02452

attics. The air condenses as it cools. The

same can be said for southern climates,

just in reverse. As the humid outdoor air

enters the walls and encounters cooler

wall cavities, it condenses into liquid

water. This is the main reason why some

buildings in the South have problems with

mold and rotten wood after they’re retro-

fitted with air conditioners.

Avapor retarder is a material or structural

element that can be used to inhibit the

movement of water vapor, while an air

retarder can inhibit airflow, into and out of

a house’s envelope. How to design and

install vapor retarders depends a great

deal on the climate and on the chosen con-

struction method. However, any water

vapor that does manage to get into the

walls 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 and

sound construction practices. Systems that

control air and water vapor movement in

homes rely on the nearly airtight installa-

tion of sheet materials on the interior as

the main barrier.

The Airtight Drywall Approach (ADA)

uses the drywall already being installed

along with gaskets and caulking to create a

continuous air retarder. In addition, seams

where foundation, sill plate, floor joist

header, and subfloor meet are also care-

fully sealed with appropriate caulk or gas-

ket material.

Consult your local building codes official

on the best vapor retarder method to use

in your area.

Windows

The typical home loses more than 25 per-

cent of its heat through windows. Even

modern windows insulate less than a wall.

Therefore, an energy-efficient house in a

heating-dominated climate should, in gen-

eral, have few windows on its northern,

eastern, and western sides. Total window

area should also not exceed 8 to 9 percent

of the floor area for those rooms, unless

the designer is experienced in passive

solar techniques. If this is the case, then

increasing window area on the southern

side of the house to about 12 percent of

the floor area is recommended. This is

often called solar tempering.

Aproperly designed roof overhang for

south-facing windows will help prevent

overheating in the summer. North, east,

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 south

facing windows.

Photo by Sara Farrar, NREL/PIX08155

and west windows should have low Solar

Heat Gain Coefficients (SHGC). South

windows with properly sized overhangs

should have a high SHGC to allow winter

sun (and heat) to enter the house. The

overhang blocks the high summer sun

(and heat). If properly sized overhangs are

not 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 as

those produced 10 years ago, according to

regional, climatic guidelines (note: houses

with any kind of solar tempering have

other guidelines). The best windows are

awning and casement styles because these

often close tighter than sliding types. In all

climates, window glass facing south with-

out overhangs can cause a problem on the

cooling side that far exceeds the benefit

from the winter solar gains.

Weatherstripping and Caulking

You should seal air leaks everywhere in a

home’s thermal envelope to reduce energy

loss. Good air sealing alone may reduce

utility costs by as much as 50 percent

when compared to other houses of the

same type and age. You can accomplish

most air sealing by using two materials:

caulking and weatherstripping. Caulking

can be used to seal areas of potential air

leakage into or out of a house. And weath-

erstripping can be used to seal gaps

around windows and exterior doors.

Controlled Ventilation

Since an energy-efficient house is tightly

sealed, it needs to be ventilated in a con-

trolled manner. Controlled, mechanical

ventilation prevents health risks from

indoor air pollution, promotes a more

comfortable atmosphere, and reduces air

moisture infiltration, thus reducing the

likelihood of structural damage.

Furnaces, water heaters, clothes dryers,

and bathroom and kitchen exhaust fans

expel air from the house, making it easier

to depressurize an airtight house if all else

is ignored. But natural-draft appliances

may be back-drafted by exhaust fans,

which can lead to a lethal buildup of toxic

Good air sealing alone

may reduce utility

costs by as much as

50 percent.

Air leakage can occur in many places throughout a home.

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basement wall

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entrance for

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Joints

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gases in the house. For this reason, sealed-

combustion heating appliances, which use

only outside air for combustion and vent

combustion gases directly to the outdoors,

are very important for ventilation energy

efficiency and safety.

Heat recovery ventilators (HRV) or energy

recovery ventilators (ERV) are growing in

use for controlled ventilation in airtight

homes. These ventilators can salvage

about 70 percent of the energy from the

stale exhaust air and transfer that energy

to the fresh air entering by way of a heat

exchanger inside the device. They can be

attached to the central forced air system or

may have their own duct system.

Other ventilation devices, such as

through-the-wall or “trickle” vents, may

be used in conjunction with an exhaust

fan. They are, however, more expensive to

operate and possibly more uncomfortable

to use because they have no energy recov-

ery features to precondition the incoming

air. Uncomfortable incoming air can be a

serious problem in northern climates and

can create moisture problems in humid cli-

mates. Therefore, this ventilation strategy

is only for arid climates. Other systems

pull outside air in with a small outside

duct on the return side of the furnace.

Heating and Cooling Systems

Specifying the correct sizes for heating and

cooling systems in airtight, energy-efficient

homes can be tricky. Rule-of-thumb sizing

is often inaccurate, resulting in wasteful

operation. Conscientious builders and

heating, ventilation, and air-conditioning

contractors size heating and cooling

equipment based on careful consideration

of the thermal envelope characteristics.

Generally, energy-efficient homes require

relatively small heating systems, typically

less than 50,000 Btu/hour even for very

cold climates. Some require nothing more

than sunshine as the primary source of

heat along with auxiliary heat from radi-

ant in-floor heating, a standard gas-fired

water heater, a small boiler, a furnace, or

electric heat pump. Any common appli-

ance that gives off “waste” heat can also

contribute significantly to the heating

requirements for such houses.

If an air conditioner is required, it’s often a

small unit and sufficient for all but the

warmest climates. Sometimes only a large

fan and the cooler evening air are needed

to make the house comfortable. The house

is closed up in the morning and stays cool

until the next evening.

Smaller-capacity heating and cooling sys-

tems are usually less expensive to buy and

operate. This helps recover the costs of

purchasing more insulation, and other

energy-efficient products, such as win-

dows and appliances. Always look for the

EnergyGuide label on heating and cooling

equipment. The label will rate how effi-

cient it is as compared to others available

on the market.

In climates where summer cooling require-

ments dominate, light-colored materials

and coatings (paint) on the exterior siding

and roof can help reduce cooling require-

ments by up to 15 percent. Carefully

selected and placed vegetation in any cli-

mate also contributes to reduced cooling

and heating loads.

Generally, energy-

efficient homes

require relatively

small heating systems.

Heat recovery ventilation.

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air inlet

Air-to-air

heat exchanger

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air return

Fresh air

supply

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air

Energy-Efficient Appliances

Appliances with relatively high operating

efficiencies are usually more expensive to

purchase. However, higher efficiency

appliances provide a measure of insurance

against increases in energy prices, emit

less air pollution, and are attractive selling

points when the home is resold.

Home buyers should invest in high-effi-

ciency appliances—such as water heaters,

clothes washers and dryers, dishwashers,

and refrigerators—especially if these

appliances will be used a great deal.

Because all major appliances must have an

EnergyGuide label, read the label carefully

to make sure you buy the most efficient

appliance. To help you choose wisely,

major appliances with an Energy Star

label exceed the federal government’s

minimum efficiency standards by a large

percentage.

Energy-efficient lighting helps keep

energy bills down by producing less heat

and reducing cooling requirements. Fluo-

rescent lighting, both conventional tube

and 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 many

advantages. They feel more comfortable

because the additional insulation keeps

the interior wall at a more comfortable

and stable temperature. The indoor

humidity is also better controlled, and

drafts are reduced. Atightly sealed

air/vapor retarder reduces the likelihood

of moisture and air seeping through the

walls. They are also very quiet because the

extra insulation and tight construction

helps to keep exterior noise out better.

But these houses also have some potential

disadvantages. They may cost more and

take longer to build than a conventional

home if there’s a lack of builder familiarity

with new construction techniques and

products available on the market. Even

though the house’s structure may differ

only slightly from conventional homes,

the builder and contractors may be

unwilling to deviate from what they’ve

always done before. They may need more

training if they have no experience with

these 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 the

house. There are energy-related computer

software programs that can help with

these evaluations. The design should

accommodate appropriate insulation lev-

els, moisture dynamics, and aesthetics.

Decisions regarding appropriate win-

dows, doors, and heating, cooling and

ventilating appliances are central to an

efficient design. Also the cost, ease of con-

struction, the builder’s limitations, and

local building code compliance should be

competently evaluated. Some plans are

relatively 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 government’s

Building America and Energy Star

Homes programs, as well as local home

energy rating programs, all of which pro-

mote the construction of energy-efficient

houses. Many of these builders construct

energy-efficient homes to differentiate

themselves from their competitors. Con-

struction costs can vary significantly

depending on the materials, construction

techniques, contractor profit margin, expe-

rience, and the type of heating, cooling,

and ventilation system chosen.

Because energy-efficient homes require

less money to operate, many lenders now

offer energy-efficient mortgages (EEMs).

EEMs typically have lower points and

allow for the stretching of debt-to-income

ratios. State and local government energy

offices can be contacted for information on

region-specific financing.

In the end, your energy-efficient house

will provide you with superior comfort

and lower operating costs, not to mention

a higher real estate market value.

Higher efficiency

appliances provide a

measure of insurance

against energy prices

and emit less air

pollution.

The building site

and its climate should

be carefully evaluated

to determine the

optimum design.

Resources

The following are sources of additional information on

energy-efficient houses:

The Energy Efficiency and Renewable Energy

Clearinghouse (EREC)

P.O. Box 3048

Merrifield, VA22116

1-800-DOE-EREC (1-800-363-3732)

E-mail: [email protected]

Web site: http://www.eren.doe.gov/consumerinfo/

EREC provides free general and technical information to the

public on many topics and technologies pertaining to energy

efficiency and renewable energy.

Organizations

American Solar Energy Society, Inc. (ASES)

2400 Central Avenue, G-1

Boulder, CO 80301

Phone: (303) 443-3130; Fax: (303) 443-3212

E-mail: [email protected]

Web site: http://www.ases.org

Anational advocacy organization dedicated to the use of solar

energy in buildings.

Building America

U.S. Department of Energy

Office of Building Systems, EE-41

1000 Independence Avenue, SW

Washington, D.C. 20585-0121

Web site: http://www.eren.doe.gov/buildings/

building_america/

Works with the home building industry to produce quality

homes that use up to 50 percent less energy without costing

more to build.

Efficient Windows Collaborative

Alliance to Save Energy

1200 18th Street NW, Suite 900

Washington, D.C. 20036

Phone: (202) 857-0666; Fax: (202) 331-9588

E-mail: [email protected]g

Web 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. Environmental

Protection Agency

Phone: (888) STAR-YES (1-888-782-7937)

E-mail: info@energystar.gov

Web site: http://www.energystar.gov/

Provides lists of Energy Star

-qualified products, including

appliances and windows, as well as information on its energy-

efficient homes program.

Lawrence Berkeley National Laboratory

Building Technologies Department

MS 90-3111

Berkeley, CA94720 USA

Phone: (510) 486-6845; Fax: (510) 486-4089

Web site: http://eetd.lbl.gov/btp/btp.html

Provides information on past and current research in buildings

energy efficiency.

National Renewable Energy Laboratory

The Center for Buildings and Thermal Systems

1617 Cole Blvd.

Golden, CO 80401

Web site: http://www.nrel.gov/buildings_thermal

Provides information on energy-efficient buildings.

Oak Ridge National Laboratory (ORNL)

Buildings Technology Center

P.O. Box 2008, MS-6070

Oak Ridge, Tennessee 37831-6070

Phone: (865) 574-5206; Fax Number: (865) 574-5227

Web 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 1000

Washington, DC 20005-4706

Phone: (202) 628-7400; Fax: (202) 393-5043

E-mail: [email protected]

Web site: http://www.sbicouncil.org

Promotes the use of energy-efficient and passive solar building

design and construction.

Web Sites

Building Energy Software Tools

U.S. Department of Energy

Office of Building Technology, State and Community

Programs

Web 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 Database

Lawrence Berkeley National Laboratory

Web site: http://eetd.lbl.gov/coolroof/

Assists with the selection of roofing materials that reflect

instead of absorb the sun’s radiant energy.

Green Buildings

Center of Excellence for Sustainable Development

Web site: http://www.sustainable.doe.gov/buildings/

gbintro.htm

Provides information and links on energy-efficient buildings.

(Continued on page 8)

Continued from page 7

The Residential Energy Efficiency Database

Web site: http://www.its-canada.com/reed/

Provides a wide-range of information on energy-efficient

houses, including house plans.

Zip Code Insulation Database

Oak Ridge National Laboratory

Web 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 information

about energy-efficient home elements. The list is not

exhaustive, nor does the mention of any publication con-

stitute a recommendation or endorsement.

Books, Pamphlets, and Reports

Buildings for a Sustainable America Case Studies, B. Miller,

ASES, 1997. Available from ASES or SBIC (see

Resources).

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, Rocky

Mountain 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 HTML

at 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 for

Residential and Small Commercial Buildings, J. Lstiburek

and 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 from

ASES (see Resources).

Residential Windows: A Guide to New Technology and

Energy 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 of

Energy Efficiency and Renewable Energy, 1997. Avail-

able from ORNLin PDF and HTMLat http://www.ornl.

gov/roofs+walls/insulation/. Print version is available

from EREC (see Resources).

Periodicals

Energy Design Update. Published by Cutter Information

Corporation, 37 Broadway, Arlington, MA02474-5552;

Phone: (800) 964-5118 or (781) 648-8700; Web site: http://

www.cutter.com. This monthly newsletter contains

information 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 a

wide variety of topics.

The Journal of Light Construction. Published by Builder-

burg Partners, Ltd., 932 West Main Street, Richmond, VT

05477; Phone: (800) 375-5981. This monthly journal often

features articles on energy conservation techniques for

the home builder.

Home Energy Magazine. 2124 Kittredge Street, #95,

Berkeley, CA94704; Phone: (510) 524-5405; E-mail:

contact@homeenergy.org,; Web site: http://www.

homeenergy.org/. It’s a source of information on reduc-

ing energy consumption in the home.

Solpan Review. Published by Drawing-Room Graphic

Services, Ltd., P.O. Box 86627, North Vancouver, BC V71

412 , Canada; Phone (604) 689-1841. This bimonthly

newsletter features articles on energy conservation for

the building industry, including information on new

products and energy-efficient practices in residential

construction.