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SOLAR CENTER INFORMATIONNCSU � Box 7401 � Raleigh, NC 27695 � (919) 515-3480 � Toll Free 1-800-33-NC SUN

Harnessing the sun's energy with a passive solardesign can mean substantial savings on utility bills. Allthat extra heat and sunlight can also pose some decorat-ing challenges.

Unless you plan carefully, your decorating schemewill interfere with the efficiency of your passive solardesign, and the heat and sunlight will harm your furnish-ings.

Floors, wall, furniture, fabrics, window treatmentsand accessories � the basic elements in any decoratingplan � need to be thought of in terms of your passivesolar design.

FloorsThe floor of your solar home exposed to the sun is an

important part of the passive design. It acts as a massmaterial, absorbing sunlight, conducting surface heat intoits mass and holding onto that heat.

The best thermal mass materials have dark colored,rough, matte surfaces. They may include concrete, brick,slate, ceramic tile and marble. Concrete, for example,can be stained before it is poured, or it can be patternedand colored to look like brick or slate giving you aneconomical, functional and attractive floor.

Wall to wall carpeting should not be used on athermal mass floor. Area rugs can be used if they arekept small. Remember to turn them so fading and wearwill be even. Navahos, kilims and dhurries "weather"well.

Straw or sisal mats are excellent choices. Theysoften the thermal mass floor, do not fade or interferewith heat flow and can absorb excess humidity.

THE FLOOR is an important element of passive solardesign. Darkly colored, rough, matte surfaces, such as brick,slate, concrete, and ceramic tile make good choices.

Decorating Your Passive Solar Home:Balancing Energy and Aesthetics

Industrial Extension Service College of Engineering

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Carpet and a thermal mass floor combine best in a direct gain system when the two are similar colors. Be careful to leavethe mass floor area uncovered and exposed to the sun.

Your best approach is to keep wood furniture out ofthe direct sunlight. If this is not possible, plan to re-arrange the furniture every month or so by rotatingpieces in and out of the sun to keep the damage to aminimum.

You also need to place furniture so it shades themass floor or wall as little as possible. A general ruleof thumb is to shade less than 30 percent of the massarea. Otherwise, you are interfering with its maximumeffectiveness for heat absorption and release.

Small scale, open back, open arm furniture with noskirt is the best choice. Select occasional pieces ratherthan the stuffed chair or sofa. Keep the window areafree to capture the sunlight. Tall furniture should not beplaced near there.

Do not put a piano or other musical instrument indirect sunlight. The heat and humidity will spoil thesound and the sunlight will craze and crack the finish onthe keys.

Arrange furniture so that no one faces the sundirectly. The glare can be distracting.

FurnitureWhen choosing furniture for your solar home, make

practical choices to withstand the light and heat.Wood furniture will change color when exposed to

sunlight, and the extra heat will dry it out, causingcracking, splitting and loosening of glued joints.

How much will the color change? It depends on thenatural pigments in the wood, how the piece was finishedand the care it has received.

While dark woods will lighten, some of the very lightwoods will actually get darker. Most of the change incolor will occur during the first year. Stains actuallyaccelerate the color change. A different chemical processoccurs and the stain pigment changes rather than thewood pigment.

Proper care will provide some protection. Usefurniture oil or wax to help seal the wood. Avoidproducts that contain alcohol, which accelerate the dryingof the wood.

Solid woods are more likely than veneers to shrink orswell because solid wood is less flexible.

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Heat is another element that affects fiber durablility.The more sunlight the fabric absorbs, the greater thechance that heat will damage the fibers.

Humidity (moisture in the air) can also damagefabrics. The relative humidity in passive solar spaces canbe very high. Fabrics vary in their ability to absorbmoisture.

A fabric's durability is determined by fiber content,yarn construction, type of weave, finish and dye type.

Table 1. Fiber Characteristics and Users

FabricsTo select the proper fabrics when decorating passive

solar spaces, choose ones that can withstand the climateconditions there.

Sunlight has the most visible and devastating effecton fabrics. First the color fades, then the fiber itselfdeteriorates. Very few fibers are resistant to the sun'sdestruction.

Generic Sunlight Resistance Heat Resistance Absorbency Tensile UseFiber Strength

Acetate Slight loss of strength, Little degradation Low Low Notlittle color loss recommended

Acrylic Very little loss of strength, Little degradation Low Medium Windows,no discoloration Upholstery,

Carpeting

Cotton Gradual loss of strength, Excellent resistance Medium Medium Upholsterygradual yellowing to degradation by heat

Glass None None None None Windows

Leather No loss of strength, Embrittlement, Low High Upholsteryslight discoloring stabilized by care

Linen Gradual loss of strength Discolors at high High High Upholsterytemperatures

Modacrylic Very little loss of strength Little degradation Low Medium Windows

Nylon Gradual loss of strength, Little degradation Low High Windowslittle color loss

Olefin Moderate strength loss, Moderate None Medium Notgradual embrittlement, decomposition, recommendedcan be stabilized embrittlement

Polyester Very gradual strength loss, Little discoloration Low Medium Windows,no discoloration Upholstery

Rayon Gradual loss of strength, Little degradation High Low Notaffected more than cotton recommended

Silk Moderate loss of strength, Less affected Medium High Upholsteryaffected more than cotton, than wooldepends on dye and additives

Vinyl No loss of strength, Gradual None High Upholsteryslight discoloration embrittlement

Wool Loss of strength, Loses softness from High Low Upholstery,gradual fading prolonged exposure Carpeting

Source: Fabrics for the Energy-Concious Home, Michigan State University, Extension Bulletin E-1772, July, 1984

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Generally, synthetic fibers are more resistant to sunlightthan natural fibers. But natural fibers like cotton, linen,ramie and rayon absorb moisture readily. Nylon andpolyester absorb very little, and olefins absorb little or nomoisture at all. Too much absorption can cause fabricslike rayon to sag or lose their shape. Moisture can alsocarry airborne pollutants and contaminants into thefabric, speeding its deterioration.

Tightly woven weaves are generally more resistant todamage from the sun. If both the yarns and the weaveare uniform and even, the fabric will be even moreresistant. When the yarns or weave are made in a thickpattern, the fabric will weaken and deteriorate in thosethin areas.

Some dyes are more resistant to fading than others.Solution dyeing, used only on synthetic fibers, givesexcellent results. The dye is added to fiber-formingliquid solution before it is forced through the spinneret toform filaments. This means the color is distributedthroughout the entire fiber.

Vat-dyeing refers to a particular class of dye that,when properly applied, gives good colorfastness. Vatdyes are most often used on cotton or polyester cottonblends.

Colorfastness varies among classes of dyes. Reliablemanufacturers choose dyeing methods based on the fiberand the fabric's intended use. Since you, as a consumer,cannot determine what class of dye was used, selectfabric manufactured specifically for your intended use.

The fabric in your window treatments will be mostvulnerable to the effects of light, heat and moisture.Look for a sturdy fabric that offers some insulation andthat reflectss light and heat. Also consider the amount ofmoisture the fiber can absorb and its ability to resistindoor air pollution. Check Table 1 for suggestions forwindow coverings. Select a fiber that offers the greatestresistance to the severest of the elements to which it willbe exposed in your solar space.

Remember that a drapery made from a fairlyresistant fabric with a reflective lining will last longerthan an excellent sun-resistant but unlined fabric.

Table 1 can also be used when choosing upholsteryfabrics for solar interiors, but keep in mind the fact thatthe furniture will be subject to wear and tear caused bypeople as well as to the sunlight.

Almost any color will fade to some degree. Lookfor the term "sun-resistant" on the label of fabrics youchoose. It indicates that the dye resists fading. But it isnot a guarantee against fading unless stated. If fadingwill be a problem, choose light to medium neutral orearth colors, because they do not show fading as quicklyas bright, vivid colors. Light colors also reflect heatmore than dark colors, and heat absorption increasesfabric deterioration.

AccessoriesAccessories are also subject to damage from

exposure to the sun. A solar space is not the best placeto show off your art collection. Sunlight can crack oilpigments, fade watercolors and deteriorate paper andcanvas in a very short time. Acrylics are more resistantbut are still not recommended in areas of direct expo-sure.

Colors on objects can fade. Some finishes onceramic lamps, ashtrays, etc., may craze, then crack,after prolonged exposure to the sun. If you mustfurnish your solar space as a living space, then plan torotate the accessories (and furniture) in shaded areaswith items in unshaded areas. Also, move accessoriesevery few weeks so that the exposure does not createdark spots on the furniture underneath the accessories.

Use inexpensive pillows, baskets and posters toaccessorize sun-filled spaces. As a result, your loss willnot be as costly.

Although the sun damages some forms of art, itenhances others. A stained glass design can give bright,non-fading color to the space. A few plants, strategi-cally placed according to light requirements, can addsoftness and interest to the area.

OUTDOOR FURNITURE, such as this glass top table withvinyl cushioned chairs, is a good choice for sunspace areas.It produces minimal shading and can withstand heat,humidity and sunlight.

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CONCRETE Trombe walls can be painted the same coloras other walls in the room, making them more attractive.

ARRANGE FURNITURE in the room so that it does notblock the Trombe wall. Keep wall decorations to a mini-mum.

Special ProblemsCertain passive solar systems present special decorat-

ing and furnishing challenges. Let's look at specificguidelines for direct-gain, indirect-gain (Trombe wall)and isolated gain (greenhouse or sunspace) systems.

Direct-gain SystemThe direct-gain system affects your interior decorat-

ing plan more than any other system since the livingspace itself is the collector. Effects of the sun on fabricsand furniture must be your major consideration.

Try to keep conversation groupings and dining areassix to eight feet from the glass area and arrange furnitureso no one faces the sun directly. Use light colors, mattefinishes and smooth textures to cut down on visualdiscomfort and glare.

If the floor is thermal mass, do not use bulky,overstuffed furniture with skirts, and do not bring wall-to-wall carpet out to the south glass wall. Small arearugs will not intefere with the solar collection and stor-age. You can also change to a thermal mass flooringmaterial without disturbing your decorating. Just keepthe color of the two materials similar.

Window insulation is a must in a direct-gain solarsystem. Heat gained during the day is easily lost at nightwithout it. A window treatment with edge seals, vaporbarrier and heat resistant or a reflective surface (to reflectsummer sun) is necessary. Interior window treatmentsare not as effective for reducing heat gain in the summeras is exterior shading.

Indirect-gain (Trombe Wall)When Trome walls are used to collect and store heat,

nothing should block the path. Solid or overstuffedfurniture will obstruct the radiant heat coming from theTrombe wall while one or two pieces with open backsand legs (side chair or an etagere) will not.

Oil paintings, watercolors and other fine art shouldnot be hung on a Trombe wall. The warm surface willdry out the painting, encouraging fading and deteriora-tion.

When half Trombe walls are used, window insula-tion is a must at night to keep from losing the heat gainedduring the day.

6SC 100 June 2000

For More Information

The North Carolina Solar Center has other free fact sheets and information on solar energy, renewable energy, energy efficiency, andrelated subjects. For more information on these topics or to learn about the resources available, contact the Solar Center.

Prepared by: Dr. Wilma Hammett, Extension Interior Design Specialist, NC Cooperative Extension Service, NC State University

Isolated-gain (Greenhouse or Sunspace)The sunspace or greenhouse should be furnished as a

porch or sun room. Wicker or open-mesh porch furniturecan withstand direct sunlight and the high heat andhumidity. Glass-topped tables will allow sunlight to reachthe thermal mass floor. This is not the place for fine woodor upholstered furniture. (Note picture, page 4.)

Keep the floor uncovered, or use an open weave sisalor rush rug that won't interfere with the heat flow.

Window insulation is not critical for the sunspace orgreenhouse since the space itself can be closed from thehome's living space.

In conclusion, make sure the decorating and furnish-ing of your passive solar interior does not interfere withthe efficiency of the system. Select furnishings that willperform well in the environment of the passive solarinterior. Sunlight, heat and humidity will be hard on yourfurnishings. Choose wisely when furnishing your interiorand you'll save more than energy dollars.

Sponsored by the Energy Division, NC Department of Commerce, and the US Department of Energy, with State Energy Program funds, in cooperationwith North Carolina State University. However, any opinions, findings, conclusions, or recommendations expressed herein are those of the author(s)and do not necessarily reflect the views of the Energy Division, NC Department of Commerce, or the US Department of Energy.

ReferencesThe following publications provide further informa-

tion on decorating your passive solar home. This list isnot exhaustive; inclusion does not imply endorsement bythe North Carolina Solar Center, nor does omission ofsimiliar materials imply criticism.

Breen, Jill C. Interior Design for Passive Solar Homes. National Renewable Energy Laboratory, Golden, Colorado.Cole, John N. "Sunlight's Special Effects." Rodale's New Shelter, November/December, 1981.Fridgen, C.C. and D.A. Guerin. Energy-Conscious Interior Design. Michigan State University, Extension Bulletin E-1771, July, 1984.Fridgen, C.C. and D.A. Guerin. Fabrics for the Energy- Conscious Home. Michigan State University, Extension Bulletin E-1772, July, 1984.Harden, Tracey. "Decorating the Solar Home." Building Manual, Spring, 1982.Hurst, Homer T. Vinyl Floor Products for Passive Solar Environments, Research Report, August, 1982.Kinnaird, Bruce. "Gone with the Sun." Rodale's New Shelter, January, 1983.

North Carolina Solar CenterBox 7401, NCSU, Raleigh, NC 27695-7401Phone: (919) 515-3480 Fax: (919) 515-5778Toll-Free in NC: 1-800-33 NC SUNEmail: ncsun@ncsu.eduWeb: www.ncsc.ncsu.edu

Energy Division, NC Department of Commerce1830A Tillery Place, Raleigh, NC 27604Phone: (919) 733-2230 Fax: (919) 733-2953Toll-free: 1-800-622-7131E-mail: ncenergy@energy.commerce.state.nc.usWeb: www.energy.state.nc.us/

Grateful appreciation is expressed to Deck House Inc., Chapel Hill, for use of the photographs on page 2.

Printed on recycled paper

3,000 copies of this public document were printed at a cost of $531.06 or $.18 per copy.