The Sun-Tempered Superinsulated House Fact Sheet No. 9.936 Consumer Series|Housing by K.R. Tremblay, Jr.* One result of rising energy costs is the • Attached garage or unheated storage areas Quick Facts evolution of energy-efficient house designs are located on the north and west. based on two distinct concepts: passive solar This floor plan fits well with a landscape • A sun-tempered, and superinsulation. Passive solar emphasizes plan that has outside activity areas (patios superinsulated house com­ orienting the house to the sun. Super­ and decks) on the south side of the house. bines passive solar and insulation emphasizes improving the thermal Patios and decks can be used more of the year super-insulation. efficiency of the structure. because of their sunny, protected location. • It features solar orientation, Both concepts involve greater integration Solar orientation also relies on proper of the house with its climatic environment, win­dow placement. The STS house increased insulation, use of improved construc­tion materials, minimizes win­dow openings in order to effective air/vapor barriers, and appropriate construction methods. reduce energy use. Generally, window area controlled ventilation­ and Depending on the climate of an area, one should be no more than 8 percent of the improved windows. approach is favored over the other. total floor area. Locate as many windows as • Design is flexible and fits a For Colorado, with its cold but sunny possible on the south side of the house. This variety of architectural­ styles. climate, the sun-tempered superinsulated provides solar heat as well as light to create a (STS) house, which combines both concepts, comfortable, well-lit environment. • It does not require attention is an appro­priate design. Elements in the STS To prevent overheating in the summer, for its operation, but is house include: shade the south windows by a roof overhang. automatically­ controlled and • solar orientation, A roof overhang of about 2 feet adequately self-regulating.­ • increased insulation levels, shades an 8-foot wall. While south facing • an effective air/vapor barrier, win­dows are encouraged, the STS house is a • Over its life, considerable • controlled ventilation, and flexible design in that windows can be placed savings in monthly operating • improved windows. as needed. However, the overriding principle costs will result. favors south-oriented window placement. Solar Orientation Colorado’s excellent solar environment Increased Insulation Levels can be effectively used in the STS house as The STS house achieves increased a source of supplemental heat. This requires insulation levels without making the opening the house to the south through construction method overly costly or room orientation and window placement. complex. The main departure from The STS house is designed around a floor conventional techniques­ is in wall con­ plan like that shown in Figure 1. The key struction. The wall is framed with 2 inch principles are: by 6 inch studs placed on 24-inch centers. • Rooms most frequently occupied This allows placement of a standard 6-inch (living room and family room) face insulating batt with an R-19 rating. A layer of south to make the most effective use of rigid insulation is applied over the exterior solar energy. wall framework. • Storage rooms, utility rooms, bathrooms, The rigid insulation serves several bedrooms and other less fre­quently important purposes: occupied rooms are located on the north • It increases the R rating of the wall. and west to serve as a thermal buffer. • It reduces thermal bridging whereby heat © Colorado State University is con­ducted through the studs. Extension. 6/94. Revised 3/14. • It forms a contin­uous blanket around www.ext.colostate.edu the house exterior, thus reducing­ *K.R. Tremblay, Jr., Extension specialist and professor, air infiltration. design and merchandising. Originally written by L. R. Walker. 3/2014 Rigid insulation gaskets. Caulk holes in the plates for wiring should be 1 inch thick runs. Also seal plumbing penetrations in in homes at lower the ceiling. elevations or 2 inches The advantage of ADA is that it uses thick for homes in conventional construction techniques and mountainous loca­ materials. It requires extra care for detail tions. This provides and some construction rescheduling, in an R-25 to R-30 wall that the exterior drywall is put in place for the STS house. before the interior walls are installed. By Apply either siding or a having the air/vapor barrier visible, minor stucco-like finish­ over problems are easily detected and repaired. the rigid insulation. Figure 2 illustrates the wall construction. Controlled Ventilation Figure 1: Floor plan for an STS house. Ceilings in the Since the STS house is well sealed, STS house are insulated to R-40. This can controlled ventilation is necessary to be done with conventional roof framing prevent indoor air pol­lution problems. The trusses and 12 inches of loose fill insu­lation. recommended rate of air exchange in a Foundation walls are insulated to R-20 house is 0.5 air changes per hour (ACH). down to the frostline and to R-10 below the This means that one-half of the volume of frostline to the footing. One easy method air in the house is changed every hour. In for insulating foun­dation walls is to apply conven­tional houses, this recommended rigid insulation to the outside of the wall. rate is easily met (and often exceeded) The concrete slab in a basement­ should through air infiltration. In the STS house have R-5 insulation (achieved with 1 inch of using the airtight drywall approach rigid insulation) beneath it. Rigid insula­tion to sealing the structure, the rate of air in contact with the ground must be able exchange can be as low as 0.1 ACH. At such to withstand moisture contact. Extruded a low rate, indoor air pollution caused by polysty­rene is suitable for this purpose. cigarette smoke, radon gas, formaldehyde gas, combustion gases from stoves and heating systems, and cook­ing odors can be Air/Vapor Barrier a health problem. An effective air/vapor barrier is an The STS house uses an air-to-air heat important feature. Studies show that in ex­changer to control the ventilation rate well insulated houses, air infiltration can at 0.5 ACH and thus maintains adequate account for up to 40 percent of the heat indoor air quality. An air-to-air heat lost. Also, moisture must be kept out of wall exchanger is slightly larger than a window cavities to prevent deterioration of framing air conditioner. The unit is connected­ members. The perfect air/vapor barrier is through ducts to all rooms in the house. Figure 2: Wall construction in the STS house (use a combination of these an impervious membrane installed on the Two continuously running small capacity diagrams). inside of the exterior-facing surfaces with (80 to 300 cubic feet per minute) blowers no breaks. In the STS house, the air-tight expel stale house air to the outdoors, bring drywall approach (ADA) is used to produce in an equal amount of fresh air, and transfer an effective air/vapor barrier. the heat in the outgoing warm air to the The principle of ADA is to apply drywall incoming cold air (see Figure 4). About 70 in a continuous layer on the interior walls percent of the heat contained in the out­ and ceilings. Use compressible gaskets to going air is recycled by the heat exchanger. seal the tops and bottoms of the walls and Preheated fresh air is supplied to any joints between plates, rim joist, and bedrooms, the living room, and family subfloor or foundation. Note the placement room. Stale air is removed from kitchen, of gaskets in Figure­ 2. bathrooms, and laundry areas. Locate Install the drywall as closely as possible both supply and exhaust vents in or near to window and door openings, and caulk the ceiling of each room. Undercut doors the gap (see Figure 3). Tape the drywall about 1 inch to provide circu­lation between and finish and paint it in the usual manner. rooms when doors are closed. In addition A primer coat of vapor barrier paint will to continuous low speed operation, enhance the air- and vapor-tight seal. Keep blow­ers are controlled by variable speed electrical wiring out of the outside walls control switches located in the kitchen and Figure 3: Sealing window openings using as much as possible. Seal any electrical bathrooms to provide increased ventilation the ADA method. boxes installed in the outside walls with rates when cooking or after showering. Ventilation also includes the type of moisture. “Low E” coatings allow visible heating system installed. In the STS house, light and solar energy into the house, but electricity, natural gas, or propane can be greatly reduce heat radiation through the used for supplemental heating. Electric glass. Thus, heat flowing out of the house heat can be supplied by baseboard units in winter or into the house in summer or radiant panels. Natural gas or propane is reduced. heaters must be chosen with greater care The R-value for a double pane, “low E” since they require air for combustion. In coated window is 3.1 for coated glass and a conventional house, this air is supplied 4.3 for a coating on a suspended plastic through infiltration. However, in the STS film. This represents a reduction of heat house where infiltration is minimized, a loss of 40 to 50 percent over a con­ventional dif­ferent method must be used. double paned window. “Low E” glass has A preferred method is a sealed combus­ the following additional advantages: tion unit heater. These heaters have • greater occupant comfort due to low rated output (15,000 to 35,000 Btu/ warmer glass surfaces, hour) to match the small heating needs • reduced condensation, and of the STS house. They are space heaters • reduced fabric fading from ultraviolet mounted on outside walls. Combustion light. Figure 4: An air-to-air heat exchanger. air is drawn directly from the outside (see In colder parts of the state, insulating Figure 5). Using space heaters eliminates shutters or shades can be added to the the cost of a distribution network in the windows to further increase their effective house. Due to the well-insulated­ structure R value. and air movement created by the air-to- air heat exchanger, even tempera­tures are maintained throughout the STS Living With an STS House house when using space heaters. Sealed The STS house combines the latest combustion water heaters also are used building materials and construction in the house. techniques with effec­tive use of the solar environment. The design of the STS house is flexible. It can be built in a variety of Improved Windows architectural styles. The five elements Windows represent the weakest energy mentioned above can be applied with defense in any house. Double-paned great flexi­bility in order to accommodate windows have, at best, an R-2 rating. a particular site or the preferences of The STS house uses several methods to the owner. strengthen this weak point. The STS house is comfortable for the Keep windows to a minimum. Avoid occu­pants. Such a well-sealed, heavily- locating windows on the north and west insulated house shields residents from walls as much as possible. The window area outside noise, provides even temperatures should not exceed 8 percent of the floor and humidity levels, and minimizes­ drafts. area of the house. This will provide enough The controlled ventilation ensures excellent windows for light and ventilation and avoid indoor air quality. The solar orientation Figure 5: Sealed combustion unit heater. a closed-in feeling. Window frames are provides a link to the natural environment, made from solid wood, vinyl-clad wood, which is a psychological boost for or metal with a thermal break. Thus, heat the occupants. losses through the frame are reduced. Finally, the STS house does not require The operable windows in the house are spe­cial attention by the occupants for casement or awning types because they its operation. Automatic controls on the create a better seal when closed. heating and ventilation system and built-in All windows are double paned and design features allow the house to be treated with “low E” (low emissivity) self-regulating. coatings. “Low E” coatings are made from Economic considerations are one of a metal oxide deposited in a thin layer the most favorable aspects of living with on the glass or a suspended plastic film an STS house. Over the life of the house, a between the two panes. The coating must considerable savings in monthly operat­ing be on the inside of the sealed window unit costs will result. These savings will quickly in order to protect it from degradation by pay for the added costs of the energy efficient fea­tures incorporated into the house. Such features will add 5 percent to 8 percent to the cost of the house. A final economic advantage of the STS house to a prospective buyer is the economics of the mortgage. Some lenders will allow a higher mortgage loan limit because of the low annual energy operating costs. Thus, the STS house may be open to more potential home buyers.

Sources Amann, J.T., Wilson, A., & Ackerly, K. (2007). Consumer guide to home energy savings. Gabriola Island, Canada: New Society Publishers. Consumer Reports. (2006). Reducing energy costs. Washington, DC: Consumers Union. Energy Star, www.energystar.gov U.S. Department of Energy, www.energy. gov/energyefficiency/buildings.htm Xcel, www.xcelenergy.com/residential/ saveenergy_money

Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. CSU Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.