Ceilings and Attics: Install Insulation and Provide Ventilation
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T e c h n o l o g y F a c t S h e e t CEILINGS AND ATTICS Foil-faced batt insulation is often used in bottom plate, seal penetrations through the For more information, contact: CEILINGS AND ATTICS cathedral ceilings because it has a 0.5 perm drywall, etc.). The open joist ends below the Energy Efficiency and rating and provides the permeability often knee wall should be plugged with squares of Install Insulation and Provide Ventilation Renewable Energy required for use in ceilings without attic cardboard, metal flashing, or rigid insulation; Clearinghouse (EREC) 1-800-DOE-3732 spaces. A vent baffle should be installed be- cellulose insulation blown at a high density; or BENEFITS OF CEILING INSULATION www.eren.doe.gov tween the insulation and roof decking to ensure batt insulation stuffed into plastic bags. The Insulating ceilings is one of the most ATTIC VENTILATION that the ventilation channel is maintained. plugs should be sealed to the joists using Or visit the BTS Web site at cost-effective energy efficiency measures. In Continuous ridge and soffit www.eren.doe.gov/buildings caulk or spray foam. If roof framing provides insufficient space for addition to reducing heat loss in the winter and vents form an effective attic Or refer to the Builder’s Guide required insulation, higher insulation values can The knee wall and attic floor in the attic space heat gains in the summer, ceiling insulation ventilation system. Ridge vent Energy Efficient Building be obtained by either attaching furring strips to behind it should be insulated to recommended improves comfort by bringing ceiling tempera- Association, Inc. the underside of the rafters (that permit addi- levels. The same techniques for achieving Buildings for 651-268-7585 tures closer to room temperatures and provid- tional insulation to be installed), using higher insulation levels in cathedral ceilings the 21st Century www.eeba.org ing an even temperature distribution through- high-density batts (high-density R-30 batts are can be applied to knee walls. Twine is often Buildings that are more out the house. Written and prepared for about the same thickness as R-25 batts and fit used to hold the batt insulation in place. The energy-efficient, comfortable, the U.S. Department of When planning and managing ceiling insula- Soffit into 2x10 framing), or adding rigid foam insula- technique of adding rigid foam insulation over and affordable…that’s the vent Energy by: tion projects, make sure tion under the rafters. Rigid foam insulation the framing is particularly effective. Rigid insu- goal of DOE’s Office of Building Southface Energy Institute offers a resistance to thermal bridging through lation can be notched to fit over the floor joists. Technology, State and • Ceiling is properly sealed 404-872-3549 www.southface.org wood rafters. Rigid foam insulation must be Sealing rigid insulation to floor joists effec- Community Programs (BTS). • Correct insulation levels are selected covered with a fire-rated material when used on tively blocks open floor joists. To accelerate the development Oak Ridge • Insulation is properly installed the interior of a building. Half-inch drywall and wide application of energy the research results are available and accepted, National Laboratory A better approach is to insulate and air seal the efficiency measures, BTS: • Insulation coverage is continuous and builders should follow local code requirements, Buildings Technology Center usually complies, but check with local building rafter space along the sloping ceiling of the knee complete which usually dictate attic ventilation. 423-574-5178 codes for confirmation. wall attic space. The rafters should receive rec- • Conducts R&D on technolo- www.ornl.gov/ORNL/BTC • Attic ventilation is maintained ommended insulation levels. They should be gies and concepts for energy A combination of continuous ridge vent along efficiency, working closely KNEE WALLS covered with a sealed air barrier, such as drywall Attic floors over flat ceilings are often the easiest the peak of the roof and continuous soffit with the building industry The Model Energy Code Knee walls are vertical walls with attic space or foil-faced hardboard. The barrier must be part of an exterior building envelope to insulate. vents at the eaves provides the most effective can be obtained from the and with manufacturers of directly behind them. They are often found in caulked to the top plate of the exterior wall They are usually accessible and have ample ventilation. A rule of thumb is to use 1 sq. ft. of International Code Council by materials, equipment, and houses with finished attics and dormer win- below the attic space and to the top plate of the room for insulation. However, many homes use net vent opening for every 150 sq. ft. of insu- calling 703-931-4533 appliances dows, such as in story-and-a-half designs. knee wall itself. All other cracks and holes must cathedral ceilings or have attic knee walls that lated ceiling or 1:300 if the insulation has a MECcheck, a companion • Promotes energy/money One approach to constructing an energy-effi- be sealed as well. One advantage of this tech- present unique insulation requirements. vapor barrier. Vent area should be divided compliance software saving opportunities to both package, can be ordered from cient knee wall is to first air seal the knee wall nique is that any ductwork located in this space equally between the ridge and soffits. builders and buyers of homes DOE by calling using conventional techniques (i.e., seal the is now inside the conditioned space. ATTIC VENTILATION Cap vents and gable vents can supplement a 1-800-270-CODE and commercial buildings Most building codes require roof vents to expel roof design that has insufficient ridge vent or downloaded directly • Works with State and local moisture that could cause insulation or other from the Web at regulatory groups to improve area. Turbine vents can also be used, although www.energycodes.org/ ATTIC KNEE WALL DESIGN building materials to deteriorate during winter. building codes, appliance they require annual maintenance. Electrically resid/resid.htm. In summer, ventilation may reduce roof tem- Knee wall standards, and guidelines for powered roof ventilators are not recommended peratures, thus lengthening a roof’s life. NOTICE: Neither the United Desired efficient energy use because they consume more energy than they ventilation States government nor any • Provides support and grants However, researchers are investigating whether save. Powered vents can also remove condi- agency thereof, nor any of their Attic Seal living Seal attic ventilation is beneficial for all climates. For tioned air from a home through ceiling leaks employees, makes any warranty, outlet to States and communities space express or implied, or assumes box to Attic space years, researchers have believed the cooling and bypasses, pull pollutants from the drywall Hardboard for deployment of energy- any legal liability or responsibility efficient technologies and benefits of ventilating a well-insulated attic are crawlspace into a home, and cause exhaust for the accuracy, completeness, Seal all edges of rigid Seal or usefulness of any information, foam insulation practices negligible. Some experts also question whether gases from fireplaces and combustion appli- apparatus, product, or process Unwanted air leakage Attic ventilation ventilation effectively removes moisture. Until ances to enter a home. disclosed. The views and opin- ions of authors expressed herein do not necessarily state or reflect Printed with a renewable-source ink on paper containing at those of the United States gov- least 50% wastepaper, including 20% postconsumer waste. OFFICE OF BUILDING TECHNOLOGY, STATE AND COMMUNITY PROGRAMS ernment or any agency thereof. February 2000 DOE/GO-102000-771 ENERGY EFFICIENCY AND RENEWABLE ENERGY • U.S. DEPARTMENT OF ENERGY CEILINGS AND ATTICS ATTIC INSULATION TECHNIQUES at the soffit, porch, garage, and attic access to prevent the ATTIC EAVES Loose-fill or batt insulation is typically installed in an attic. insulation from spilling. Although installation costs may vary, blowing loose-fill attic 2. Follow the manufacturer’s specifications (number of bags Batt Additional or raised top plate insulation—fiberglass, rock wool, or cellulose—is usually less insulation per square feet) to obtain complete coverage of the blown Soffit dam expensive than installing batts and provides better coverage. Loose-fill (batt or rigid foam board) Rafter baffle insulation at consistent depths and to avoid fluffing the in- insulation STEPS FOR INSTALLING LOOSE-FILL AND BATT INSULATION sulation. Rafter baffle Sheathing 1. Seal all attic-to-home air leaks, especially chases, dropped 3. As required by the 1995 MEC, make sure the installer: ceilings, wiring and plumbing penetrations, light fixtures, and bathroom fans. Most insulation does not stop air flow. • Provides attic rulers to show proper blown depth (facing the attic entrance, one ruler for every 300 sq. ft.) Band joist Soffit vent 2. Install blocking (metal flashing) to maintain clearance require- Soffit vent ments (usually 3 inches) for heat-producing equipment found • Provides an accurate attic “report card” showing that in an attic, such as flues, chimneys, and exhaust fans. sufficient density was installed This oversized truss shows loose-fill insulation that is blocked or dammed A raised top plate increases the height for insulation and ventilation at 3. Use only IC-rated recessed lights because they are airtight and ADDITIONAL STEPS FOR INSTALLING BATT INSULATION at the eave with a soffit dam (a piece of fiberglass batt or rigid insulation). the eaves. can be covered with insulation. 1. Cover the top of the ceiling joists or the bottom cord of the truss with insulation. A rafter baffle creates a channel for air flow. 4. Select insulation levels in accordance with the 1995 MEC or the DOE Insulation Fact Sheet.