Department of Energy
Energy Efficiency and Renewable Energy
Insulating a New House
Insulating a New House (Do It Right the First Time)
If you are buying or building a new house, make sure that energy-saving features are included. The Federal Trade Commission (FTC) home insulation rule requires the seller of a new home to provide information on the type, thickness, and R-value of the insulation that will be installed in each part of the house in every sales contract. Many state or local building codes include minimum requirements for home insulation. Be sure that your new home or home addition meets these building codes. You may wish to install insulation beyond the minimum specified in such codes, especially if those minimum levels are below those recommended here. Also, Energy-Efficient Mortgages are available through both government-insured and conventional loan programs. These mortgages recognize that the homeowner's energy payments will be less for a more energy-efficient home, and therefore enable a buyer to borrow a larger sum to cover the up-front costs of improving the house's energy efficiency.
To keep initial selling prices competitive, many home builders offer standard (not optimal) levels of insulation, although additional insulation would be a good investment for the buyer. Builders participating in the Energy Star Program use third-party inspectors to not only ensure that the correct amount of insulation has been used, but also to ensure that it has been installed correctly.
Now is also the time to make your home air tight. Special products and techniques are available to eliminate air leaks between the walls and floor and between the
walls and ceiling. Encourage your
builder to make all clearances around doors and windows as tight as possible and to properly
caulk and seal all such joints.
Where and How Much?
Where and How Much?
Figure 1 shows which building spaces should be insulated. Discuss the house plans with your builder, and make sure each of these spaces is properly insulated to the R-values recommended here. Remember to buy the insulation based on this R-value, and to check the product label to determine the insulation's proper thickness, especially if you plan to install it in a confined space, such as in wall cavities and cathedral ceilings.
Figure 2 shows the Department of Energy's climate zones, along with a short summary of our insulation recommendations for new houses. These recommendations are based on comparing your future energy savings to the current cost of installing insulation. A range is shown for many locations for these reasons:
So, how should you decide how much insulation to install?
The future energy savings, of course, depends upon how much energy costs in the future. Our best estimate is that fuel costs will rise at approximately the same rate as general inflation. If you think that fuel costs will increase more than that, you should install the greater amount of insulation shown. Looking at the map, if you think the energy costs in your area are greater than energy costs for other locations in same climate zone, you should install the greater amount of insulation.
We can also give you better guidance for your specific location and recommendations for other insulation locations in your home. The ZIP-Code calculator will actually let you enter your own insulation prices, energy costs, and heating and cooling system efficiencies. However, some personal computer security systems won't allow Java programs to run properly. The recommended R-values table can be helpful in those cases, because it will provide recommendations based on insulation and energy costs for your local area.
Foundation insulation options for new construction are broader than for existing homes. The builder may, for example, choose to insulate the exterior of a basement or crawlspace wall. You should discuss termite inspection and control options with your builder when choosing your foundation insulation method. Special sill plate (the joint between the top of the foundation and the bottom of the house frame) mineral fiber sealing products are designed to reduce air leaks if installed during the initial house construction. All flammable insulations or insulation facings must be covered or otherwise protected to meet fire codes. More information is given in the Basement Insulation Technology Fact Sheet.
If water lines and the ducts of your heating or air-conditioning system run through unheated or uncooled spaces, such as attic or crawlspaces, then the water lines and the ducts should be insulated. Make sure your contractor checks the ductwork for air leaks before installing the duct insulation. The contractor should then wrap the ducts with duct wrap insulation of R-6 with a vapor retarder facing on the outer side. All joints where sections of insulation meet should have overlapped facings and be tightly sealed with fiber glass tape; but avoid compressing the insulation, thus reducing its thickness and R-value.
Return air ducts are more likely to be located inside the heated portion of the house where
they don't need to be insulated, but they should still be sealed off from air passageways that
connect to unheated areas. Drywall- to-ductwork connections should be inspected because they
are often poor (or nonexistent) and lead to unwanted air flows through wall cavities.
Air sealing is important, not only because drafts are uncomfortable, but also because air leaks carry both moisture and energy, usually in the direction you don't want. For example, air leaks can carry hot humid outdoor air into your house in the summer, or can carry warm moist air from a bathroom into the attic in the winter.
Most homeowners are aware that air leaks into and out of their houses through small openings around doors and window frames and through fireplaces and chimneys. Air also enters the living space from other unheated parts of the house, such as attics, basements, or crawlspaces. The air travels through:
There are several fact sheets that will help you stop these air leaks:
When natural ventilation has been sharply reduced, as
in a more energy-efficient house, it may be necessary to provide fresh air ventilation to avoid
build-up of stale air and indoor air pollutants. Special air-to-air heat exchangers, or
heat-recovery ventilators, are available for this purpose. It is also possible to incorporate a supply of fresh
outside air into your heating and cooling system. This arrangement can be used to create a slightly higher
pressure inside your home, which will prevent uncontrolled outside air infiltration into your home.
For more details on this arrangement, see "Integration with forced-air heating and air-conditioning systems"
Whole-House Ventilation Systems Technology Fact Sheet.
Moisture Control and Ventilation
Moisture Control and Ventilation
We talk about moisture control in an insulation fact sheet because wet insulation doesn't work well. Also, insulation is an important part of your building envelope system, and all parts of that system must work together to keep moisture from causing damage to the structure or being health hazards to the occupants. For example, mold and mildew grow in moist areas, causing allergic reactions and damaging buildings.
Moisture can enter your home during the construction process. The building materials can get wet during construction due to rain, dew, or by lying on the damp ground. Concrete walls and foundations release water steadily as they continue to cure during the first year after a home is built. During the house's first winter, this construction moisture may be released into the building at a rate of more than two gallons per day, and during the second winter at a slower rate of about one gallon per day. You may need to use dehumidifiers during this initial time period.
When Is Moisture a Problem?
Four Things You Can Do to Avoid Moisture Problems:
Should you use vapor retarders?
Moisture can travel from the ground
foundation and up into your walls, and through slab floors into your home. So your builder
should always include a vapor retarder between the foundation and the walls.
Should you include a vapor retarder in your wall? If so, where? If the outside air is
colder and drier than the inside of a home, then moisture from inside the warm house will
try to diffuse through the walls and ceiling toward the cold, dry outside air. If the
outside air is hot and humid, then moisture from outside will try to diffuse through the
walls toward the dry, air-conditioned inside air. We used to tell people to install vapor
retarders to try and stop this moisture diffusion. But we have learned that if moisture
moves both ways for significant parts of the year, you're better off not using a vapor
retarder in the walls at all.
Your builder will most likely hire a subcontractor to install the insulation in your new home. However, it is a good idea to educate yourself about proper installation methods because an improper installation can reduce your energy savings.
Radiant barriers may be installed in attics in several configurations. The radiant barrier is most often attached near the roof, to the bottom surface of the attic truss chords or to the rafter framing. A radiant barrier should never be placed on top of your insulation or on the attic floor because it will soon be covered with dust and will not work. A separate DOE fact sheet is available for radiant barriers to show which parts of the country are most likely to benefit from this type of system.
Blown-in cellulose or spray foam can be used to fill wall cavities. Both of these products can do a good job of filling in the space around wires and other obstructions and in filling any oddly-shaped areas. For cellulose, some form of netting is used to hold the cellulose in place until the drywall is installed. For spray-foam, it is important that the application be finished off neatly to avoid problems with the drywall installation.
Masonry walls should be insulated on the exterior
Design Option: Crawlspaces and Slabs
Many building codes presently require installation of crawlspace vents to provide ventilation with outside air, but there is no compelling technical basis for crawlspace ventilation requirements. If the crawlspace is vented, the floor should be insulated and any pipes or ducts in the crawlspace should be insulated as well. In some climates, pipes in vented crawlspaces must also be wrapped with heat trace wires to avoid frozen pipes. If the crawlspace is not vented, it is crucial that all of the crawlspace ground area be covered with a durable vapor retarder, such as heavy-weight polyethylene film. (This is also a good practice for vented crawlspaces.) For unvented crawlspaces, the insulation should be placed on the inside wall of the crawlspace instead of under the floor above. The insulation should also extend a few feet over the ground surface inside the crawlspace, lying on top of the durable vapor retarder. For the unvented arrangement, the air within the crawlspace is actually incorporated as a part of the conditioned space within the house, as if it were a basement. The Crawlspace Insulation Technology Fact Sheet gives more details about this design option. If you choose a slab foundation, be sure to follow the recommendations for insulation installation and moisture control found in the Slab Insulation Technology Fact Sheet.
Design Option: Advanced Wall Framing
Advanced wall framing techniques can be used that will reduce the energy losses through the walls with little or no additional costs. Details are given in the Wall Insulation Technology Fact Sheet.
Design Option: Metal Framing
Some new homes are built using metal frames instead of wood. Such frames are not susceptible to insect problems that can damage wood-framed structures. However, when you insulate a metal-framed building, it is important to recognize that much more heat flows through metal studs and joists than through pieces of wood. Because of this difference, placing insulation just between the wall studs, or just between attic or floor joists, doesn't work as well for metal-framed houses as it does for wood-framed houses. If your walls have metal frames, you will need to place continuous insulative sheathing over the outside of the wall frame, between the metal framing pieces and your exterior siding in addition to insulating the space between the studs. (Note that this insulative sheathing cannot take the place of plywood or other seismic bracing.) If your attic has metal joists, you may want to place rigid foam insulation between the joists and the ceiling drywall and to cover the attic joists with insulation to the extent possible.
Design Option: Insulating Concrete Forms
Insulating concrete forms can be used to construct walls for new homes. These special concrete walls come in a variety of configurations and can provide additional thermal mass to your home to help reduce the effect of outdoor temperature swings.
Design Option: Massive Walls
The most common house type in this country is the light-construction frame house. Massive walls are less common, and include buildings made from concrete, concrete block, and log. These buildings will use less energy than wood-frame construction in many parts of the country because they can store heat from the daytime sun to provide needed heat at night, or can cool down at night to reduce air-conditioning loads during the day. Research shows that such massive wall systems perform best if the insulation is located on the outside of the wall. See the ZipCode Calculator or the ZipCode table to find out how much insulation you should use.
Design Option: Structural Insulated Panels
Structural insulated panels can be used to construct a house. These panels sandwich plastic foam insulation between two layers of a wood or composite product, thus eliminating the need for structural wood framing members. These systems save energy in two ways, first by reducing the heat losses that would have gone through the wood frame, and second by reducing air leaks. Both of these changes represent significant energy savings. Just stopping the energy flowing through the wall framing could save 25% of the wall's energy losses.
Design Option: External Insulation Finish System
Some homes are built with an External Insulation Finish System that gives a stucco-like appearance. In the past, there were quality control problems where poor construction led to water leaks into the wall system, usually around window frames. Newer versions of the external insulation finish system have been designed to be more robust and to allow any water entering through a construction defect to drain harmlessly out of the wall. This system can be used to finish wood-framed, metal-framed, and masonry walls. It offers special advantages for the metal-framed and masonry walls because the continuous external insulation layer optimizes the thermal performance of both of those two wall systems.
Design Option: Attic Ventilation or a Cathedralized Attic
It is important that the house design, and construction, minimize the transfer of moisture from the living space to the attic. To handle any moisture that does migrate into the attic, traditional attic design calls for ventilation. Attics may be ventilated with a combination of soffit vents at eaves and continuous ridge vents. Attic vents may also be installed in gable faces. Many codes and standards require one square foot of unobstructed ventilation opening for each 300 square feet of attic floor area if a vapor retarder is included in the ceiling separating the attic from the living space. Twice as much ventilation is recommended if there is no vapor retarder. The net free area of a vent is smaller than its overall dimension because part of the vent opening is blocked by meshes or louvers. The openings should be equally distributed between the soffit and ridge vents or between each gable face. Never cover or block vents with insulation. Use baffles to prevent loose-fill insulation from clogging vents.
During the house design phase, you can choose a cathedralized attic, which is not ventilated, unless attic ventilation is required by code in your area.
Next Section - Adding Insulation to an Existing House
André O. Desjarlais