Why

Insulation slows down the flow of heat-in the winter it helps keep heat in the house and in the summer it helps keep heat out. A well-insulated house saves energy, lowers your heating and cooling bills and allows you to get by with smaller-capacity heating and air conditioning systems. The more you insulate, the more your energy savings can add up. By keeping temperatures more moderate, and reducing drafts, insulation can also create a more comfortable home year-round.

The basic rule of insulation is that any surface in your home that's directly exposed to the outside climate or an unheated adjacent space-roof, exterior walls, ceiling, floor-is a candidate for insulation.

Recommendation

Insulation is installed during construction and is rarely upgraded (particularly in concealed areas such as walls) over the life of the building. You can achieve higher levels of insulation with only a slight increase in material cost; the labor cost remains the same. Why not maximize the opportunity when you have the chance? The greatest gains from increased levels of insulation will be in climates that get really hot or cold and where air conditioning or heating is needed to keep the home comfortable.

In new construction, increase ceiling, exterior wall and floor insulation to exceed Title 24 minimums as follows:

	Recommended	Minimum*
Ceiling	R-30 to R-38 (11")	R-19
Wall	R-15 (high density batt) or higher	R-13
Floor**	R-19	R-13

*These numbers represent the absolute minimum requirements for wood-frame construction statewide. Higher insulation levels are normally required where simplified compliance methods are used.

** Over garages/crawl spaces.

Most older homes are underinsulated and would benefit from upgrading. Additional ceiling insulation offers the greatest energy savings for the least cost. Add extra insulation to exterior walls and floors when possible as part of renovation projects. If you decide to upgrade your insulation, be sure to do the job right or you will not receive the full benefit of the extra insulation. Poorly installed insulation is only half as effective.

To determine whether you should add insulation, you first need to find out how much insulation you already have and where. A "rule of thumb" is that every inch of fiberglass batt or blown-in loose-fill insulation has an R-value of about 3.5, so six inches of blown-in insulation will have a total value of R-21.
Go to the U.S. Department of Energy's website to learn more about checking existing insulation www.ornl.gov/sci/roofs+walls/insulation/ins_04.html.

Ceiling

Attics. Because they are easily accessible, attics are among the easiest places to add insulation in an existing house. And since heat rises, this can also be the most effective location to add extra insulation.

Attics can be challenging to insulate properly, however, because of all the equipment, obstacles and difficult-to-reach spaces. Insulation must be snug around HVAC systems, light fixtures, ducts, plumbing and electrical wires, and this takes special attention to detail.

Although batt insulation is common in attics, loose-fill (cellulose or fiberglass) or spray-applied foam insulation are better at surrounding attic obstacles and filling air gaps.

Warning: Vermiculite insulation, which looks like brownish-pink/silver accordion-shaped chips and was common in attics of homes built before 1950, can contain asbestos. Don't disturb it. Only insulation contractors certified to handle and remove asbestos should deal with vermiculite insulation.

Cathedral Ceiling & Roofs. When it's time to reroof, consider adding a layer of rigid foam insulation and decking on top of the existing roof and then shingling over that. Rigid board insulation has an R-value of up to 6.5 per inch of thickness, depending on the insulation material.

Adding extra insulation to a cathedral ceiling can be difficult. Consult with a licensed insulation contractor to find out if this is feasible in your situation.

If roof framing provides insufficient space for desired insulation, higher insulation values can be obtained by either attaching furring strips to the underside of the rafters (creating room for additional insulation to be installed), using high-density batts (high-density R-30 batts are about the same thickness as R-25 batts and fit into 2-by-10 framing) or adding rigid foam insulation under the rafters.

Walls

Exterior walls account for up to half of the surface area of a house, so it is important that they are insulated well.

New Construction. During construction, walls may be insulated with nearly any type of insulation. Because of the limited space, higher R-value types of insulation are a good choice in walls. Increasing insulation beyond minimums with fiberglass batts can present challenges if the house has 2-by-4-stud wall cavities. R-13 fiberglass batts are 3-1/2" thick and just the right size to fit between the studs. R-19 is 6-1/4" thick and requires 2-by-6 wall construction. However, there is a high density R-15 insulation that fits the standard 2-by-4 stud spacing.

Rigid foam insulation added to the exterior will also increase the total wall R-value, regardless of the framing spacing. Half-inch thick rigid foam-insulated sheathing provides an R-value of R-2 to R-3.5; thicker sheathing will yield even higher R-values. With steel framing, where thermal bridging is significant, the use of rigid foam insulation offers even greater benefits.

Thermal Bridging

A thermal bridge is created when materials that are poor insulators come in contact. Wood studs are poor insulators; steel studs are even worse. Typically 25% of the wall area of a home is framing, and unless insulated, heat will flow freely through the joists and studs. Installing insulation over the studs, such as with rigid foam sheathing, does a good job of reducing thermal bridging.

If building a stick-frame house, consider using advanced wall-framing techniques These techniques, such as using 2-by-6 stud spaced on 24-inch centers, improve the whole-wall R-value by reducing thermal bridging and maximizing the wall area that is insulated. Click for more information on advanced wall-framing techniques: www.eere.energy.gov/buildings/info/documents/pdfs
/26449.pdf.

Existing Walls. Upgrading wall insulation in existing houses can be difficult and expensive. It usually involves drilling holes through exterior walls and pumping in insulation. Walls with existing loose-fill insulation can be blown full of new cellulose or fiberglass to increase the density, thereby increasing the R-value. Blown-in insulation can tend to settle over time, however, creating gaps at the top and compromising the effectiveness of the insulation.

When the interior walls or exterior siding on a house is being replaced, wall insulation can easily be installed or upgraded. Also, don't miss the opportunity to add insulation when walls are accessible during door or window replacement. If the outside siding is being replaced, it is often cost effective to apply rigid foam insulation on the outside of the framing before the siding is installed.

Floors

Uninsulated floors can be a significant source of heat loss from the living space, particularly if the space underneath the floor is not conditioned (heated), like a garage or crawl space. Insulating the floors above your unheated garage will help reduce the energy costs for the rooms above.

For ground floors use unfaced fiberglass batt insulation installed to the capacity of the floor joist depth and supported from below with netting, wire or metal rods if necessary. Rigid foam insulation can also be installed to the underside of floors to improve thermal performance.

Types

Insulation materials work because they have millions of tiny air cells that slow heat's movement, and there are many types of materials that do this. All types of insulation have their advantages and disadvantages. Considerations when choosing a type include the nature of the material the insulation is made from-some are more environmentally friendly than others and some present health concerns; the effectiveness of the material at filling the space and sealing air spaces; whether it can be easily installed by the homeowner or requires a professional installer; and the performance of the material over time.

Fiberglass: R-2.9 to R-3.8 per inch; high-density batts: R-3.6 to R-5 per inch; loose-fill: R-2.2 to R-2.9 per inch

Fiberglass insulation is manufactured by melting sand and recycled glass into glass fibers which are held together with a binder. Typical recycled content ranges from 20% to 30%. Fiberglass is noncombustible, does not wick-up water and returns to its original R-value after drying. Fiberglass insulation with no added formaldehyde is widely available, and can be used anywhere that fiberglass batt is used.

Fiberglass generally comes in batts and blankets; batts are precut and blankets are in a continuous roll. Fiberglass batts are available in widths suited to standard spacings of wall studs and attic or floor joists. Continuous rolls can be hand-cut and trimmed to fit. They are available with or without vapor retardant and reflective facings. Unfaced batts in general do a poor job of preventing air infiltration.

Loose-fill fiberglass can be blown into attic spaces to almost any R-value. Batts can be installed by the do-it-yourselfer, while loose-fill must be professionally installed. This insulation is most commonly installed in walls and attics, as well as raised floors and floors over garages, crawl spaces and basements.

Common Batt R-Values and Uses:

• R-13 is 3-1/2" thick and is appropriate for 2-by-4-stud wall cavities.
• R-19 is 6-1/4" thick and is used in 2-by-6 wall construction and in attics.
• R-30 (9-1/2" thick) and R-38 (12" thick) are made specifically for attic insulation.

Cautions: While fiberglass batts are made in widths suitable for standard stud spacing, many areas within a building's framing do not conform to this standard spacing. To make the insulation fit exactly in this odd-spaced framing, as well as around pipes, light fixtures, plumbing and other obstacles, requires very careful installation. Improperly fitted batt type fiberglass insulation often does a poor job of preventing infiltration because gaps or openings remain after installation. Air infiltration can be reduced by adding a layer of cellulose loose-fill on top of the material.

Fiberglass insulation is still required to carry a cancer warning label in the USA. It is considered a risk because of the insulation fiber's ability to become airborne and be inhaled, similar to asbestos. There are also concerns about the glues used to hold together the fiberglass. Newer forms of fiberglass insulation are considered less harmful than traditional fiberglass because they are less prone to become airborne, use less glue and are less likely to irritate skin.

Fiberglass can be an irritant so wear gloves, a respirator and other protective gear.

Loose-Fill Cellulose: R-3.5 to R-3.8 per inch

Cellulose insulation is made from post-consumer recycled newspaper, is treated with fire retardants and does not have added formaldehyde. Loose-fill cellulose insulates as well as high-density fiberglass batts and also adds acoustical insulation.

Cellulose's small particle size and granular composition make it easy to blow into difficult-to-reach spaces and surround and seal cavities and voids, so cellulose performs better thermally and acoustically than fiberglass batts. Loose-fill cellulose can be blown into attics, finished wall cavities, and hard-to-reach areas. It can also be combined with water-based adhesives and sprayed in place. Loose-fill cellulose can also be used to bury (and insulate) ductwork.

Some building supply stores provide cellulose blowers for do-it-yourself applications.

One drawback of insulating with cellulose is that the material can settle over time. The Insulation Contractors Association of America recommends that an additional 25% of thickness be added above the labeled settled thickness.

Spray Foam: R-3.5 to R-6.2 per inch

Spray foam is a plastic liquid that expands when sprayed into walls, ceilings and floor cavities. It expands into all nooks and crannies and attaches to any surface, providing exceptional thermal insulation-about twice the R-value per inch of traditional batt insulation.

Spray foam comes in both open-cell and closed-cell forms. Closed-cell has higher R-value per inch (6.2 vs. 3.5), higher strength, and is more resistant to air and water leakage; it is also more expensive than open cell.

Spray foam also forms a complete air and moisture barrier, acts as a good sound barrier, increases structural stability, does not support bacterial growth or provide food for pests, and is fireproof.

Spray foam insulation must be professionally installed using special equipment to meter, mix and spray the material into place. Formulas can be modified to vary the foam's physical properties depending on the use desired.

Spray foam insulation materials are manufactured with non-CFC blowing agents, though some do use HCFCs. Once installed the material is inert and will not release harmful chemicals into the air. There's also a new spray foam product on the market made from soybeans, a renewable resource.

Spray foam insulation and installation usually cost more than traditional batt insulation, but can reduce other costs and tasks associated with weatherizing a home, such as caulking, applying housewrap and vapor barrier, and taping joints, because spray foam insulation also forms an air barrier. When building a new home, this type of insulation can also help reduce construction time and the number of specialized contractors, which saves money.

Spray foam insulation works for walls, ceilings and crawl spaces. A slow-curing variety, which flows over obstructions before it expands, can be used for empty wall cavities in existing buildings.

Cautions: Foam insulation must be protected from sunlight as ultraviolet rays may damage it.

All spray foam insulations, except cementitious foam and Icynene, are flammable, release toxic fumes when they burn and require protection with fire-rated drywall on the interior of a house. Do not use near flammable applications, such as flue vents.

Rigid Foam Insulation: R-3.9 to R-6.5 per inch

Rigid foam insulation, or rigid foam sheathing, is applied directly to framing as rigid sheets. Rigid foam insulation can be used to insulate almost any part of your home. It provides good thermal and acoustical insulation and can add structural strength to the building without adding much weight. When the joints between panels are properly sealed, rigid foam insulation offers coverage with few heat loss paths and can act as both an air and vapor barrier, even as it prevents thermal bridging through steel and wood studs. Rigid foam typically has a higher R-value per inch than fiberglass, and it's easy to work with. As with spray foam, rigid foam insulation comes in both open-cell and closed-cell forms. Closed-cell has higher R-value per inch, higher strength and is more resistant to air and water leakage; it is also more expensive than open-cell.

Rigid foam insulation is helpful where space is limited but a high R-value is needed, such as in cathedral ceilings. It can be installed on the interior or exterior of a wall, but on the inside it must be covered by a fire-resistant material like wallboard. This type of insulation can also be added to basement walls, exposed foundations, under or on top of the roof sheathing, crawlspaces, attic accesses and over a slab-on-grade floor.

Cautions: Several different types of plastic are used to make rigid foam insulation. As with spray foam insulation, rigid foam insulation must be protected from sunlight to prevent degradation and, though hard to ignite, it is flammable and releases toxic fumes when it burns.

In the past, ozone-depleting CFCs and other harmful chemicals were used in manufacturing rigid foam insulation; today most are made with HCFCs, which are far less destructive to the ozone layer than CFCs, but damaging nonetheless. A few products are available that use blowing agents that are not ozone-damaging.

Rigid foam insulation tends to be more expensive than other types of insulation.

Cotton: R-3.4 per inch

Cotton batts are made from recycled textile scraps. Installation would be the same as for any batt material. However, sharp knives must be used as the material can be difficult to cut. The material is less of an irritant than fiberglass. Cotton batts are considerably more expensive than fiberglass.

Mineral Wool: R-3.1 per inch

Mineral wool insulation includes both slag wool and rock wool. Slag wool is more common and is a recycled industrial waste product. Rock wool comes from natural rocks, such as basalt or diabase. It is available as blow-on wall insulation, as loose blow-in attic insulation, and as batts. Blow-on application will seal wall cavities, offering superior insulating service compared to batts. Mineral wool will not burn, and is chemically inert.

Caution: Mineral wool fibers are similar to fiberglass in their ability to become airborne and be inhaled.

Other Ways to Improve Insulation

Install a Radiant Barrier: Consider adding a radiant barrier in your attic in addition to insulation. Click here for more information on radiant barriers.

Seal Air Leaks: Insulation works much better when air is not moving through or around it. So it is very important to seal air leaks before installing insulation to ensure that you get the best performance from the insulation. See the Resources section below for links to helpful websites.

Use SIPs: Structural insulated panels (SIPs) are pre-fabricated exterior wall and roof panels made up of a thick slab of expanded polystyrene insulation sandwiched between two layers of plywood or oriented strand board. SIPs are growing in popularity as an alternative, highly-insulative, wall material. The SIPs provide the structural support, rather than the studs used in traditional framing. SIPs come in various thicknesses.

Use ICFs: Insulated concrete forms (ICFs) are rigid plastic foam forms that hold concrete in place during curing and remain in place afterward to serve as thermal insulation for concrete walls. The foam sections are lightweight and result in energy-efficient, durable construction. ICF walls provide higher R-values and lower air infiltration rates than typical wood-frame construction.