Insulate your attic (but don’t stop there!)
January 13, 2009
Insulate your attic (but don’t stop there!)
Insulating your attic is an excellent way to save on energy usage and to ease the strain on your pocketbook. It sounds simple enough: Add insulation and the savings roll in. However, an insulation project is much more complex than just blowing some insulation into the attic. Modern homes are complex, interactive systems. A large amount of thought and planning should enter into adding insulation.
Done right, insulation reduces heat loss and increases the comfort-level of your home. Once insulation is in place, no ongoing maintenance is necessary. However, done incorrectly, it will not increase energy efficiency; instead, you will waste money and might even cause serious moisture damage to your home. So, how should you go about insulating your residence?
Stop heat flow
To prevent heat from flowing outdoors, we must fix air leaks and systems that cause air to be sucked out of a home. We need to enclose the home in a thermal boundary.
Insulation stops the convective flow of air and, consequently, halts the flow of heat. Fill the attic space above the ceiling with fiberglass or cellulose insulation, the two types of insulation most commonly used in retrofitting a home during remodeling. The insulation halts heat movement into the cold attic, but is a poor barrier when air is moving under even slight pressure – such as through the gaps around a light fixture. In fact, fiberglass is often used as a filter on heating and cooling systems, because air is easily pushed through the thin, fluffy filter on a forced air furnace. In the process, the filter traps dirt from the air.
Seal any gaps that allow air to move from heated spaces into the attic. There are literally hundreds of holes in the thermal barrier, including electrical wiring, light fixtures, plumbing, and the chimney. These openings must be sealed, caulked or foamed, or blocked by metal, wood or drywall.
In modern homes, use a vapor barrier or a vapor retarder on the warm side of the insulation to stop the flow of warm, moist air from your home to the cold exterior. This saves a large amount of heat, prevents the movement of moisture, and limits potential condensation inside walls and the attic.
In drafty older homes, air movement was stopped by plaster, trim and paints. But older homes were quite leaky; a lot of air flowed to the outside, and we lost a lot of heat and moisture. However, air leaks kept the home dry. Years ago we did not care much about wasting energy, because it was dirt cheap. We allowed heat to flow to the outdoors to keep the walls warm and dry.
Approach your home as a system
A goal should be to stop those annoying air leaks. Invest your sealing and insulation dollars where you will gain the most in comfort and payback.
Check the attic first. The insulation level must match your climate. For a cold climate, you need a level of approximately R-38, or about 12 to 15 inches of insulation. R-values measure how effective insulation is. You must close any places for air bypass, where heated air from the house blows up to the attic through any openings or leaks. You may also need to increase the ventilation above the insulation to limit trapped moisture in a space that is no longer heated by heat loss from your home.
Survey the attic for potential air leaks through the thermal boundary from your home. Common culprits include the areas around chimneys, plumbing vents and wire penetrations. The trap door or stairway into the attic can be a major air channel. “Can” lights that penetrate the insulation also create big problems. You may need to hire a professional to help address these leaks.
To find an air bypass into the attic, lift the fiber insulation around the hatch door or near plumbing or electrical wiring. If you see darkened insulation, you have just found an air leak into the attic. The fiber insulation is black because it is filtering out dirt as air passes into the attic. Air leaks and heat loss can occur in another area you may not think of: above dropped soffits, or above the underside of an architectural feature, such as above kitchen cabinets. Often, these areas are not insulated or sealed. Areas above stairways, and around chimneys or major plumbing are also big offenders. For example, a typical Cape Cod home with 1.5 stories is difficult to insulate properly because of the need to work around walls, floors and ceilings, that have a high potential for air movement.
Also, you must route all kitchen and bath exhaust fans to the outside, instead of into the attic. In the 1950s and 1960s it was common to direct exhaust fans into the attic. This measure was likely successful because the insulation was also poor and, in effect, we heated the attic with heat from our homes. Because the attic was warm, condensation and moisture did not create a problem.
In many climates, the attic should have a minimum R-38 insulation level, but check with government resources and local contractors to determine the correct level in your area. Remember to insulate and to seal any trap doors and stairways into the attic; they are the big losers.
Insulate on top of old insulation
You can add insulation on top of existing insulation, but avoid creating any air gaps. The insulation should fit tightly ontothe lower layer of existing insulation. If the space between ceiling joists, or horizontal pieces that support the floor or ceiling, is filled with insulation, you can add batts parallel or perpendicular to the framing.
If existing insulation is below the framing, you should fill in the voids, and blowing insulation over the top may be the best bet.
Attic - Maintain or add ventilation
Part of adding insulation to the attic is maintaining, or improving, adequate attic ventilation above the insulation. The ventilation should be divided between the overhangs and the ridge of the roof. When insulation is added, it is very important to keep the areas above soffit vents clear for air movement. This is because if you block these areas with insulation, you can create moisture problems. In older homes, these areas should be checked, because often they are blocked with insulation.
Government resources
You can find more information and resources at the U.S. Department of Energy’s Energy Star Web site, www.energystar.gov. This excellent Web site includes step-by-step information about choosing and installing insulation. It details R-value recommendations for various surfaces and climates.
Another good resource is the Department of Energy’s Energy Efficiency and Renewable Energy site at http://www.eere.energy.gov/consumer. It provides information on home energy audits, contacts, and a multitude of related topics.
Use a pro?
Yes, it is a good idea to have a professional evaluate the condition of your home and perform much of this work. If you are considering blowing in insulation or addressing “can” lights that penetrate the thermal barrier, you would benefit enormously from hiring a professional. Although this article will help you begin thinking about insulation, a professional will be a big help with details and climate-specific information.
Confused?
Sure – so are many insulation contractors. You need to do a little research and locate a contractor who wants to discuss air leakage, bypass, and the thermal envelope. If a contractor does not mention these items, look for a better contractor.
Our homes are complicated systems. Spraying a little insulation into the attic may not solve your heat loss and energy cost problems. It may even cause more problems. However, with proper thought, planning and sealants, you are much closer to getting the job done right.