An attic with too little insulation is wasting your energy dollars in both winter and summer. Insulation is designed to resist heat flow in either direction and should be installed between conditioned and unconditioned areas of a home to help cut both your heating and air conditioning costs. The most common forms of insulation include fiberglass batts and cellulose or fiberglass loose fill.
Loose fill fiberglass and cellulose or fiberglass batt insulation are relatively inexpensive, and installation usually pays for itself in two to eight years, depending on the situation. Fiberglass batts can be easily installed by the average homeowner. Cellulose or loose fiberglass is typically installed using an insulation blowing machine. For small areas or "topping off" existing insulation, either material can be poured and spread out by hand. For larger areas, consider using an insulation contractor or check into the possibility of renting an insulation blower.
Insulation levels are referred to by R-value. The R-value of a given insulation material is an indication of how well it resists the transfer of heat. The higher the R-value, the better the insulation will reduce heat loss or gain.
The first step in determining the need for more insulation is to measure the thickness of the existing insulation and estimate the R-value (see chart below). Keep in mind that adding more insulation has diminishing returns. For example, the first R-11 of ceiling insulation pays for itself very quickly, whereas the next R-11 added will have a longer payback.
| Insulation Type | R-Value/Inch* |
| Fiberglass batts/blankets | 3.2-3.5 |
| Loose-fill fiberglass | 2.2-2.5 |
| Cellulose | 3.7 |
Attic Insulation
The amount of insulation you can install in your attic is determined by the size of the joists and whether or not your attic has a floor. A minimum of R-30 is recommended in most climates, but is not always possible. You will also want to determine whether to install fiberglass or cellulose.
You or the contractor you hire should complete a number of preliminary steps before insulating your attic, as follows:
- Identify all recessed lighting fixtures, vents, chimneys, and other
heat producing devices in all areas where insulation is to be installed.
Block off recessed light fixtures with a sheet metal barrier or one
of the various products commercially available. Blocking must be at least
as high as the height of the finished insulation and should be installed so that
ensures that all devices which may require maintenance or service remain
accessible after the insulation is installed. A three inch minimum clearance
between the fixture and the insulation must be maintained. In addition,
do not cover recessed light fixtures unless they are specifically labeled as "IC"
("insulation coverage") rated. A clearance of three inches must
also be maintained between chimneys, flues, vents, or other heat sources.
- Inspect the room, ceiling, or attic floor to identify previous or
current moisture problems. Signs include paint peeling, warping, stains,
fungus growth, rotting, or other structural damage. Do not install insulation
in these areas until any moisture problems have been corrected.
- Inspect the ceilings to ensure they will carry the weight of the insulation.
(In most cases this is not a concern, as both fiberglass and cellulose
weigh very little.)
- Install permanent blocking to prevent loose-fill insulation from clogging
soffit vents at the eaves. (This would restrict attic ventilation.)
- Cover wall and drop ceiling cavities to prevent filling these areas
with insulation.
- If knob and tube wiring is present, a licensed electrician should
certify that insulation can be safely installed.
- Once the above steps have been completed, insulate all attic areas
to recommended level, usually R-30. A floored
attic may limit the amount of insulation that can be installed. To maximize
your energy savings, you should also insulate all attic entryways such as hatchway openings,
kneewall access doors, and walk-up stairways.
Attic Ventilation
Here is a basic rule to keep in mind: Never install insulation in an attic space unless adequate and permanent ventilation exists or can properly be installed. Attic ventilation reduces summer heat build-up and prevents winter moisture condensation. Both problems can be costly and damaging, and both can be virtually eliminated by effective attic ventilation.
Differences in home construction and design are a major factor in choosing the right type or combination of vents. Vent location, style, and size are all factors to consider when insulating your attic.
A qualified contractor will know the formula by which to determine how much ventilation you will require. Important factors in the formula include the existence of vapor retarders, location of existing ventilation in relation to the eaves, and square footage of the attic.
The contractor should be able to tell you the type, number, and location of all vents to be installed. Choices will include roof vents, gable end louvers, rectangular louvers, soffit vents, ridge vents, and turbine vents. It goes without saying that all necessary precautions should be taken to ensure a watertight installation.
