Various types of products are used for ceiling insulation. Batt insulation is made of spun fiberglass, usually attached to some sort of backing- paper, plastic or foil. Insulation which is designed to be poured in loose form between the rafters is usually made of fiberglass, cellulose, rock wool, polystyrene, vermiculite or perlite. In certain applications, such as cathedral ceilings, sheet styrofoam is used.
The type and amount of insulation needed will be regulated by local codes. However, it is easy to determine the recommended R-value for where you live. In the United States, zones have been determined, based on Heating Degree Days (HDD). These total the number of degrees which a building must be raised above the ambient temperature, times the number of days this will be needed. These zones range from 1 to 5, and the R-value of insulation required increases from 19 to 49, accordingly. The greater the R-value, the better insulation is provided.
Loose insulation is ideal for ceilings with attics above them because it will conform easily to spaces between joists, which may be divided by a number of cross members. The most difficult part of the application is to properly preserve space around heat-producing items such as recessed lights or heating ducts. These need to be protected by baffles of metal, plastic, cardboard, or batt insulation.
In an attic, it is important to add enough ceiling insulation to prevent heat loss from the living space. Ventilation is also necessary to reduce condensation which can damage stored items and construction materials, and compress the insulation. Most codes still require ridge vents at the roof peak, and soffit vents. Air entering through the soffit vents need to be directed upward along the trusses by the use of baffles so that it does not flow through the insulation.
Attics with knee walls need additional work. Air will often flow underneath, breaking up the desired air-flow pattern from soffit to ridge. Ideally, ductwork will be installed to the outside of the knee wall, and the space properly sealed, separating it from the attic space.
If batt ceiling insulation is used, it should be installed with the vapor barrier down, next to the living space. Be sure to use a thick enough batt to meet the R-value requirement. Never compress a fiberglass batt, as this reduces its R-value. If there are wires to be worked around, cut a channel in the batt for the wire. Be sure to adequately seal around all access ports.
Cathedral or vaulted ceilings must be treated differently. Usually 2×12 rafters are used to provide adequate space for batt insulation. Baffles for ventilation channels are required. Rigid foam sheets and a fire-protection layer are added under the rafters for extra protection before the interior ceiling is installed.
Some insulation materials are treated to be fire-retardant. Properly installed insulation reduces moisture retention in a home, helping to prevent the growth of mold.
Whichever type of ceiling insulation is the best for your home, proper application is certain to improve the quality of your living space. A well-insulated home is not only more comfortable, but safer for your family.