Attic Insulation R-Value

Installing insulation is one of the best ways to reduce home energy costs. Insulation blocks heat transfer, keeping warm air from escaping from a building during cold winter months, or from entering a building during warm summer months. Hot air rises and flows to cooler air. Blocking airflow prevents exchange of hot and cool air. Insulation traps still air and prevents transfer of heat through air movement, or convection. The effectiveness of insulation is expressed by the R-value, or the resistance to heat flow. The higher the insulation R-value, the more effective the insulation.

One of most effective places to install insulation is the attic of a house. Other important areas include basements, ceilings, floors and walls. Each area may require a different insulation R-value and type of insulation for maximum effectiveness. The most effective R-value for a given structure is calculated according to climate zone, type of heating fuel used, construction materials of the building and whether an air conditioner is used.

There are several types of insulation: blanket batts or rolls, loose fill, foam, rigid fibrous or plastic and reflective. More than one type can be used within the same space. Blanket insulation is usually made of rolls of fiberglass or rock wool in widths that conform to standard attic and floor joist or wall stud spacing. It can be with or without vapor barrier materials. Blanket insulation is easy for do-it-yourself installation.

Loose fill is composed of cellulose, rock wool or fiberglass pellets that are sprayed into the area. This type of insulation is often used for hard-to-reach areas such as walls or places where it may be difficult to lay batts.

Foam insulation is usually installed by a professional with special equipment. Foam may be added to existing insulation or to areas that are hard to reach. It can be an open-cell system, which allows water vapor to pass through the material, or closed cell, which retards water vapor movement.

Rigid fibrous or plastic insulation, made of mineral wool, fiberglass or plastic foams, is used over irregular surfaces such as pipes or heating and air conditioning ducts. It has a higher resistance to heat.

Reflective insulation systems are made from aluminum foils with a backing such as cardboard, plastic film, polyethylene bubbles or kraft paper. This type of insulation is used to reduce downward heat flow in areas such as roof rafters or floor joists. It can be used in combination with other types of insulation and can be easily installed by the homeowner.

Several factors influence the effectiveness of the insulation R-value. Insulation must not be compressed or become wet; this reduces its insulating effectiveness. Blown insulation must be applied in even thicknesses to achieve maximum R-value. Areas around electrical fixtures must be isolated when installing batting to prevent heat build-up which can cause fire. Attic access spaces should also be insulated.

Insulation can be installed during construction, which allows more options for choice of material in walls, floors and basements. Insulation can also be added to existing houses, but installation in hard-to-reach areas may limit the type of material that can be added.

Costs may range between $0.50 to $4.00 per square foot depending on the type of insulation, the insulation R-value and whether installation is done by a professional or the homeowner.