Flexible insulation is manufactures in two forms - batts and blankets – both made of fibrous materials such as glass fibers, wood fibers, rock wool or cotton. Organic fibers are chemically treated to make them resistant to fire and decay. Batts are pre-cut in four- or eight-foot lengths, and are available in thicknesses between two and six inches. Blankets are furnished in continuous rolls and are available in thicknesses between 11/2 and 3 inches. In order to be readily used in homes that have been constructed with joist and stud spacing of 16 and 24 inches, both batts and blankets are manufactured in 15- and 23-inch widths.
Loose-fill insulation is usually made from rock wool, glass fibers, pearlite, vermiculite, cellulose, granulated cork, shredded redwood bark, sawdust or wood shavings. Loose-fill insulation is suited for use in the sidewalls of homes that were not insulated during construction, or between the floor joists of unheated attics. If there is no floor covering, loose-fill insulation is not recommended for use between the floor joists.
Rigid insulation is typically made from extruded polystyrene, polystyrene bead board, fiberglass, urethane, or wood fiberboard, and it is often used to insulate masonry walls. It comes in 24- and 48-inch widths. However, most rigid insulation boards are not fire resistant and should be covered with at least ½-inch gypsum wallboard in order to ensure fire safety. Rigid insulation boards are used as backer boards for aluminum and vinyl siding as well.
Foamed-in-place insulation was among the most popular types of insulation in the late 1970s, and it was made from urea formaldehyde. In many houses, however, the foam ingredients were improperly mixed and installed, resulting in excessive formaldehyde vapor being released into the house and causing adverse side effects. This type of insulation is not longer being installed, but many homes still have it in their walls. On the other hand, it is no longer considered a problem.
The effectiveness of insulation can be measured according to its resistance to heat flow – the R number. The higher the R-number, the greater the resistance to winter heat loss or summer heat gain.
R-numbers are additive, meaning that you can add a home insulation rated R-11 to one that is rated R-19 to achieve a resistance value of R-30. The thermal resistance of an area covered with loose-fill or flexible insulation can change over the years, and the insulation value depends not just on the material, but also on the amount of trapped air contained within the material.
For an energy efficient home and lower energy bills, home and building owners should insulate all exterior walls with the proper type of insulation and the adequate R-value. The R-numbers, however, are based on current and projected fuel costs, so if your house is already insulated you can add the difference once you determine the amount of existing insulation.
To determine whether your house is properly insulated, check the exterior walls, as well as the ceilings and floors that face unheated areas, such as the attic and crawl space. In unfinished areas where the insulation is exposed, the thickness can easily be measured. Determining the amount of insulation in a finished exterior wall is more difficult, but you can feel the inside surface during the heating season to make a quick determination whether the wall has no insulation or is inadequately insulated. If the wall is cold to the touch, more insulation is necessary.
While determining the amount of insulation, you should also check whether there is a vapor barrier associated with the insulation. A vapor barrier is a thin sheet material such as aluminum foil, polyethylene film or an asphalt-impregnated kraft paper, through which water vapor cannot readily pass. Many types of insulation materials are produced with a vapor barrier applied on one side. If the insulation does not have such a vapor barrier, a separate one can be installed.
A vapor barrier is designed to prevent moisture problems in exterior walls and ceilings, as well as floors that face unheated areas, due to condensation of water vapor that passes through those surfaces. In order to be effective, the vapor barrier must be facing the heated area rather than the cool, unheated one.
In addition to the necessary insulation of the building shell (insulate all exterior walls, ceilings and floors), all hot-water pipes, as well as heating and cooling ducts that pass through unheated portions of the house (crawl space, garage or unfinished attic) must be insulated. Due to increasing fuel costs, one or two inches of insulation wrapped around ducts in unheated areas is considered minimal for most areas, and additional insulation can generally be justified.
The condition of your home insulation must be checked regularly for any loose, torn or missing sections, and if there are any exposed duct joints they should be checked to see if they are sealed tightly. When the ducts are used just for air conditioning or serve a double function, such as heating and air conditioning, the outside of the insulation should be covered with a vapor barrier to prevent condensation. If the ducts are used just for heating, a vapor barrier is not necessary. If there is a vapor barrier on the ducts, check its condition for torn and missing sections and ensure all joists are tightly sealed.
Moreover, if the domestic hot water is produced in a tank-type water heater located in an unheated area, make sure the tank is covered with an insulation jacket. Tank-type water heaters are usually insulated by the manufacturer, however by installing an outer insulation jacket you will further reduce heat loss and thereby minimize the energy consumption.
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