Insulation: The Facts Part 5
Confused about R-values, rolled or blown-ininsulation, vapor barriers and other insulation terms? This series of stories,adapted from the U.S. Department of Energy "InsulationFact Sheet" explains the ins and outs of home insulation -- and may helpyou save significantly on your heating and cooling costs.
Once you have located the areas in your house requiring insulation, and havedetermined what R-value is needed, you will need to decide what type to buy.Some types of insulation require professional installation, and others you caninstall. You should consider the several forms of insulation available, theirR-values, and the thickness needed. Remember, for a given type and weight ofinsulation, the thicker it is, the higher its R-value. The basic forms ofthermal insulation are summarized in a chart in Part2 of this series. Here is some additional information.
|Basic forms of thermal insulation|
Blankets, in the form of batts or rolls, are flexible products made from mineral fibers. They are available in widths suited to standard spacing of wall studs and attic or floor joists. Continuous rolls can be hand-cut and trimmed to fit. They are available with or without vapor retarder facings. Batts with a special flame-resistant facing are available in various widths for basement walls where the insulation will be left exposed.
|Blown-in loose-fill insulation includes loose fibers or fiber pellets that are blown into building cavities or attics using special pneumatic equipment. Another form includes fibers that are co-sprayed with an adhesive to make them resistant to settling. The blown-in material can provide additional resistance to air infiltration if the insulation is sufficiently dense.|
Foamed-in-place polyurethane foam insulation can be applied by a professionalapplicator using special equipment to meter, mix, and spray into place.Polyurethane foam can also help to reduce air leaks.
|Rigid insulation is made from fibrous materials or plastic foams and is pressed or extruded into board-like forms and molded pipe-coverings. These provide thermal and acoustical insulation, strength with low weight, and coverage with few heat loss paths. Such boards may be faced with a reflective foil that reduces heat flow when next to an air space.|
|Reflective insulation systems are fabricated from aluminum foils with a variety of backings such as kraft paper, plastic film, polyethylene bubbles, or cardboard. The resistance to heat flow depends on the heat flow direction, and this type of insulation is most effective in reducing downward heat flow. Reflective systems are typically located between roof rafters, floor joists, or wall studs. If a single reflective surface is used alone and faces an open space, such as an attic, it is called a RADIANT BARRIER. Radiant barriers are sometimes used in buildings to reduce summer heat gain and winter heat loss. They are more effective in hot climates than in cool climates. All radiant barriers must have a low emittance (0.1 or less) and high reflectance (0.9 or more).|
|Use determines type of insulation|
The type of insulation you use will be determined by the nature of the spacesin the house that you plan to insulate. For example, since you cannotconveniently "pour" insulation into an overhead space, blankets, sprayor board products, or reflective systems are used between the joists of anunfinished basement ceiling.
The most economical way to fill closed cavities infinished walls is with blown-in insulation applied with pneumatic equipment orwith foamed-in-place polyurethane foam. Theinsulation types table in Part 2 provides a concise summary of the appropriate applications for the varioustypes of thermal insulation.
It is important to know that the different forms of insulation can be usedtogether. For example, you can add batt or roll insulation over loose-fillinsulation, or vice-versa. Usually, material of higher density (weight per unitvolume) should not be placed on top of lower density insulation that is easilycompressed. Doing so will reduce the thickness of the material underneath andthereby lower its R-value.
In cold climates, some low-density loose-fill insulation allows air tocirculate between the top of your ceiling and the attic. This air circulationcan decrease the effective thermal resistance of the insulation and may besignificant for regions with more than 5000 heating degree days, or north of aline running from New York to Pittsburgh to St. Louis to Topeka to Santa Fe toReno and up to Portland, Oregon. You can eliminate this air circulation bycovering the loose-fill insulation with a blanket insulation product or with ahigher density loose-fill insulation.
|Check the label before buying|
No matter what kind of insulation you buy, check the information on theproduct label to make sure that the product is suitable for the intendedapplication. A good insulation label should have a clearly stated R-value, andinformation about health and safety issues. An informative label should state:
- The type of insulation material
- The R-value (measured at 75F)
- The types of spaces that can be insulated
- Safety precautions in application and use, including any fire-hazard related restrictions
- The quantity in the package
- The name and address of the manufacturer or distributor
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