ebuild Guide to Building Insulation Specifications

A highly-insulated house was once a hallmark of high-end construction, but now every house must be carefully insulated to minimize heating and cooling costs. Upgrading insulation beyond the minimum standards increases comfort, reduces heating and air conditioning costs, and enables the use of smaller, less expensive furnaces, cooling equipment, and duct work.

A building looses and gains heat in three ways:

The thickness of a material is a critical factor when it comes to reducing conduction losses. As for convection losses, reductions relate primarily to how the insulation is installed. Some materials readily block convection losses, while the ability of others depends largely on the care with which they are installed. Insulation materials with a foil surface can be used to block radiant heat gain. The amount of insulation required in a house varies greatly by region. Generally, local codes determine the minimum R-value but leave the choice of material to the builder.

Key Specifications

R-value--This figure is a measure of a material's ability to resist heat transmission by way of conduction. The higher the R-value, the more a given thickness of material can resist the transfer of heat.

Thickness--The R-value of a material is cumulative by its thickness; if you double its thickness, you double its R-value.

Width--Batts of a specific width fit between a given O.C. (on center) spacing of studs or joists. The nominal width of insulation typically equals the O.C. spacing of framing, but the actual width is approximately 1-1/2 inches less than that. In the case of rigid sheets, the width (and length) determines how quickly the product can be installed over a given area.

Facing--Whether batts are faced or unfaced affects how they are installed and whether a separate vapor retarder will be required.

Even materials with a high R-value won't make a house comfortable if they are installed improperly--convection losses can dramatically reduce the effectiveness of an insulating layer. It's also important to consider how insulation performs over time. Some types of rigid sheet insulation, for example, lose insulating value as the material ages. Loose-fill insulation becomes less effective as it settles, and batts loose insulating value if they are compressed. Be sure to consider the initial R-value of a product as well as its in-place or aged R-value.

* These ranges include the effects of aging and settling. Manufacturer's R-value figures will vary and may be higher.

Types of Insulation Materials

There several ways categorize the wide variety of insulation products. They can be considered by cost, material, R-value, or even by how green they are. However, builders usually are more concerned about how easily the material can be installed or how suitable it is for a particular application. With that in mind, there are four basic types of insulation: batts, loose fill, rigid sheets, and sprayed or blown insulation.

Batt Insulation--Batt insulation is the most common form of residential insulation, in part because it is widely available, easy to install and relatively inexpensive. Batts are long strips of high-loft insulation cut to a particular width. They may be purchased in the form of rolls that can be cut to length, or in bundles of pre-cut lengths. Batt insulation can be installed in walls, ceilings and floors, but isn't suitable where it might be compressed or where it will be in contact with moisture. The material itself is most often made of fiberglass but other materials are available, including cotton, natural wool, and mineral wool.

Batt insulation can be purchased with or without a facing. The facing, usually made of foil, Kraft paper or plastic film, serves as a vapor retarder to prevent moist air vapor generated inside the house from reaching the insulation. Also, tabs along the edges of the facing enable the batts to be stapled to studs or joists.

Unfaced insulation is sometimes referred to as friction-fit insulation and is pressed between framing members. After installation in a wall, a separate vapor retarder must be applied over the entire insulated area before the installation of drywall or other wall coverings. Unfaced batts are also used in attics to add thickness to faced batts. Some contractors, for example, insulate between attic floor joists with faced batts, and then run a layer of unfaced insulation at 90-degrees to the first.

Batt insulation comes in various thicknesses to suit typical wall and ceiling construction, and in widths suited to standard stud and joist spacing. In terms of R-value, batts range from R-11 to R-38.

Loose Fill Insulation--Loose fill insulation is usually supplied in bags or bales and is poured or blown into place using a specialized blowing machine. Loose fill insulation is suited primarily for unfinished attics, closed wall cavities and cores of masonry block. Loose fill insulation is often used in attic floors where various HVAC pipes and wiring would make it difficult to install batt insulation. A separate vapor retarder should be installed. Materials used for loose fill insulation include shredded fiberglass, mineral wool, vermiculite, and cellulose-based products.

Rigid Insulation --Rigid insulation is manufactured as sheets or panels which often feature a reflective radiant barrier surface on one or both sides. These thin panels pack more R-value into a smaller space than many other types of insulation, but the inflexibility of the product makes it unsuited for use between studs or joists. It is primarily used as a non-structural sheathing, backing layer for siding, or as an insulating layer on the outside surface of foundation walls.

Several types of rigid insulation are available:

Sprayed and Blown Insulation--Sprayed and blown insulation products readily fill cracks and gaps that might otherwise become paths for air infiltration. Sprayed insulation is applied as a wet material that must cure or dry before being covered, and can be installed in walls, ceilings, and floors. Builders often turn to this type of insulation when no other type can be installed. Blown insulation, on the other hand, is applied dry and is most often used to insulate closed wall and ceiling bays. Both products call for specialized application equipment.

Various fibrous and non-fibrous materials can be sprayed into wall and ceiling cavities. Fiber-based products include cellulose, fiberglass, and mineral wool. When adhesive is mixed with the fibers, the insulation readily sticks to surfaces.

Non-fibrous sprayed insulation starts as a liquid that contains a polymer and a foaming agent. One kind, isocyanurate, is an open-cell product while the other, polyurethane, is a closed-cell product. Both materials are sprayed into open wall and ceiling cavities before finished wall surfaces have been installed. Exposed to air, the liquid expands dramatically to seal and fill stud and joist bays. After the insulation has cured, excess material must be sliced off flush with the surface of the framing. Closed-cell spray insulation typically has a higher R-value than open-cell spray insulation.

The costs of insulating a house depends on factors such as the R-value required by local codes, and whether or not the insulation requires a separate vapor barrier. In general, though, the least expensive option is usually fiberglass batt insulation.

Installing insulation is a job in which good craftsmanship pays off in heating and cooling savings. Whatever the material, it is critical to make sure that the material thoroughly fills all the wall and ceiling cavities. There should be no gaps between the insulation and the framing, and no gaps around electrical boxes or plumbing penetrations. Gaps form a ready passage through which heat can escape.

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