Insulation
Insulation materials are used in a house primarily to reduce the rate of heat transfer from areas of high temperature to areas at a lower temperature. The ability of a material to slow this movement of heat is referred to as its thermal resistance value (or R-value). Insulation materials are labeled based on their R-value; the higher the R-value the longer it takes for heat to move through the material. In cold weather, insulation helps retain heat within the house; in warm weather it reduces the rate at which outdoor heats moves into the cooler interior. Insulation has an affect on all three forms of heat transfer – conduction, convection and radiation.
There are many different insulation products. To be an effective insulator, insulation materials must be the proper type, have an adequate thermal resistance value, and be properly installed. Most building codes specify the minimum insulation required (or maximum heat loss or gain allowed through a particular building component). Insulation should be installed according to building codes and manufacturer recommendations.
Since the mid 1970s, the full insulation of new homes has been standard practice; the retrofit of older homes with insulation is desirable due to ever increasing fuel costs. Houses constructed prior to 1970 generally have minimal insulation; to find any significant insulation in houses built prior to the 1940s is rare, unless a major retrofit job was completed. In general, insulation should be installed in the house envelope and in all areas or cavities of the house structure that serves as a barrier between the conditioned (heated or cooled) living areas and unconditioned spaces or outdoors.
Building and energy codes address heat loss and gain issues, and establish minimum insulation requirements to limit energy costs. The amount of insulation required varies with the geographic location of a house and where in the house it is used. Each type of insulation has a different thermal resistance per inch of thickness. The more extreme the temperatures, the higher the recommended R-value for insulation. To find out the current insulation requirements for your specific area, consult with your local building department or electric/gas utility company.
The greatest benefit from insulation is usually attained with the first 3-6 inches. Greater amounts are undoubtedly beneficial; however, the payback in fuel saving diminishes as more insulation is added. The attic (or roof) is the most important area to insulate. Insulation with an R-19 value is generally the minimum ceiling insulation for any region; R-11 is the minimum for exterior walls. Colder climates will require much higher levels. Incidentally, compressing 6 inches of insulation into a 3-inch space does not provide the listed thermal resistance, as compaction results in a greater rate of conductive heat transfer. In addition to making sure all areas of an attic floor are covered and the insulation isn't compacted, it is also important to make sure the access doors between the living areas and attics or other unconditioned spaces are insulated.
All the types and characteristics of insulation used within an existing structure cannot be readily determined because of the possible mix or contamination of insulation materials and the inability to visually observe installed insulation due to structural elements and other factors. Although not required, certain representations regarding observed insulation materials may be made as part of a home inspection; although, the actual makeup of any insulation can only be determined by laboratory analysis or confirmation by the manufacturer.
When installing or working with any insulation materials, manufacturer instructions should be followed. Most insulation materials consist of elements, either in whole or part, which are potential or verified health or environmental contaminants (e.g., asbestos, urea formaldehyde, vermiculite, fiberglass, etc.). In most cases, by not disturbing or making contact with installed insulation materials, potential concerns will be minimized. In other situations, particularly if installing or removing insulation, or when a house is undergoing renovations, special precautions should be taken to ensure that conditions are not made worse. At the very least, wear an appropriate mask, gloves and other protective clothing.
If actual hazardous insulation materials or conditions are reported or suspected, for example, the presence of friable asbestos insulation, remediation by qualified specialist is recommended. Individuals react differently to insulation materials; any insulation contact by hypersensitive individuals is best avoided altogether. If any particular concerns exist regarding the makeup of any insulation, independent laboratory analysis and/or assessment by a qualified specialist should be considered.
Vapor retarders are generally installed with insulation to minimize the flow of potentially damaging water vapor into and through the insulation. Moisture trapped in insulation, or passing through it and then contacting a cold surface, may condense and reduce the insulation's effectiveness or cause structure dam-age. In cold climates, it is important for a vapor retarder to be installed on the warm side of any insulated roof, or wall, ceiling, or floor assembly between the exterior and interior conditioned areas. Only one vapor retarder layer should be installed in an assembly; a second vapor retarder placed above or adjacent to another may allow the entrapment of moisture and consequential damage.
Heat-producing recessed light fixtures and chimneys should not be tightly surrounded by insulation. Adequate ventilation around the unit should be provided and maintained at all times. Generally a 2-6 inch clearance is required, unless labeling specifically states otherwise. Cathedral ceilings, finished attics and attics with blocked or insufficient vent provisions are particularly prone to excessive heat and/or moisture build-up, and possible collateral damage from insulation or vapor retarder defects. Where visible, insulation materials and vapor retarders should be periodically checked for signs of damage, including that caused by stored items, moisture, rodents, and other pests or factors.
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