INFORMATION SERIES: Insulation Conditions

Insulation is used primarily to reduce the rate of heat transfer from areas of high temperature to those at a lower temperature. The ability of a material to slow this movement of heat is referred to as its thermal resistance or R-value. Insulation materials are rated based on this R-value; the higher the R-value the longer it takes for heat to move through the material. In cold weather insulation retains the heat within the house; in warm weather it reduces the rate at which the exterior heat moves to the cooler interior. Insulation affects all three modes of heat transfer - conduction, convection and radiation.

To be effective, the insulation must be the proper type, have adequate thermal resistancy for the location 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 placement should be according to building code guidelines and
manufacturer recommendations.

Since the mid 1970s, insulation of new homes has been standard; the retrofit of older homes with insulation has become desirable due to ever increasing fuel costs. Homes constructed prior to 1970 generally had minimal amounts of insulation; prior to 1940, insulation was rare. In general, insulation should be applied in all areas or cavities between 
conditioned (heated or cooled) and unconditioned spaces

The amount of insulation required varies with the location in the structure and the geological area of the house. Each type insulation has a different R-value per inch of thickness. In general, the more extreme the temperatures the higher the recommended R-value. R-19 is the minimum ceiling insulation for all areas; R-11 the minimum in the exterior walls. Some typical recommended ceiling insulation amounts are indicated on the map. To find out the exact recommended R-value for your specific area, consult with your 
local building department.

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. Incidentally, compressing 6" of insulation into a 3" space does not provide the rated thermal resistance. Due to the compaction, there is greater heat loss through conduction 
than if 3" of insulation is placed in a 3' space.

All the types and characteristics of insulation cannot be readily determined within an existing structure due to the possible mix of insulation materials, the inability to observe insulation due to structural elements and other factors. While insulation materials may be identified during a visual inspection, the actual makeup of any insulation can only be determined by laboratory analysis.

Heat producing recessed light fixtures and chimneys should not be tightly surrounded by insulation. Generally a 2-6 inch clearance is required, unless labeling specifically states otherwise. Adequate ventilation around the unit should be provided and maintained. Cathedral ceilings, finished attics 
and attics with blocked or insufficient vent provisions are particularly prone to excessive heat and/or moisture build-up.

The HouseMaster Technical Staff recommends that when installing insulation materials, homeowner should follow manufacturer instructions. Wear appropriate mask, gloves and other protective clothing. Do not forget to insulate over the access doors to attics or unconditioned spaces. Also, check visible insulation periodically for damage from moisture, squirrels, storage or other factors. 

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, fiberglass, (etc.). In certain situations, or if recommended, remedial measures will be required. In most cases, however, minimizing disturbance or contact with the insulation material is a feasible approach to minimize potential concerns. Research indicates that individuals react differently to insulation materials; any contact by hypersensitive individuals should be avoided. If any particular concerns exist regarding any insulation, independent laboratory analysis should be considered.

Vapor retarders minimize the flow of water vapor into and through insulation. Moisture trapped in insulation, or passing through it and contacting a cold surface, may condense and reduce the insulation's effectiveness or cause structure damage. Vapor retarders should be installed on the warm side of an insulated area in cold climates. Only one vapor barrier should be installed. A second layer above or adjacent to another may allow the entrapment of moisture and consequential damage.

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