PRINCIPLES/DEFECTS
Insulation System Defects
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Discontinuity in insulation system design
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Voids and gaps
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Unsupported insulation
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Compression by fasteners and other elements
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Fibrous insulation exposed to air spaces
.
Poor fitting batt insulation
Defects in the envelope insulation system include both discontinuities in the insulation layer and
arrangements of the insulation which decrease its effectiveness. Envelope performance is then
degraded by the increased heat transfer rate and the potential for condensation when components
in contact with moist interior air attain colder temperatures than anticipated. Such defects include
insulation system design details which incorporate discontinuities in the insulation layer, voids or
gaps in insulation systems due to improper installation or deterioration of the insulation material,
movement of the insulation due to a lack of adequate physical support, and compression of
insulation caused by fasteners or other building elements.
The thermal effectiveness of fibrous insulation is greatly reduced when the insulation is installed
with air spaces or cavities on one or both sides of the insulation layer, due to convective airflows
through and around the insulation. This defect can be avoided by designs in which the insulation
completely fills the cavity or which employ a continuous air barrier on the cavity side of the
insulation.
Batt insulation may be associated with performance problems when the batts are poorly installed or
do not fit well within the available space. These include arching or air channels caused by
oversized batts, gaps due to undersized batts, and gaps and air channels caused by poor
installation of batts. The existence of gaps or air channels within the insulation system and the air
movement through these spaces severely degrade the effectiveness of the insulation.
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