Vapor barriers and air conditioning ductwork

Air Conditioning and Heat Pumps · Thermostats · printed page 224 (PDF page 225)

Book index entries

Vapor Barriers and Air Conditioning Ductwork Ducts – and Vapor Barriers for Air Conditioning Vapor Barrier – and Air Conditioning Ductwork Duct System Ducts – System for Air Conditioning

Text in the illustration

attic
A/C duct
insulation
vapor barrier
cross section
note: insulation size exaggerated for clarity typically, 1-1/2" to 2" would be used
warm, humid air in an attic (during the summer) could condense on cool A/C ductwork, so the vapor barrier on the ductwork has to be on the "top" of the insulation

Generated explanation

A cross section shows an insulated air-conditioning duct in an attic framed with sloping roof members above an insulated ceiling. The round duct is surrounded by insulation, with a vapor barrier on the outside of the duct insulation. The vapor-barrier callout also points to a layer beneath the ceiling insulation. An annotation explains that warm, humid attic air can condense on cool ductwork, requiring the duct vapor barrier to be outside the insulation. A note states that the illustrated duct insulation thickness is exaggerated for clarity and that typically 1-1/2 to 2 inches would be used.

Components

air-conditioning duct duct insulation duct vapor barrier ceiling insulation ceiling vapor barrier roof framing ceiling framing wall framing

Materials

wood framing thermal insulation vapor-barrier membrane

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