Core TradesQuestion 158 of 700
In a heating-dominated (cold-winter) climate, a vapor retarder in an exterior wall is generally installed on which side of the insulation?
a.The exterior (cold) side
b.Both faces of the insulation
c.The interior (warm-in-winter) side
d.It is omitted entirely
Explanation
In a cold climate the warm, moist interior air moves outward, so the vapor retarder goes on the interior (warm) side to stop moisture before it reaches the cold sheathing where it would condense. Placing it on the cold side, or on both sides, can trap moisture inside the wall and cause rot.
Law Reference: 2025 CA Residential Code §R702.7Practice all 700 questions free — no signup required.
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