Duct Internal Condensation → Insulation Delamination → Ceiling Water Leak

Question

Accepted Answer

Insufficient insulation thickness — duct surface cools below dew point during cooling operation. Check: Touch duct exterior by hand — cold and damp or beading water confirms condensation. IR camera to find sections where surface temperature is below indoor dew point (12–16°C). Measure current insulation thickness (below 25 mm is at risk) What to do: Add XLPE foam (expanded polyethylene) ≥25 mm over existing insulation — fully seal joints with aluminum tape → add hangers at sagging sections (1.2 m intervals) → drill drain hole at low points and protect ceiling with drain panel Insulation joint gaps — inadequate taping at glass wool or XLPE joints. Check: Check if condensation is concentrated at specific spots — concentrated condensation at joint tape gaps. Disassemble insulation at affected areas to visually inspect joint condition What to do: Fully remove existing tape at joints → re-tape seamlessly with aluminum foil tape (≥50 mm overlap) → monitor all sections for condensation recurrence Insulation aged 5+ years — water repellency lost, delamination after moisture absorption. Check: Inspect insulation appearance — moisture absorption (darkening, heavier feel), peeling, sagging. If installed 5+ years ago, consider full replacement What to do: Full replacement of aged insulation — XLPE ≥25 mm, fully seal joints with aluminum tape → establish 5-year cycle plan for water repellent recoating or insulation renewal

Duct Internal Condensation → Insulation Delamination → Ceiling Water Leak

Likely causes

Insufficient insulation thickness — duct surface cools below dew point during cooling operation

Insulation joint gaps — inadequate taping at glass wool or XLPE joints

Insulation aged 5+ years — water repellency lost, delamination after moisture absorption

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