Why does an uninsulated louver blank-off panel sweat?

Field answer

A blank-off panel at an exterior louver can act like a cold plate. If the indoor side is warm and humid while the exterior metal is cold, water can form on the panel and drip into the wall cavity.

Check whether the inactive louver section is single-skin, uninsulated, or poorly sealed. The usual recovery is an insulated double-wall blank-off panel or approved insulated closure detail, with sealed edges and a protected drainage path.

What to check first

• Look for sweating on the room-side face of the blank-off.
• Check whether the panel is insulated or just one sheet of metal.
• Inspect the perimeter seal and wall cavity staining.
• Confirm the active/inactive louver layout on the drawings.
• Use approved insulated closure material and keep drainage paths open.

Why it matters

Thermal bridging can rot wall cavities, stain finishes, and create mold risk.

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Final direction belongs to the foreman, approved drawings/specs, manufacturer instructions, pressure/material schedule, employer policy, and AHJ/code requirements.