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Mold & Moisture on Windows - Causes & Solutions

Heavy mold growth on window

mold single pane window

Condensation is typical on a single pane window. However, proper ventilation can often eliminate moisture buildup


water and mold double pane window2

Heavy condensation on a double pane vinyl window requires extremely high humidity levels.



Heavy condensation on window

Heavy condensation on a double pane window indicates high indoor RH

Project Report > Mold & Moisture on Windows


  • Adequate Ventilation Not Present
  • Recommended ventilation of residential homes should be between 0.35 and 0.7 air changes per hour (ACH).
  • Desired Ventilation Rate:  0.5 ACH (Air Changes per Hour)

Condensation on living room window


  • Improve ventilation by one of the methods listed below:
  • Install ducted HRV (Venmar Constructo 1.0) in the utility room with registers placed in accordance with the diagram above, and all ducting run through the attic space.


Moisture coming from kitchen window


  • Major condensation noted on window.
  • Kitchen range exhaust hood not ducted to the exterior.
  • Minor surface mold growth noted on window sill.
  • RH:61.3% Temp:53.8°F CO2:2718ppm CO: 0ppm


  • All condensation should cease once ventilation improvements have been enacted.

Living Room:


  • Major condensation noted on windows
  • Moderate surface mold growth noted on windowsills and casing
  • RH:60.1% Temp:67.7°F CO2:2761ppm CO: 0ppm


Condensation and growth on bedroom ceiling

  • No increased moisture content noted in building materials, except active condensation noted on ceiling.
  • Inspection with FLIR revealed major insulation defects in exterior wall.
  • Major condensation noted on windows.
  • Obvious dripping condensation noted on ceiling at exterior corner.
  • Significant visible mold growth noted on window sills and casings.
  • Moderate visible surface mold growth noted on ceiling at exterior corner.
  • Minor surface mold growth noted on baseboards at exterior corner.
  • RH:60.6% Temp:68.5F CO2:2786ppm CO: 0ppm


  • 110CFM Broan exhaust fan installed in this area.
  • Increased moisture content noted in baseboard and sheetrock immediately behind the toilet and adjacent to the shower.
  • Mold growth is likely present in this wall cavity.
  • Storage area sufficient to house an HRV located in this area
  • RH:57.9% Temp:69.2°F CO2:2840pm CO: 0ppm


  • Install splash-guard to prevent further water damage to the walls.
  • Address wet building materials.

 Laundry Closet:

  • 40CFM nutone exhaust fan in this area
  • Minor mold growth around the laundry exhaust fan.

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