Why Do Windows Fog on One Side of House & Not the Other?

Humidity

• Humidity is caused when water particles are present in the air. The degree of humidity can depend upon the amount of water in the region as well as the current weather. High humidity occurs during rainstorms and snowstorms or when heat causes the rapid evaporation of water from plants, crops, lakes and rivers. Indoor humidity is caused by warm room temperatures coupled with wet surfaces, leaks or a large number of houseplants. Window exteriors fog when outdoor humidity is high. Window interiors fog when household humidity is high.

Interior Window Fog

• Interior window condensations can occur in one area of a house and not another because of the window's location. Windows close to bathrooms, laundry rooms and kitchens are more likely to fog than those located in dryer areas of a home. Windows with heavy curtains are also more likely to fog because of insufficient airflow across the window surface. Plants also produce humidity through their pores as well as by any standing water found in pots of containers.

Exterior Window Fog

• There are several different reasons why some windows may exhibit more exterior fogging than other windows. Exterior window condensation can be caused by large outdoor landscape plants that have the potential to trap air and moisture against windows and buildings. Warm windows, such as those heated from the inside, are more prone to fogging than are cool windows. Sunlight will "burn off" fog. The sun heats the surrounding air, allowing moisture to circulate and free itself from window surfaces. Windows that experience direct sunlight are less likely to fog, as are windows in cool rooms and those without landscape plantings near them.

Considerations

• Control indoor humidity by using proper ventilation in high moisture areas or limiting the number of houseplants. Excess indoor condensation can be an indication of leaking pipes or a leaking roof. If ventilation does not adequately reduce the amount of condensation then inspect for leaking pipes and other sources of moisture. Outdoor condensation is reduced by cutting back landscape plants. Fog may build up in between the panes of some double-paned windows. This is caused by an insufficient seal between panes. Trapped moisture will not exit the panes and the windows will eventually need to be replaced.