Bathroom Fans and Moisture in Tacoma's Damp Climate

Why bathrooms here grow spots

Cool walls, damp air and long showers mean condensation. When a bathroom has no fan, a weak fan, or a fan that vents into the attic, that moisture settles on the ceiling, in the corners and on the window frame. Mildew follows.

The attic problem

Older fans are sometimes ducted only into the attic space, or not ducted at all. Warm, wet air then condenses on cold roof sheathing. Over time that can lead to stained sheathing and rot. On our remodels, the fan goes to the outside.

Sizing and placement

Fans are rated by how much air they move. Bigger rooms and bigger showers need more. Placing the fan near the shower, not over the door, clears steam much faster. Quieter fans also get used more, which matters more than the rating.

• Put the fan close to the shower
• Use smooth, short duct runs to an exterior cap
• Add a timer or humidity switch so it runs long enough
• Leave a gap under the door so make-up air can enter

Windows are not enough

A window helps in summer. In a Tacoma January, few people open it after a shower. A fan you do not have to think about works year-round.