Proper ventilation is very important in any bathroom. Without good ventilation, moisture is trapped and causes damage to building materials. This results in unpleasant odors and the possible growth of harmful bacteria, such as mildew and mold.

A bathroom needs two types of ventilation:

> a drain waste vent system and an air ventilation system. Both play an important role in keeping the bathroom healthy and comfortable. A drain waste vent system releases gases and odors through pipes by carrying them through the roof of the house. This system allows ugly odors to escape from the home and it helps to control the water seal in the drain pipe traps under the sink. This keeps sewer gases from backing up into your bathroom.

> Every home everywhere is required to provide some kind of air ventilation system. There are two main ways to provide ventilation — with a window that can open to the outside or with a mechanical ventilation system. Even though building codes generally require only one or the other, it is fairly commonplace today to find bathrooms built with both a window and a vent fan.

Mechanical ventilation systems are easy to install, are relatively inexpensive, and are often more effective and efficient than opening a window. To choose a ventilation fan, just select a fan with the capacity to completely replace the air in the bathroom at the rate of about ten times per hour. Vent fans are rated in terms of the number of cubic feet of air exchanged per minute. If you are building or remodeling a large bathroom, you might find it advisable to install more than one vent fan (toilet, tub, shower areas).