...your kitchen exhaust fan very often. In fact, many people don't understand both reasons why the fan is important. Sure, most of us "get" the need to remove cooking odors. But more importantly, cooking can release lots of moisture into the air in your home. Amounts of moisture that are both unhealthy and bad for your home.
Properly vented kitchen exhaust fans have a duct that takes the moisture directly outside the home. Not merely to the attic, where the moisture can collect and damage the roof. Please note-if the only exhaust ventilation for your kitchen is via your microwave oven, some microwaves are designed to simply draw air into the vent, have it pass through some type of filter to cut down on the smell, and then return it to the kitchen. This does little to reduce moisture.
Talk to your contractor. Insist the kitchen exhaust fan be ducted outdoors.