Should I vent my attic, and how do I do it?

Step 1: find out what you have

• From outside, look for soffit vents, a ridge vent, box vents, turbines, gable vents or a power fan.
• From the attic on a sunny day, look for daylight at the eaves and at the ridge or vents, and check whether insulation is stuffed against the eaves.
• Note warning signs: dark stained decking, rusty nails, damp insulation.

Step 2: fix intake first

Install baffles in the rafter bays at the eaves, pull insulation back from the soffit vents, clean painted over vents, and add soffit vents where the soffit is solid. If there is no soffit, an edge intake vent can go in at the bottom of the roof during a reroof.

Step 3: pick one exhaust

A ridge vent if the ridge is long enough, otherwise static vents grouped near the peak. Remove or block competing exhaust such as gable vents and old power fans so air flows from the eaves to the top.

Step 4: stop moisture at the source

Route bath fans and the kitchen hood outdoors through dedicated caps, and seal ceiling penetrations.

Cost reality

A box vent or a length of ridge vent is a modest material cost, but roof access, cutting, flashing and shingle repairs make up most of the price. If the roof is near the end of its life, fold ventilation into the replacement. See roof ventilation basics and signs you need a new roof.