Q. I am improving the attic ventilation in a 30-year-old two-story house in Virginia. My plan is to install soffit vents and insulation baffles. The attic has gable vents with thermostatically controlled fans. Do I have to install a ridge vent, or are the gable vents adequate? What advice shall I give the owners about the fans?
A.Bill Rose, architect and building researcher at the University of Illinois Urbana-Champaign, responds: There are four purported reasons to vent an attic space. The first is moisture control. Moisture control matters in the northern states, but in the humid South, only carpetbaggers would say that venting is necessary for moisture control.

The second reason for venting attics is to reduce ice dams, which are not a problem in Virginia. The third reason is to enhance the service life of asphalt shingles. How much effort and expense are you ready to put out so that the roof lasts 22 years instead of 20 years? (Use your own estimates of how long shingle roofs last — these are my personal guesses based on my own roof.)

The fourth reason is for comfort and savings during the summer cooling period. In your case, judging from the presence of a thermostatically controlled fan, I would guess that this is the main reason — to keep the attic air temperature as cool as possible. If it’s comfort and savings you want, ceiling insulation comes first. The gable fans might actually be counterproductive, since they might be sucking good air-conditioned air out of the house and into the attic. If there is ductwork in the attic, try to relocate it into the conditioned space, or at least correct any leaks or poor duct insulation.

Once you’ve sealed all of the openings that lead from below into the attic, corrected the ductwork, and installed a nice thick blanket of insulation in the attic, then one venting strategy is about as good as any other. Gable venting and ridge venting are both fine. Soffit venting with baffles is fine. Combinations are fine. If parts of the roof have a lot of venting and other parts have little or none, most would agree that that’s fine too. Power venting, however, is noisy and expensive.