The very innovative UNDEReve Vent by DeFlect-O Corp has two dampers or flappers keeping the outside air from re-entering the house yet provides a fabulous, attractive and efficient means to terminate the exhaust when running in the attic. Why penetrate the roof when this soffit vent solution exists. Works with exhaust fans as well as the dryer. It is available in some Home Depots and Lowe's and also available here in our shopping cart under accessories. accessories.