WESTPORT, CONNECTICUT, residents Diane and Kevin Connolly and their two children have been retreating to Annisquam — a small village in Gloucester — during the summer for many years. Until recently, the house where they went to decompress was an “old, lightweight, single-story beach house,” says Tim Thurman of Rockport-based Treehouse Design Inc., the design/build firm the Connollys hired to create a lasting, durable home. Because the Connollys plan to retire to Cape Ann eventually, the house needed to be ready to withstand a wind-whipped North Shore winter, but it also had to be fun and casual enough for summering. So Thurman’s team collaborated with Watertown-based designer Sarah Wainwright to create interiors with a relaxed, beachy feel and to incorporate plenty of local materials.