After purchasing a 1940s stone cottage near the base of Mohawk Mountain Ski Area in Connecticut, Sarah Jefferys, a New York–based architect, renovated it as a second home, which she and her family share with that of a lifelong friend who is a co-owner. The surprising transformation not only brings the English-style cottage up to 21st-century standards—it includes an unexpectedly modern wing.

The new construction encompasses a combined ground-floor kitchen and dining room in a discrete cypress-clad volume big enough to accommodate both families, should their stays overlap. Sleeping quarters occupy the addition’s second level, which cantelevers to the southeast. “Somewhat inspired by dogtrot houses, which had a central breezeway dividing the house,” Jefferys says, the kitchen abuts the original house’s den to link new and old.