The presentation will discuss the design process for analyzing and constructing a building envelope to meet aggressive air-sealing goals for new and renovated commercial and institutional projects in cold climates. Example details from three case study buildings will be shared with a central focus on decisions, changes, best practice guidelines, thermal analysis, lessons learned and specific challenges encountered during the construction process. The final details that evolved from focused scrutiny and close collaboration between the design and construction team will be presented for both the new construction example, The Middlebury South Village Professional Office building, as well as two renovation projects, the George D. Aiken Center at UVM and the Bennington Superior Courthouse and State Office Building. All three of these Vermont buildings achieved exemplary levels of low air-infiltration, with one achieving a rate of 0.06 CFM50/sq. ft of exterior surface area.