We here at Just Housing are big proponents of nailbase panels because their benefits are many. They provide continuous exterior insulation—especially useful for energy retrofits—which improves thermal performance by slowing heat loss and reducing thermal bridging, resulting in energy and monetary savings; they provide sheathing and foam insulation in a single product; and they are cost-effective, widely available, and flexible for use in different applications. But installing windows in walls with nailbase insulation presents unique conditions. Here we will explain our method for detailing the four control layers at the windows.

Window considerations

Windows are one of the most complex installation details in a high-performance home. The joints, changes in planes, and transitions between materials—repeated over and over again at every window—can challenge any designer’s or builder’s ability to effectively manage water, air, vapor, and thermal performance, while ensuring window functionality.

In our cold climate (we work in Climate Zones 6 and 7), we almost always specify tri-pane glazing with an overall unit U-factor of <.23. We specify insulated fiberglass frames because they provide durability and sufficient thermal resistance, and they are widely available in North America. We also typically specify a window with nailfins, in large part because this is what the tradespeople in our region are most familiar with, and are most comfortable installing. These specifications alone, however, will not guarantee effective performance.

The success of windows hinges on their integration with the four control layers and how effectively the stage is set for project practitioners to successfully execute them. Below, we outline how Just Housing integrates windows into the control layers while balancing performance, cost effectiveness, simplicity, and comfort.

Beginning at the rough

The window rough opening is where many of these strategies intersect. We use box frames made from 2x lumber ripped…