With today’s high cost of living and building, it is important to maximize a house’s every square foot. As a result, many of our clients want to take advantage of a “bonus space” over the garage. Not all designs suit this type of construction, but many do.

The space over a garage can provide flexibility to be an office, game room, guest suite, or even a self-sufficient VRBO or Airbnb rental. In terms of its construction, some builders say, “Just use attic trusses, install sheets of drywall, paint, and voilà, it’s done.” Sounds easy, and couldn’t cost more than a few bucks, right? Well, not exactly, but adding functional square footage without increasing the size of the home’s footprint is an attractive proposition. It just needs to be done right, and in a high-performance home, some additional detailing is required.

Insulating below a vented roof

Attic trusses are engineered to allow for an open, buildable space within the chords of the truss. Sometimes the floor system is built over the top of a beefed-up (say, 11-7/8-in. LVL) bottom chord; other times an independent floor system is framed. (These spaces can be a great place for a dormer to take advantage of a view from the second level.) It is important to remember that like the rest of the house, this roof-attic space requires venting—unless you plan to use a hot-roof, meaning unvented, strategy, which comes with its own set of pros/cons and cost implications.

On a recent project, the truss chord separating the interior space from the vented attic was a 2×4 vertical member. This member extended vertically from the floor level up to 7 ft., where it turned 45 degrees and…