Conventional wood-framed walls perform many functions. Exterior walls are supposed to support the roof load, resist racking, and provide insulation. They must also provide space for routing electrical cables and (in some cases) plumbing pipes or even ductwork. If the walls are built properly, they should also include an air barrier.
Timber-frame manufacturer Tedd Benson has criticized our conventional approach to building walls. He calls these multipurpose walls “entangled,” and he proposes a new approach to wall building — one that begins by disentangling the various functions of a wall.
According to Benson, “Wires and fixtures should be separated from high-performance wall and roof systems whenever possible. [At Bensonwood Homes,] we add a mechanical chase layer to our walls always, and to our roof panels when there is a heavy mechanical demand in that area. Otherwise, we have dedicated chases at the building peak, at the eave and other strategic locations when necessary. The point is that after sealing a building…, we need to also make changes and upgrades easy and provide a path other than one that violates the integrity of the envelope.”
There are many ways to disentangle utilities from the other functions of a wall. Approaches range from timber-framing, to PERSIST construction, to the use of Larsen trusses, to a variety of techniques adopted by Passivhaus builders in Europe. One element shared by many of these techniques is the service cavity.
A service cavity (installationsebene in German) is a “wall-within-a-wall” — a secondary wall on the inside of an exterior wall. It can be framed conventionally, using vertical 2x4s or 2x3s, or it can be created by installing horizontal 2×2 or 2×3 strapping. The main purpose of a service cavity (also called a “service core”) is to provide room to run wiring, plumbing, and ductwork.
Most proponents of service…