1. Strapped Ceilings Attach the air barrier material to the unde…
1. Strapped Ceilings Attach the air barrier material to the underside of the ceiling joists or trusses. Strap the ceiling beneath the air barrier with ripped 2×4 or 2×6 material, fastened with structural screws. Then cross-strap with 1×3 strapping. Fasten the wiring to the sides of the 2x strapping, tight to the ceiling, and fasten the drywall to the 1×3 strapping. Be careful not to poke holes in the air barrier.
Harry Whitver
2. Hallway Plenums Attach the air barrier material to the unders…
2. Hallway Plenums Attach the air barrier material to the underside of the ceiling framing. Frame a dropped ceiling with 2x4s, running from wall to wall. This creates a chase large enough to contain ductwork, wiring, plumbing, or even a small air handler and indoor coil for a mini-split heating and cooling unit, keeping all that equipment out of the insulated attic.
Harry Whitver
3. Strapped Walls Apply a smart vapor control membrane to the fa…
3. Strapped Walls Apply a smart vapor control membrane to the face of the stud wall. Strap the walls with 2×4 material or ripped 2×6 stock, run horizontally. This creates chases for wiring inboard of the air and vapor control membrane. If you need more room, you can frame a whole second wall inboard of the air barrier.
Harry Whitver
4. Baseboard Raceways Here's a trick to provide an isolated wiri…
4. Baseboard Raceways Here's a trick to provide an isolated wiring chase without having to fur out the whole wall: build a raceway into the space behind baseboard molding. In a more formal room, wainscot wall paneling can be installed similarly, with an air space that provides lots of room for wiring. Either way, apple the air and vapor control layer membrane to the wall before furring out.
The house of the future is airtight. Examples: the Passive House standard calls for 0.6 air changes per hour at 50 pascals depressurization (ACH50), while Efficiency Vermont’s standard for new homes is 1.0 ACH50.
Even regular building codes are getting tougher. The 2012 International Energy Conservation Code (IECC) requires 3 ACH50 in cold regions, 5 ACH50 in milder climates. Many states are not enforcing that, however—mostly because some builders say that 3 ACH50 or 5 ACH50 is too strict (or too costly).
But if 3 ACH50 is too tough, how are Passive House builders doing five times better? One strategy they employ is ensuring the airtight shell is never compromised by wiring, plumbing, or mechanicals. The trick is to create chases that isolate those services from the insulation and air barrier. Tedd Benson, founder of Bensonwood Homes in Walpole, N.H., calls this “disentangling” the building elements.
This approach keeps the air-pressure control layer intact as you finish out the house. It also allows future owners to modify the plumbing, wiring, or HVAC as technology advances, or when their needs change—without risking the performance of the building structure or the insulated airtight envelope.
