Type 1B Multi-family

Jeremy, We have used blower door testing on several projects to verify that residential units were air sealed and tobacco smoke in one unit would not travel to adjacent units. This not easy to achieve in projects with light gauge metal framing. Wood framed buildings are a bit easier, but can still require additional diligence to seal penetrations. While wood studs can sometimes help create an air barrier between one stud bay and another, metal studs and joist all have openings for routing wires, etc. The effort is worthwhile: complaints from smoke odors passing between units can and do happen and are hard to fix. The air sealing also contributes to acoustic (and thermal) performance. Some typical problem spots: pocket doors, soffits, can lights, wet walls with many penetrations, bundles of wires, and tub/shower enclosures that don’t have wall board behind them. Common walls between dwelling units may have staggered studs, or RC channel like you mention, so electrical outlets facing one unit could have an air pathway to an outlet facing the other unit even if they are in separate stud bays. In some cases “putty packs” to seal outlets in common walls might be useful. One good reference is the EPA Thermal Bypass Checklist Guide used by LEED Homes, HERS raters and others: http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/TBC_Guide_062507.pdf One approach is to create a continuous air barrier with drywall at the common wall between units. This layer of drywall needs a small gap in the framing so is not interrupted by the interior walls within a dwelling unit that are perpendicular to that common wall. Since framing will usually be done before any drywall gets hung, the goal is to leave a gap between the common wall framing and the interior wall framing so that drywall can slide through that gap and be hung to create one continuous plane at the common wall. It’s not common practice, and requires coordination. Expect the first project to have challenges. Consider finishing a sample unit before the others so you can do a pre-test and correct any issues. This can also provide a mock-up for orienting all the trades that can impact the air barrier. Hope that helps!