Identify and indicate on the floor plans and sections the exterior boundary (EB) of the building.

The exterior boundary is the surface that separates indoor air from outdoor air. The EB normally occurs at the same place as the thermal insulation. For example, outside walls make up a large portion of the EB.

To carry out this step, mark the EB on a set of working drawings with a highlighter-type marker. Indicate the elements of the house that divide inside from outside. Once these are highlighted, you can see at a glance where the air barrier probably needs to be -- the inside surface of the EB.

On the plans and sections, circle leakage sites where sealing will be needed to make the air barrier continuous. Most of these sites fall into one of two categories:

• joints in sheet materials, such as where panels of subfloor meet or where drywall meets the subfloor.
• places where interior walls intersect the EB. These leakage sites are your air sealing targets.

Plan view - lower level

Plan view - upper level

As you think about each leakage site, you may find it helpful to refer to the detail drawings in Air Sealing Details.

Indicating the location of the EB may seem to be a waste of time. However, experience has shown that builders and designers may be unclear about whether a particular wall, or part of a wall, is an “inside wall” or an “outside wall.” Deciding between the two is a critical step for homes with more than one floor level -- two story homes, homes with basements, split levels, etc. In these cases, it is common to forget where the outside is in relation to the inside. For example, you might have to stop and think about areas such as stairways, common walls, chaseways for ducts and pipes, overhangs and cantilevers. Walls, ceilings and floors that separate garages and living spaces are often overlooked. Air sealing will be more successful if you identify -- early as possible -- the areas that need to be sealed.

Some details may require special attention. Soffits, dropped ceilings, utility chases and furred spaces raise questions. Should the air barrier go inside the volume created or should it be carried out around the outside? Stairways and bathtubs are troublesome spots because they often adjoin other walls and components.