By Grey Lee
LEED for Homes Certification has two paths: Low-rise and Mid-rise. In addition to having some different 'optional point' credits, the two certification paths have some key differences in Prerequisites (the pass/fail items). One of these differences, which I will discuss in this post, is EQp12.1 – Compartmentalization of Units.
Compartmentalization is an air sealing practice that focuses on limiting air movement between dwelling units within a building. Historically, the exterior boundary has been the primary plane for reduction in building air leakage. More recently, air leakage across unit boundaries has been targeted for more than energy savings. Where air can travel, sounds, smells, heat, cold and rodents can as well. The goal of the compartmentalization requirement in LEED for Homes Mid-rise is to reduce the movement of all these things. Many of us have probably experienced an apartment where neighbors share more than just the common stairwell.
Figure 1 demonstrates the intent of compartmentalization. Solid lines in this image represent walls that have been sealed to act as continuous air barriers and dotted lines indicate walls that have not been sealed. The floor plan to the left represents a building in which only the exterior boundary has been sealed while the floor plan to the right represents a building that has been compartmentalized, or sealed to prevent air movement between units.
Now, you may be thinking, how hard can it be? The entire unit gets gypsum on the walls and with the ceiling, windows and doors being sealed, where can the air come from? Well, let me tell you something: air can be sneaky!
It finds its way anywhere that it can – whether through a light fixture, electrical outlet, duct chase or behind baseboard. If you don't seal it, it will come, and meeting the LEED for Homes Mid-rise prerequisite doesn't happen by accident.
Figure 2 is a cross-section of a multifamily building in which we are looking at one unit which is bounded on all sides by other units. The orange dotted line represents the interior gypsum on the walls, ceiling, and the floor. The red arrows indicate the paths for air leakage, which can be found coming through electrical penetrations such as wall outlets and ceiling fixtures. It can also enter the unit through penetrations made by ductwork and unsealed framing in spaces between unit ceilings and subfloors above.
In my experience, residential units that have not had a compartmentalization goal are typically measured at twice or more the allowable leakage level for LEED for Homes Mid-rise. Working with a LEED Green Rater from framing, insulation, finish, and focusing on compartmentalization has shown to be an effective way to help projects meet their air leakage requirements.