Party Walls

Here’s a question our clients often ask: “I’m building a new residential building, should I use LEED for New Construction (NC) or LEED for Multifamily Midrise?” The answer isn’t exactly simple, especially with the introduction of new credit requirements in LEED v4 and the fact that USGBC allows project teams to choose between the two rating systems. Ultimately, it’s often a difficult decision based on the goals and final design of the project. So, in an effort to help clear up the confusion and possibly make the decision a little easier for you, we decided to break down a few scenarios that highlight key differences between the rating systems that may not be apparent upon first glance. In this first installment, we’ll start with a smaller multifamily building to get a sense of the essential differences between the rating systems and begin to understand the critical decision-making points.

Our example today is a four-story, wood-framed multifamily building with no ground floor retail. Four stories is the minimum eligible height for residential projects to use either Midrise or NC, as residential buildings under four stories must use the LEED for Homes rating system.

Four stories is also about as tall as building codes will typically allow for a wood-frame building. Additionally, many residential buildings of this size will include individual HVAC systems for each unit rather than a central chiller or boiler. Believe it or not, the building materials and systems installed make a big difference when determining which rating system is best for your building. So, the height and framing materials of your building are main factors that can help make this decision for you.

Since our example building in this scenario is wood-framed and has individual rooftop condenser units with furnaces located in mechanical closets, we would advise this project to utilize the LEED for Multifamily Midrise rating system. The Multifamily Midrise system was written with this exact type of project in mind: it focuses on residential building strategies and systems rather than fitting residential buildings into a system designed for larger commercial-style construction. Let’s take a closer look at a couple of LEED credits from both rating systems:

• First, we’ll examine the Minimum Energy Performance prerequisite for both Midrise and NC. One of the first differences you’ll notice is that Midrise combines the energy modeling and commissioning requirements into this prerequisite, whereas NC keeps them separate. You’ll also notice that the commissioning requirements for Midrise include prescriptive requirements for HVAC system (duct) leakage and construction document sheets that include unit sealing, air barriers, and compartmentalization. The NC Commissioning prerequisite is less prescriptive with its requirements for these systems.
  • It is especially important to note this difference, as the Midrise certification model also requires on-site verification for duct leakage and unit compartmentalization. Duct leakage is a major energy waster, and the Department of Energy estimates that it can cost a homeowner or tenant hundreds of dollars per year. By verifying that the units in the project are not only properly designed, but also properly installed, the Midrise rating system goes a bit further than NC in ensuring that in-unit energy use will actually be reduced.
• Next, let’s take a look at the Indoor Environmental Quality prerequisites for ventilation. LEED NC requirements necessitate that a building meet ASHRAE 62.1-2010 ventilation rates for all common areas and unit spaces; whereas in Midrise, unit spaces are required to comply with ASHRAE 62.2-2010, which is a residential ventilation standard. Not surprisingly, we have found that the requirements for ASHRAE 62.2-2010 are more appropriate in residential buildings than the 62.1-2010 requirements, which focus primarily on commercial construction.
• Additionally, the Midrise rating system includes specific requirements for kitchen and bathroom ventilation, two particularly important areas in a residential setting where moisture build-up can lead to mold growth and particulate matter can lead to other negative health effects.
• When looking at the EQ credit category, you’ll notice that the Midrise system includes several prerequisites not included in the commercial rating system, such as Compartmentalization. We already mentioned Compartmentalization while discussing Minimum Energy Performance, but it’s worth noting that compartmentalizing each unit is critical in multifamily buildings, as it’s what helps keep air from leaking between units. Do you want to help heat or cool your neighbor’s unit with leaks from your own? Do you want to inhale smoke that has seeped in from the unit next door? I know I don’t. The NC rating system doesn’t place as much emphasis on the verification of compartmentalization as does Midrise, and for these reasons, we believe Midrise is a better fit for these types of projects.

Hopefully these examples help identify a few of the key differences between the NC and Midrise rating systems. If you have a project that falls in the gray area between these rating systems, get in touch! Our expertise continues to lead the industry as we help builders and developers make the best choices for sustainable, energy-efficient buildings.

In our next installment, we’ll take a look at a 10-story building with ground floor retail, as there are other necessary considerations for these types of projects.

By Sean Fish, Senior Sustainability Consultant