IECC and Multi-Family Buildings

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Up and down the front range of Colorado we are seeing more and more code jurisdictions adopt either the 2012 or 2015 IECC.  From a building science perspective, this is a step forward toward better performing buildings because these two codes require mandatory air leakage targets be met by all segments of residential construction three stories or less.  What I mean by this is that the code understands the importance of gaining control and predictability of the air flowing through our buildings.  I like to say that air is a freight train and like a train it carries cargo from point A to point B. The cargo it carries is heat/energy, moisture, and pollutants. The issue is that air does not always carry its cargo in a straight line on tracks from inside a house directly outside the house and deposit its load into the ambient air. A properly ducted fan may take air and its cargo to the outdoors, but often air takes its cargo into building assemblies and deposits it there, causing long-term building durability and efficiency issues for our homes. The code now recognizes that tight homes increase durability and efficiency and now understand that visual inspection itself cannot ensure house tightness.  The fundamental change in the code from the 2009 IECC to the 2012 or 2015 IECC is this recognition and the move from a choice to administer a blower door test or visually inspect to a mandate that you visually inspect and test to ensure tightness of the homes we build.

EnergyLogic tests homes and has been helping builders use the Simulated Performance pathway through code since the 2006 IECC.  Unlike other pathways in the energy code, the flexibility gained in the performance path allows for the most cost-effective means to develop the energy specifications for a house because we can trade off house tightness for R-values and U-values in the thermal envelope. This means that we understand that there is absolutely no problem achieving the code required 3 air changes per house at 50 Pascals (3 ACH50) in a single-family home.  In fact, the 2012 and 2015 IECC offer a checklist for how to be successful in the mandatory air barrier and insulation table R402.1.1.  We also know with certainty that it is not easy for multi-family buildings to achieve this same air leakage target. Currently, code does not recognize the difficulty of achieving 3 ACH50 in multi-family homes and buildings.  The City of Denver has accepted EnergyLogic’s code amendment to allow multi-family homes and buildings to have a leakage rate of 4ACH50. The city of Fort Collins allows a CFM/sqft of shell area measurement to be used to express air leakage in multi-family project.  So far they are the only jurisdictions in the state that I am aware of that have amended this section of the code to better reflect the realities of creating airtight multi-family buildings. On a national level, EnergyLogic has submitted a code change proposal for the 2018 IECC that makes a clear distinction between single-family detached homes and multi-family attached homes with achievable air leakage targets for both. We will have to wait until October to see if the proposal is accepted.

So where does that leave our multi-family builders?

Whether you are building duplexes, townhouses, or stacked multi-family buildings, house tightness is solely dependent on attention to detail with regard to air sealing adiabatic common fire rated walls, floors, and ceilings.  We recommend beginning by removing all draft-stopping materials (rock wool and fiberglass that are air permeable) in these fire rated assemblies and replacing them with solid fireblocking materials that actually stop the movement of air. By doing this you now have reasonable-sized holes that, depending on the jurisdiction, the assembly, and the skill level of the air sealing contractor, can be sealed. Next, you must treat common walls, floors, and ceilings as you would treat assemblies that separate conditioned space from the outdoors. The codes air barrier and insulation mandatory table/checklist must be applied to these common fire rated assemblies. For example, if there is a tub or shower pan, drop ceiling, or knee wall adjacent to an adiabatic common fire rated wall, floor, or ceiling, an air barrier needs to be installed.  Lastly, these details cannot be an afterthought!  They need to be addressed from the first design charrette, through a trade partner kickoff meeting, to mid-phase air barrier and insulation rough quality assurance inspection, if there is to be any hope of achieving 3 ACH50 when the home is blower door tested at a final inspection.  Blower door testing occurs when the home is complete and when it is impossible to achieve significant air sealing objectives at this point of construction.  Small changes in the tightness of the home may be able to be achieved, but air takes the path of least resistance; so if you have not blocked and sealed it out behind the drywall it is unlikely that you will be able to do more that achieve a small increase in the tightness of home at a final stage of construction.  In other words, the work has been done at the time of the rough inspection and the evaluation of the work is done at the final inspection.

In conclusion, get involved and take full advantage of EnergyLogic’s third-party inspection and testing services.  Get us involved as early as possible in the design of your multi-family project, and let us train all your trade partners at a kickoff meeting, how to successfully work toward meeting the requirements of code.  It is not easy, but attention to detail, quality assurance inspection, and greater understanding by the trade base will make 3 ACH50 achievable.

 

Robby Schwarz

 

Who to Contact:
Robby Schwarz
Principal, Director of Builder Relations

Email Robby
720-838-0677

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