The following list of questions were taken from an intense study and crosswalk of the new 2015 Michigan Energy code. At the time of this writing, only a few of the questions have been reviewed by code officials and should not be construed as “official” interpretations from the Bureau of Construction Codes. As more questions arise and are interpreted by experts, they will be posted here.
You may want to visit the BCC site to review the Code Errors and Conflicts document.
Q: Can building cavities be used as return ducts?
A: Maybe. An interpretation by the BCC is included in the Code Conflicts and Errors (link above). However, that is only an “interpretation” and does not represent actual code. This interpretation did not go through the formal process required for writing code and should only be used as “advice” to help the local inspector make an interpretation.
Chapter 11 says NO, but the mechanical chapter says yes, as long as it can be sealed properly. When such a conflict occurs in the code book, Section R102.1 says, “…the most restrictive shall govern.” which would be the energy chapter.
What is important to know about using building cavities as a (return) duct is that it must still meet the requirements for sealing and other definitions of a duct. In addition, the building official needs to be able to inspect the duct for such sealing. The building official may also require that the duct system be tested even if all ducts are located in the building envelope.
If the duct system needs to be tested, and it fails at final, that can be a real problem. This is probably the greatest reason to AVOID USING UNDUCTED BUILDING CAVITIES. A fully ducted system with all joints sealed is far more likely to pass a duct leakage test.
Q: Can Kraft paper or cardboard be used as an air barrier?
A: No, but the code definition leaves it a little vague. The code book defines AIR BARRIER as material(s) assembled and joined together to provide a barrier to air leakage through the building envelope. From the definition of an air barrier per Joe Lstribek: “Impermeable to airflow, continuous over the enclosure, able to withstand the forces that may act upon it during and after construction, and durable over the expected lifetime of the building.”
Q: Does having an operable window in the kitchen allow me an exemption from venting the range hood to the outdoors?
A: No. Range hoods must be vented outdoors with a system capable of 100 CFM section M1503.1. Or the kitchen must have 25 CFM of continuous ventilation.
Besides the requirements, the purpose of venting the range hood is to exhaust odors, combustion byproducts, water vapor, and grease laden air OUT of the building. Opening a window does not necessarily exhaust those elements. From a safety standpoint, think about the possibility of boiling something over and really steaming or smoking up the kitchen and setting the smoke detector off. That often results in the battery being taken out of the smoke detector.
Q: Does having an operable window in the bathroom allow me an exemption from venting the bathroom?
A: No. Section M1507.4 states that bathroom exhaust be capable of 50 CFM intermittently or 20 CFM continuous. It is important to note that a fan with a rating of 50 CFM will typically only be capable of drawing 35 to 40 CFM, so you should install a minimum 75 CFM to pull 50+.
Just like the kitchen fan in the previous question, the purpose of the bath fan is to exhaust odors and water vapor from the bathroom so it does not cause mold/mildew/decay in the bathroom. Opening a window does not necessarily draw air in or out and it cannot be expected that the occupants will open a window in the bathroom during the winter or a rainstorm.
Q: Do I need to install an ERV/HRV for mechanical ventilation?
A: No. Whole house mechanical ventilation is required per section 1507.3, and there are many other options for mechanical ventilation besides heat or energy recovery ventilators. While those are both great options for a high performance home, a continuous running bath fan capable of handling the bath fan requirement and the CFM requirement of whole house mechanical ventilation is also an easy and affordable option.
Air cyclers are another option for a “supply only” strategy. These systems have a motor controlled damper and a control box which can be set to open the damper and turn on the air-handler fan to draw air into the return duct independent of the thermostat. Section N1103.5.1 requires that such a system be served by an ECM motor on the air handler fan.
Q: Does the makeup air intake with a counter-weighted “skuttle” damper count as mechanical ventilation?
A: No. Such a system does not have a controller capable of running the system to meet the demand for ventilation. Those dampers simply open when the air handler is running, typically at the demand of a thermostat. Such a damper would only count as “whole house mechanical ventilation” if the system had another control besides a typical thermostat and used an ECM blower motor.
Q: Do I need to hire a certified person or company to conduct the blower door test?
A: No. In fact, section 1126.96.36.199 doesn’t specify any requirements of the person doing the testing as long as they follow the protocol and issue a report. At the discretion of the local inspector however, you MAY be required to hire an independent third party certified person to do the testing. At this time, the two accepted certifications are BPI and RESNET.
Q: If there is a duct in the framed floor over the garage (in the bonus room) does that duct still count as being inside the thermal envelope?
A: Maybe. This is subject to interpretation and details of the construction method. If the duct is down tight to the drywall of the garage ceiling instead of being tight to the sub-floor above, then it may be considered outside the thermal envelope and would be required to be insulated to R-8 (section N1103.2.1) and would be required to be tested for leakage (section 1103.2.2). If however it is tight to the sub-floor and has R-30 insulation between the duct and the garage ceiling drywall, then it is within the thermal envelope and exempt from the testing requirement. The key word in the code passage regarding this is “entirely”. The exception reads “The total leakage test is not required for ducts and air handlers located entirely within the building thermal envelope.”
Q: Can I use REScheck to calculate Total UA or Performance compliance?
A: Yes. This is really at the discretion of local code officials however because the letter of the code appears to eliminate that option. Since the 2015 IECC is a more strict code than this Michigan Code, it should be recognized as a compliant code. Using this path however will penalize you if you have less than R-49 attic insulation and more air infiltration than 3 ACH50 which are requirements in the 2015 IECC.
Another option for these paths might be to hire a HERS Rater to help with compliance documents. There are also paths to compliance for HERS Ratings and ENERGY STAR certification which might offer some other trade-offs and benefits.
Q: Is there another software program available to help calculate compliance?
A: Yes, REM Design, from Architectural Energy Corp. might be an option; however, the software costs $500 per license and has a steep learning curve for many users. The newest version with the Michigan code should be out soon. Other programs may be available in the near future.
Q: Is rim and band joist insulation required to have an air barrier material over fiberglass or cellulose insulation?
A: Yes, but this is also subject to interpretation on a local level. Table 1188.8.131.52 specifically states that rim joists shall be insulated and “include the air barrier”. If using closed cell foam, no other barrier is typically needed if the foam is at least 2” thick, but if using open cell foam, the foam must be 5 ½” thick to be considered an air barrier. The band joist between the first and second floor also needs to be covered with an air barrier because it comprises the building envelope. Table N1184.108.40.206 specifically states that “a continuous air barrier shall be installed in the building envelope. Exterior thermal envelope contains a continuous air barrier.”
Q: If using a centrally located return register in a hallway and transom grills above bedroom doors, are those transom/transfer points required to be ducted?
A: See the first question regarding building cavities as ducts. These transfer grills are considered part of the duct system.
Q: Since insulation is required on the full height of the foundation wall (N1102.2.8) can I insulate the exterior below grade section of the wall then insulate the interior side for the above grade portion so I don’t have to protect the above grade insulation on the exterior?
A: The code only states that the full height of the wall needs to be insulated for the prescriptive path, so yes, this is allowed; however, a previous version of the code required that the overlap area between the two layers be 24″, so some inspectors may require that measure to be followed.
Q: In determining the amount of required mechanical ventilation, should we include the square footage of the basement to find the amount on table M1507.3.3(1)?
A: Yes, the first column of the table asks for the area of the “Dwelling Unit” so we must look at the code definition. In plain language, a dwelling unit is the whole house, apartment, townhouse, etc. because it has all the necessary living facilities. It makes no reference to “finished” or “habitable” space.
Q: Is ACCA Manual D, J, and S required for all systems?
A: YES. Energy code section N1103.6 Specifically states that the systems shall be sized according to Manual S based on Loads Calculated with Manual J. Section M1601.1 states that the duct systems shall be installed according to Manual D.
Q: Do the gored elbow joints of metal transition ducts need to be sealed?
A: YES. Section M1601.4.1 does not make any exceptions for such elbows. “Joints, longitudinal and transverse seams and connections shall be securely fastened AND SEALED…”
Q: When installing ductwork in an insulated enclosed crawlspace (with no vents to the outdoors), do the ducts need to be insulated or does there need to be a register supplying heat to the crawlspace in order to call it “conditioned space”?
A: NO on the insulation, YES on the register. The ducts do not need to be insulated. If you read the definition of “conditioned space” in chapter 2, it clearly states that the space can be directly or INDIRECTLY heated or cooled. With no insulation on the ducts, and no insulation on the sub-floor above, the crawlspace is being indirectly heated by the floor and the ductwork. No duct insulation is needed. HOWEVER, section 408.3 regarding enclosed crawlspace foundations DOES require that there be a supply and return air pathway in that space unless a continuous exhaust fan is installed.
Q: When building an addition which must comply with the code, how do we comply with the blower door and duct leakage requirements of the addition and not the whole house?
A: The code does not directly address this, but here are the best recommendations: First check to see if the existing house and duct system comply with the provisions for infiltration and duct leakage, you might get lucky. If the house passes BEFORE the addition, then test it again AFTER the addition is built and make sure it still passes. OR: Since most additions are built from the outside, and an entrance opening to the existing house is cut as a last step, it may be possible to blower door test the addition without testing the rest of the house. It might also be possible to construct a temporary wall to close off the addition. The duct system can also be tested before it is closed in. You might have to get creative about testing, but it can be done.
Q: My code official is requiring the garage to comply since I’m adding heat out there! Can they do that?
A: You bet they can. If the garage is going to become “conditioned space” then it must comply with the code. Check the definitions in your code book for “conditioned space”. If it is a detached structure, you may have an argument that it isn’t a dwelling unit.
Q: In a mixed use building with residential dwelling units over commercial space, how should the dividing floor be treated?
A: The book is not very clear on this, so much of the interpretation is up to the local official. What is important to understand is that the residential unit must comply with chapter 11 of the MRC without regard the unit below. In a recent project involving this scenario, the rater and the local inspector agreed to call the commercial space a “conditioned crawlspace” which gave the unit above some credit for having an insulated foundation.
Q: For slab-on-grade construction, what are the insulation requirements?
A: The prescriptive requirement for slab insulation varies by climate zone for depth, either 2ft or 4ft. All climate zones use R-10. The distance can be either vertical or horizontal or any combination of the two. The most important (and often overlooked) detail is that the vertical perimeter of the slab needs to be insulated. So if the insulation is laying horizontally under the slab, there must also be a piece which covers the vertical (4″ typically) of the slab edges. If the insulation is vertical on the inside of the frost wall, it also needs to extend up to the top of the slab edge. Typical and allowed practice is to cut a 45° bevel on the foam so the top edge is not exposed. If the slab is heated (radiant) then the prescriptive R-value is an additional R-5.