Interview with Craig Drumheller: Insights to Buried Ducts in Attics

The 2018 edition of the International Energy Conservation Code (IECC) has been published, and it includes new provisions regarding HVAC ducts buried in vented attic insulation. The code changes, proposed by Craig Drumheller from the National Association of Home Builders (NAHB), allow ducts to be buried in attic insulation, and when using the performance path, provides credit for the improved duct efficiency.    

We sat down with Craig to dive into some of the details of his proposed code change, and how it can influence duct system design and energy savings.

  1. Can you give us a brief explanation of your history and current role at NAHB?
    For 14 years, I was a senior energy research engineer at the Home Innovation Research Labs, for the last 5 years I have been the Director of Construction Codes and Standards at the National Association of Home Builders, specializing in energy, green building, plumbing and mechanical codes.

  2. Can you explain your proposed code change for buried ducts in attic insulation?
    There were three components of the buried duct code changes approved in the 2018 IECC:

    • First was to explicitly allow ducts to be buried in attic insulation with additional requirements in hot-humid climate zones to reduce condensation potential.
    • Second was to have an effective duct R-value for ducts buried under sufficient insulation to prevent condensation from forming on or around the duct.
    • Third, create specific criteria for duct tightness and attic insulation levels in order for ducts to be considered in conditioned space.

  3. You were the one who proposed changing the code. What were the origins for this code change, and why did you pursue it?
    Buried ducts have never been specifically disallowed in the code, however, many jurisdictions have decided to require ducts to be elevated above the attic insulation because of concerns about displaced insulation and the potential for condensation on the ducts. Based on research I had previously done, other research I had read, and personal experience with jurisdictions, I felt that prohibiting buried ducts was creating a missed opportunity for energy savings by disallowing an energy saving technique. When discussing this subject with some of the NAHB builder members who had similar experience, there was a strong interest in pursuing these code changes.

  4. When will it go into effect?
    These code changes have been incorporated in the 2018 International Energy Conservation Code. This edition of the code was published in September 2017, however, at this point the latest edition of the IECC has yet to be adopted. If your jurisdiction is working on a previous edition of the IECC, you may be able to convince your jurisdiction to include these changes, building departments are typically amenable to allowing changes that are available in a newer published edition.

  5. Achieving the appropriate R-value with your change is key. Is there any training that goes into code changes like this one to ensure that implementation/installations are sufficient to achieve the desired results?
    A significant amount of research has been conducted by a number of organizations showing the equivalent performance as long as the code required level of insulation is achieved.

    A number of research papers and a tech note are available to better illustrate the new code requirements. The Home Innovation Tech Spec does a good job simplifying the new code language and showing illustrations of the new provisions.

  6. Is this code a requirement (all buried ducts in must be insulated), or merely a requirement if you choose to insulate them (all insulated buried ducts must meet this R-value)?
    The new code language is strictly an option. If a builder chooses to bury their ductwork, they must comply with the requirements. According to the IECC, ducts in the attic already require R-8 insulation. R-13 duct insulation will be necessary for buried ducts in climate zones 1A, 2A and 3A.

  7. How much energy can people expect to save when they bury their ducts in attic insulation?
    Estimates range from 2 to 10% of total household energy use. So there is a significant energy saving opportunity at a potentially low cost.

  8. Is this a requirement across the country, or is it limited to certain regions?
    Nowhere is this a requirement, and it is universally applicable for ducts in ventilated attics. Some of the requirements will vary based on climate zone. And, of course, the new changes apply to jurisdiction which have adopted the 2018 IECC. Also, the state of California has allowed buried ducts in their Title 24 energy code for a number of years.

  9. Where can people go to find more information about this?
    A large amount of research has been done by Home Innovation Research Labs and Steven Winters and Associates. Most of this research was done for the Department of Energy. You can locate the 2018 IECC code itself here.

Craig’s contributions to the 2018 IECC were just one of a number of proposed changes to the code. If you would like more information regarding building code evolutions and compliance, you may find our recent webinar, Know the Code: Understanding Building Code Compliance, highly useful. In this webinar, John Elverum from Johns Manville and Eric Makela from Cadmus, discuss the trends that drive code changes, what you can expect to see in coming years, and the latest changes in the codes pertaining to HVAC and mechanical insulation.

For more details about the 2018 IECC, please click here.