The Durability Challenge of Energy Retrofits

Stan Gatland

Stan Gatland

As a member of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE),  I participate in technical committees that deal with building performance from a heat, air, and moisture perspective. One committee explores best practices for building envelope design. The committee focuses on how to manage heat, air, and moisture flow through assemblies. 

At a recent forum, members discussed concern that in the rush to create air-tight building envelopes with high levels of energy efficiency, the long-term impact on durability due to these changes may be overlooked.  Energy efficient, air-tight buildings have a greater potential to accumulate moisture and have less energy to dry out.

The Department of Energy is poised to support the energy efficiency retrofit of existing homes by improving air tightness and adding thermal insulation.  This time, hopefully, the history of the 1980s and 1990s does will not repeat itself regarding the durability issues related to energy efficiency retrofits.  Moisture related damage typically takes seven to 10 years after the retrofit of an existing home or construction of a new energy efficient home if measures are not taken to address moisture.

DOE recognizes the need to control interior humidity levels, as well as address combustion safety.  If adjustments are not made to control humidity levels and circulate fresh air it could cause other problems like excess moisture which could result in mold.

Another concern is combustion safety. By making an assembly more air-tight, you have less air available for combustion events. For example, hot water heaters and furnaces that once relied on a building’s air leakage to supply enough air to the combustion process may backdraft if enough air is not available in a well sealed home.   Direct ventilation may now be required to compensate for the retrofit.   

DOE is recommending that energy retrofit contractors address moisture management issues and combustion safety by following guidelines outlined in ASHRAE Standard 62.2 as a way to insure proper indoor air quality for residential buildings and increase the durability of assemblies.

Americans have traditionally had access to inexpensive energy but that is changing. We do need to address retrofitting older buildings, but it is crucial to not create other problems while doing so.

Stan Gatland is Manager, Building Science Technologies for CertainTeed Corporation


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  2. Stan — it’s great to see this kind of thinking. In the late 70’s, my parents built an efficient addition onto their old Maine farmhouse — passive solar, double-glazed windows (cutting edge, then), 2×6 walls … and a polyethylene vapor barrier. The builder had never seen such a thing, and put it on the wrong side of the insulation — fortunately the architect was there at the right time and caught the error before it was too late.

    It is essential that our building inspection and code process not only creates requirements for efficiency, but also for health, durability and safety. I think this will be especially challenging for retrofits. My 1920’s era house is now close to being tight enough after our energy audit identified the major leaks, but a house not designed for ventilation could end up with moisture trouble.

    All this said, I wish this were a huge problem today — it’s not because so few people know or understand the need for energy efficient houses. I am working for now, and we’re doing our best to provide quality, accurate information to readers and guidance for pros who want to get into the business.


  3. Sounds like you are off to a good start. Many people are not aware of the ramifications of adding insulation and implementing air tightness measures into existing homes. I also recommend that you consult with a home energy rater to measure the air tightness of your home and check for air pressure problems that might cause back drafting or comfort issues. Good luck with your remodeling.

  4. Thank you for pointing out the risks! I am a homeowner with an energy retrofit on my hand for a 100+ year old building. Fortunately, it is easy these days to get educated on how to go about it. One of the first things I came across in my research was the importance of moisture management – and that is true for any building, efficient or not. The other thing I learned, like you pointed out, is that an airtight, efficient building envelop must go hand in hand with a good ventilation strategy. Most modern combustion equipment is directly vented these days, which helps a lot. And the ERV and HRV technologies help owners like me to assure sufficient air exchange for (hopefully) excellent IAQ.

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