New ORNL Roof Design
eyremountllc
| Posted in Energy Efficiency and Durability on
Stumbled upon this new roof design by ORNL, what do you all think
http://www.rdmag.com/News/Feeds/2012/09/energy-ornl-roof-and-attic-design-proves-efficient-in-sum/
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Roger, I couldn't get that link to work, but I did find the original paper at the Oak Ridge website [DOC]
A Prototype Roof Deck Designed to Self-Regulate Deck Temperature and Reduce Heat Transfer.
info.ornl.gov/sites/publications/files/Pub30786.docx.
The best drawing of the design is included in the press release about it. http://www.ornl.gov/info/press_releases/get_press_release.cfm?ReleaseNumber=mr20120910-00.
This is particularly interesting to me because of retrofits I want to do on a couple of houses.
Thank you so much for posting that.
Is this a design that would be worth considering for a new near passive house or is it more beneficial for retrofits?
Elizabeth,
The payback period for these details is very long, as ORNL researchers admit. It only makes sense in hot climates with high air conditioning bills -- and probably only for homes with attic ductwork (something you will never find in a Passivhaus).
My advice remains unchanged: if you pay attention to air sealing the attic floor, and if you keep all ductwork and HVAC equipment within the home's conditioned space, and if you have at least code-mandated levels of insulation on your attic floor -- then it hardly matters what your attic temperature is.
Lucy,
I agree. This is particularly exciting for retrofit projects.
Elizabeth and Martin,
I agree. Definitely retrofit. No one with the right mind should be putting HVAC ducts in the attic in a new construction, also, why would anyone not seal the attic floor! The study concludes, "The most cost-effective retrofits for an attic are repairing the leaks through the attic floor and in the HVAC ducts".
Martin,
I find it interesting that "In Baltimore the payback is estimated at 11 years for the insulated and ventilated roof deck as compared to a 68 year payback for sealing the attic with open cell spray foam."
I wonder though if the outcome would be different if instead of using open cell spray foam to seal and insulate, tape the attic with an air-sealing tape from either the ProClima or the Siga family and then use batt/cellulose to insulate.