New Roof-Attic Design Improves Efficiency

The media relations group for Oak Ridge National Laboratory just released more information about recent field tests by ORNL of a new roof and attic system that keeps homes cool in the summer and prevents heat loss in the winter.  The system is explained in the graphic embedded above (click to expand).  In addition, I’ve included some graphics below to illustrate more of what the system looks like and how it saves energy.

The system employs a passive ventilation strategy that is expected to cost about $2,000 for a retrofit situation with savings of roughly $100 per year, yielding a payback of about 20 years.

Foil covered polystyrene insulation (with the ventilation gap) is installed over and between rafters for new construction or on top of an existing shingle system in a retrofit.  With the new roof assembly, air moves from the underbelly of the attic into an inclined air space above the roof, according to an ORNL statement, so that “heat that would have gone into the house is carried up and out,” said Bill Miller of ORNL’s Building Envelope Group.

In the summer, the temperature of the attic is reduced as a result of the roof detailing and, according to observations by ORNL, the thermal load of the home is thereby reduced. Further, ORNL found improved efficiencies even if the attic floor is insufficiently insulated.

The research and findings are discussed in more detail in a paper, “Prototype Roof Deck Designed to Self-Regulate Deck Temperature and Reduce Heat Transfer,” published by the National Roofing Contractors Association.  A PowerPoint of the background research can be found here [PDF].

[+] More about this roof-attic system tested by Oak Ridge National Laboratory.

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  • caveman664

    Did they indicate what the costs would be on a new construction?

  • caveman664

    Did they indicate what the costs would be on a new construction?

    • Preston

      I’m still digesting all the material from the Word version of the report, but I think there’s some helpful case study information in here for you:

      • Phillip Norman Attic Access

        Here is the cited Word document as pdf, edited with the parent ORNL URL.
        I am grateful for discovery through this blog, and want to be part of the conversation. One flaw I see is reliance on continuous roof peak venting, Such venting is wildly over-rated in some (or all?) products. I hold to a literal definition of net free area, and would penalize for friction, where length/diameter is about fifty. I understand nfa for a screen. I do not, for HPDE extrusions, alleging that stated ratings are high by at last times-three. On my house, moss would cover passages in a few years. My solution for a hot attic is one or more solar fans, served by a sheltered window or two, open and screened in summer. I can prove to purists demanding even inlet distribution in soffits, that is not necessary.

        This release is glib about how air gets into the attic, in addition to optimism about continuous roof peak venting.

        I am impressed by this video, critical of static venting.

        • Preston


        • Steven Leighton

          About the video– what temperature was the smoke at? I too am a little cautious about this proposed roof ventilation. A PV powered extractor fan or two would work wonders. The roof in the video has electrical wiring circa 1940’s! Knob and post I think it was called.

  • eeLsirhC

    This very similar to standard residential construction in Japan where the full envelope is ventilated. Glad to see someone implement it.

  • Austin Gerber

    FYI, I just read an editorial in Tauton’s Fine Homebuilding Magazine which stated a user of foil faced insulation on his home lost all cell phone reception inside. The author went on to state that Verizon has had many complaints from people who live in newer homes with same construction methods. Something to consider when building, include a cell phone signal booster into the overall budget.

  • Richard Hawkinson

    Ive been looking for a system with batt insulation up tight to the bottom of the trusses, the issues I have had are the ventilation air gap between the top of the insulation and bottom of roof sheathing and how to get a continuous vapor barrier around the wood truss webbing, any ideas out there.

  • dbull

    How does this compare to metal roofing? Sounds decent. Phillip, I love solar attic fans. Especially when they are connected to one of those controllers that cycle in house power when the sun goes down and monitors temperature.

  • Jerry

    So you couldn’t do a vaulted ceiling with this obviously? That’s what I thought it was at first. But you would have vents in the ceiling then.

  • Jerry

    So you couldn’t do a vaulted ceiling with this obviously? That’s what I thought it was at first. But you would have vents in the ceiling then.

  • Josh

    This idea is not unlike installing radiant barrier in a retrofit application – which makes me wonder why an article posted on JG regarding energy scams included radiant barrier. Some companies will try to scam people any chance they get, but there is proven science behind the use of radiant barriers to decrease heat load on a house (attic is first line of defense) and ORNL has data to back it up. That’s probably why they advocate this because of the similarities. Some companies are far from legitimate and ruin it for the rest of us who have integrity.

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