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Cool Roof

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    Harry Whitver

    1. Insulate the Underside

    Insulate and air-seal the underside of the roof deck using a flash-and-batt or full-cavity spray-foam treatment, creating an unvented attic that can reasonably house HVAC equipment and sealed and insulated duct runs in a semi-conditioned space to reduce leakage and thermal loss.
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    Harry Whitver

    2. Protect the Deck

    A peel-and-stick or mechanically fastened roll-out membrane serves as a weather and incidental water barrier and a secondary air barrier for the deck. While not primarily related to keeping the deck cool, the membrane beads and sheds water to keep the deck dry, thus mitigating potential moisture damage.
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    Harry Whitver

    3. Apply Battens

    Ventilated battens fastened to and held slightly off the deck by small “pucks” enable air to flow from the ventilated end caps at the eaves to a ventilated ridge and vice-versa, keeping the deck cool and dry. Above-deck eave and ridge ventilation is essential. Without one or the other, there’s no way to facilitate flow.
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    Harry Whitver

    4. Fasten the Finish

    The battens also serve as nailers for the roof finish, and the airflow will also help keep the underside of the tiles or panels dry and cool. The system works with mechanically fastened roofing finishes (except asphalt comp) and those set in mortar, though care should be taken to make sure excess mortar does not hinder ventilation.

Heat island effect is one of those green building terms that is coming late to the residential realm but can be a significant part of the energy-efficient equation. Well known in commercial circles, it refers to the roof’s propensity to be a heat sink (or island) that enables thermal transfer to undermine energy-efficient investments elsewhere in the building. Non-res folks often solve this issue with white or light-colored roofing membranes that effectively reflect the sun’s heat away from the surface. For sloped-roof housing using almost anything but an asphalt comp, the solution is a ventilated roof assembly that holds the roofing material slightly above the deck to facilitate air transfer under the tiles or panels, which mitigates overheating the attic and living spaces below to keep cooling-energy consumption in check. The roofing material can also help. Like membranes, lighter claddings will reflect rather than absorb solar heat gain.