Unvented Flat Roof Assembly

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Unvented flat roof assembly. Test roofing membranes for integrity prior to covering from below. Before constructing a flat roof assembly please refer to the unvented roof assembly comments under 6 2 vented and unvented roof assemblies and if applicable 6 3 parapet walls. Unvented roof systems and advanced framing strategies created date. Sc historically typical construction of homes in canada and the us have vented attics between the ceiling of the interior space and the roof.

Unvented flat roof assembly. Department of energy building america webinar high performance enclosure strategies. In unvented flat or low slope roofs with parapets perform a full flood test to ensure leak free installation of roofing membrane. We agree that avoiding sheathing rot is critical and that air permeable insulation such as fiberglass or cellulose cannot be used alone.

By installing spf insulation spray in place insulation in lieu of mineral fiber insulation in the joist cavity of a flat roof or between rafters of a cathedral ceiling the assembly may perform the same as or better than that of a typical. Insulating unvented roof assemblies. Additionally an unvented roof assembly is safer in areas exposed to wildfires. Joe lstiburek building science corporation subject.

In the most recent issue of fine homebuilding martin holladay wrote a piece on insulating unvented roof assemblies. Unvented metal roof assemblies are common on warehouses factories and shopping malls. Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. The most common way to eliminate venting from a roof assembly is to use a spray foam spf insulation.

This presentation was delivered at the u s. An unvented assembly can perform well but it s important to get the details right to avoid sheathing rot. Foam free don t stay stuck in the sci finightmare of foam foam foam. The colder the climate the thicker the rigid insulation required.

Unvented roof assemblies author. In high wildfire areas vented roofs are a real problem because of burning embers being pulled into the vent causing the fires to spread lstiburek says. Roof assemblies must control for exterior moisture in a monolithic and complete fashion. Condensing surface temperature controlled the thickness of the rigid insulation at both the roof deck and perimeter is determined by a calculation procedure similar to figure 5.

An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation.