Unvented Cold Deck Flat Roof

One of the best ways to insulate a roof whether sloped or flat is to install rigid foam on top of the roof sheathing.

Unvented cold deck flat roof.

Exterior foam can reduce air leaks limit condensation at the sheathing layer interrupt thermal bridging through the rafters and make ice dams unlikely. 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. The colder the climate the thicker the rigid insulation required. However in many situations the insulation may need to be primarily or entirely below the flat roof membrane and between the roof joists if so what are the best options.

The higher the interior moisture level the thicker the rigid insulation required. There is no need for additional ventilation. It is universally recommended that cold deck flat roof construction should be avoided. Unvented flat roofs a technical discussion flat roofs have often been built with the insulation all on top of the vapor closed drainage plane as this avoids dew point condensation issues inboard of the roofing.

Unvented flat roof assembly. In unvented roof assemblies the thermal moisture and air control boundaries are moved to the roof deck so that the attic space is at the same condition as the living space and air movement between the two does not contribute to energy waste occupant discomfort or contaminant problems.