This sloped roof assembly consists of roof joist framing with exterior sheathing at the top side and the ceiling finish below. A service cavity can be constructed on the interior between the ceiling finish and sheathing/polyethylene to allow for running of electrical, plumbing, and HVAC services without penetrating the ceiling air barrier. Penetrations in the air barrier are sealed at the interior side of sheathing/polyethylene. High effective R-values are achieved by installing insulation in the joist space.

The depth of the insulation is limited by the depth of the roof joists, with allowance for ventilation. Engineered trusses can be used to create a deep joist space. Continuity of the air barrier and allowance for adequate ventilation at the top side of the insulation are critical to the performance of this assembly.