What is the Thermal Envelope?

The thermal envelope is the portion of a home that contains conditioned air. In most homes, the uppermost portion of the thermal envelope will be the attic floor. The exception is where the attic is not ventilated and the attic ceiling and walls are insulated.

Thermal Envelope Concerns

  • Insulation type (if known);
  • Insulation depth (SOP item);
  • Vapor barrier installed under insulation;
  • Radiant barrier installed (correctly);
    • Radiant barriers must be installed in a manner that allows air to flow along the underside of the roof sheathing. Failure to ventilate the sheathing may result in shortened shingle lifespan.
    • Radiant barrier sheathing (RBS) is roof sheathing with foil bonded to the underside. (Possible fire hazard: see the article on Roof Sheathing).
  • Ignition barrier where sprayed foam is used to insulate the roof.
  • Sheathing decay where sprayed foam is used to insulate the roof.

Sprayed  Foam Insulation

Sprayed foam insulation installed against the underside of the roof sheathing typically means that the attic is configured as conditioned space. Foam may hide roof leaks, allowing the structural integrity of the roof sheathing to become severely compromised from advanced wood decay before the leak is discovered. For safety reasons, inspectors should bear this in mind when walking roofs with deteriorated roof-covering materials and attics insulated with sprayed foam.