Residential Building Inspector B1Roof-Ceiling ConstructionEasy
An inspector is examining the roof framing of a new single-family residence. The rafters are 2x8s spaced at 24 inches on center. The attic space is unvented and insulation is installed directly against the underside of the roof sheathing. What is the minimum required clear airspace between the insulation and the roof sheathing for this assembly?
- ANo airspace is required if the roof assembly is unvented.
- BAs per manufacturer's instructions for the insulation type.
- C1 inch (25 mm) clear airspace.
- D1/2 inch (13 mm) clear airspace.
Show answer & explanationAnswer & explanation
Correct answer: A. No airspace is required if the roof assembly is unvented.
For unvented attic assemblies, the IRC explicitly states that no air space is required between the insulation and the roof sheathing. The insulation is permitted to be in direct contact with the underside of the roof sheathing.
Why the other options are wrong
- B. While manufacturer's instructions are important, code specifies the minimum requirements for unvented assemblies.
- C. This airspace is often associated with traditional vented attics or cathedral ceilings to allow airflow.
- D. This airspace is often associated with traditional vented attics or cathedral ceilings to allow airflow.
Unvented Attic Airspace
In an unvented attic assembly, insulation can be in direct contact with the roof sheathing, as no ventilation airspace is required.
- Applies to unvented attic assemblies only.
- Contrasts with vented attics where airspace is critical.
- Eliminates the need for baffles or air chutes.
Memory trick: Vented needs space to breathe, unvented is sealed, no need to concede.