Interpretation #9545

Original Request

Code Version: 2023
Code: RESIDENT
Code Description
Chapter: 8
Section: R806.5
Topic: Unvented attic and unvented enclosed rafter assemblies

Question

Is it the intent of Section R806.5 of the Florida Building Code – Residential that once an attic is constructed as an unvented attic with air-impermeable insulation applied directly to the underside of the roof deck and the space is fully brought inside the building thermal envelope, that dedicated supply and return air ducts are not required to be installed in the attic?

Answer Published 06/12/2026 at 1:13 PM

No. R806.5 does not require a dedicated supply and return air conditioning duct in an "unvented attic space" inside the thermal envelope. These cooling ducts are optional and up to the designer. However, this space is required to be tested for air leakage per R402.4.1.2 testing where it states under #7 that If an attic is both air sealed and insulated at the roof deck, interior access doors and hatches between the conditioned space volume and the attic shall be opened during the test and the volume of the attic shall be added to the conditioned space volume for purposes of reporting an infiltration volume and calculating the air leakage of the home since that space is now within the thermal envelope. Further, this space no longer falls under the definition of "attic" in the energy conservation volume. For the roof to be considered insulated, roof insulation shall be at least the R-value required to meet Section R405.2.1. Some designers provide conditioning to this space to reduce humidity which can occur, but this is optional.

Commentary

None.