Educational Summary: "Understanding Unvented Attic and Enclosed Rafter Assemblies: Code 1203.3 Florida Edition

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Educational Summary: "Understanding Unvented Attic and Enclosed Rafter Assemblies: Code 1203.3"​

Code 1203.3 focuses on the regulations for unvented attic spaces and unvented enclosed roof framing assemblies. These assemblies are typically formed when ceilings are directly attached to the roof framing members and the structural roof sheathing. To be compliant with the code, several conditions must be met:

1. Thermal Envelope Inclusion: The unvented attic space must be entirely within the building's thermal envelope.
2. Vapor Retarder Restrictions: No Class I vapor retarders are allowed on the ceiling side of these assemblies.
3. Shingle/Shake Installation: For wood shingles or shakes, a minimum 1/4-inch vented airspace is required between them and the roofing underlayment over the structural sheathing.
4. Insulation in Cold Climates: In colder climate zones (5-8), any air-impermeable insulation used must either be a Class II vapor retarder or have a Class II vapor retarder coating.
5. Insulation Compliance: Insulation must comply with specific requirements:
   • Air-Impermeable Insulation: It must be applied directly under the roof sheathing.
   • Air-Permeable Insulation: This must be installed in accordance with additional guidelines, including specific R-values for condensation control.
   • Combination of Insulations: A combination of air-impermeable and air-permeable insulations must also meet specific requirements.
   • Temperature Maintenance: An alternative method involves maintaining the monthly average temperature of the roof sheathing above 45°F.
6. Special Provisions for Warm Climates (Zones 1-3): Specific requirements are outlined for air-permeable insulation in these zones, including the installation of a vapor diffusion port, port area specifications, and vapor permeance ratings.
7. Air Supply for Insulation: The air must be supplied either from ductwork or a supply fan, with specific flow rate requirements.

Exceptions: The code does not apply to structures like swimming pool enclosures, data centers, hospitals, or art galleries. It also excludes enclosures in climate zones 5-8 that are humidified beyond 35% during the coldest months.

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This section of the code is essential for ensuring the safety and efficiency of unvented attic and roof framing assemblies, especially in terms of thermal management and moisture control. The title "Understanding Unvented Attic and Enclosed Rafter Assemblies: Code 1203.3" reflects the content's focus on providing clear guidelines for these specific architectural elements.

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