Roof-Ceiling Construction

Roof Drainage

Minimum roof slope 1/4:12 and drainage system requirement.

Identification and Grade (Roof Framing)

Roof framing lumber must be graded and marked — minimum No. 2 grade.

Roof Trusses

Section R802.10 — Roof Trusses. Roof trusses shall be designed, manufactured, and installed in accordance with ANSI/TPI 1 and accepted engineering practice. Truss design drawings shall be prepared by a registered...

Ceiling Joist and Rafter Framing

Section R802.1.1 — Ceiling Joist and Rafter Framing. Ceiling joists and rafters shall be designed in accordance with the span tables in this section or engineered per accepted practice. Members shall be supported laterally to prevent...

Ceiling Joist Spans

Provides allowable ceiling joist spans for common lumber species and grades based on joist spacing, dead load, and live load conditions.

Rafter Spans

Provides allowable rafter spans for common lumber species and grades based on rafter spacing, dead load, live load (20 psf ground snow load), and roof slope.

Roof Sheathing

Parent section for all roof sheathing requirements including lumber sheathing and wood structural panels.

Lumber Sheathing

SPAN RATING SHEATHING - Establishes allowable spans for lumber roof sheathing per Table R803.1.

Wood Structural Panel Sheathing

Requirements for wood structural panels used as roof sheathing.

Identification and Grade

Wood structural panels must have grade marks or approved certification.

Allowable Spans

MINIMUM ROOF SHEATHING THICKNESS - Specifies minimum thickness based on rafter/truss spacing.

Installation

Installation requirements for wood structural panel roof sheathing. Max 9" cantilever at gable ends.

Roof Ventilation

Attic ventilation required: 1/150 of attic area, or 1/300 if 40-50% is upper ventilation. Unvented attic assemblies allowed under specific conditions.

Ventilation Required

ATTIC VENTILATION: Minimum 1/150 ratio (reduces to 1/300 with balanced vents or vapor retarder). MUST maintain 1" clearance at eaves for airflow. Use baffles to keep insulation from blocking soffit vents. 50/50 split between intake (soffit) and exhaust (ridge) is ideal. Do NOT mix power vents with ridge vents.

Minimum Vent Area

Section R806.2 — Minimum Vent Area. The minimum net free ventilating area shall be 1/150 of the area of the vented space. The minimum net free area may be reduced to 1/300 of the vented space provided that a Class I ...

Attic Access

Section R807.1 — Attic Access. Buildings with combustible ceiling or roof construction shall have an attic access opening to attic areas that exceed 30 inches in height over an area of 30 square feet or greater....