Roof-Ceiling Construction
Roof framing, ceiling construction, and structural requirements
Sections
Roof Drainage
ROOF DRAINAGE - Must prevent water accumulation. Gutters/downspouts sized per ASPE/SMACNA.
Roof Drainage - Maryland
Roof drainage must discharge 6+ ft from foundation. Maryland stormwater rules may require rain gardens/infiltration in some counties.
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
Parent section for ventilation requirements.
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.
Attic Ventilation Requirements - Maryland
Attic ventilation: 1/150 ratio (can reduce to 1/300 with vapor retarder). Critical for Maryland humidity control.
Minimum Vent Area
MINIMUM VENT AREA - 1/150 ratio required, or 1/300 with 40-50% upper ventilation.
Unvented Attic Assemblies - Maryland
Unvented attics allowed with air-impermeable insulation (spray foam). Thermal barrier required where spray foam is exposed.