Mid-Rise Multifamily Wood Construction: Type V Wood Frame and Type IIIB Hybrid for 5-6 Story Apartments

Mid-rise multifamily wood construction includes Type V wood frame (5 stories typical maximum) and Type IIIB hybrid (6 stories with concrete podium under wood frame). Substantial portion of multifamily market — economical for 4-6 story apartments substantially competing with mid-rise concrete and steel. Code-compliant per IBC. Substantial knowledge required for fire protection, structural, and assembly details. Understanding code requirements helps GCs deliver successful mid-rise wood projects.

This post covers mid-rise multifamily wood construction.

Type V Wood Frame

Type V wood frame:

Type V wood frame construction. Wood frame entire building (no other structural materials primary). Up to 5 stories typically per IBC with allowed building height/area. Specific fire protection required including sprinklers, fire-rated assemblies. Sprinklers throughout per IBC requirements. Substantial cost-effective vs concrete or steel for mid-rise multifamily. Substantial multifamily use — dominant 4-5 story format in many markets. Specific to IBC requirements.

Type IIIB Hybrid (5-Over-1)

5-over-1 substantial:

5-over-1 (Type IIIB hybrid) substantial multifamily format. Concrete or masonry podium (Type IA construction) at base — typically commercial/parking ground floor. Wood frame above (Type V) for residential floors. Total 6 stories typical (5 wood + 1 podium). Substantial multifamily format particularly urban infill. Substantial cost-effective vs full concrete or steel. Specific code provisions allowing combination. Substantial popularity in last decade.

Fire Protection

Fire protection substantial:

Fire protection substantial in wood mid-rise. Sprinklers throughout per NFPA 13R typical for residential. Fire-rated assemblies 1-hour typical between units, corridors. Fire blocking and draft stopping in wood frame preventing fire spread in concealed spaces. Fire-rated separations between dwelling units, between residential and other uses. Stair and exit protection enabling safe egress. Specific code substantial throughout.

Structural Considerations

Structural specific:

Structural considerations specific to wood mid-rise. Wood frame typical dimensional lumber for walls, floors. Engineered wood (LVL, LSL, glulam) for substantial spans, beams. Cumulative shrinkage substantial across multiple stories — wood shrinks across grain producing 1+ inches across 5 stories. Lateral systems (shear walls) for wind, seismic. Specific to seismic zones (substantial requirements high seismic). Specific span limitations affecting layouts.

Acoustic Performance

Acoustic substantial multifamily:

Acoustic performance substantial in multifamily. STC (Sound Transmission Class) 50+ between units per code (substantial floors and walls). IIC (Impact Insulation Class) 50+ between floors preventing footstep noise. Specific assemblies meeting requirements through gypsum, insulation, resilient channels. Substantial detailing throughout. Resilient channels typical for substantial floor performance. Specific to code minimums but quality projects exceed. Substantial for tenant satisfaction particularly upper floors.

Energy Code

Energy code requirements:

Energy code requirements specific. IECC (International Energy Conservation Code) compliance required. Substantial insulation requirements including walls, roofs, floors. Air sealing important reducing infiltration. HVAC efficiency standards. Substantial fenestration ratings (windows, doors). Specific to climate zone with varying requirements.

Bottom Line

Mid-rise multifamily wood construction includes Type V wood frame (5 stories) and Type IIIB hybrid (6 stories with podium). Type V wood frame substantial multifamily use. 5-over-1 substantial format urban infill. Fire protection substantial including sprinklers, rated assemblies. Structural considerations including engineered wood, shrinkage, lateral. Acoustic performance substantial multifamily concern. Energy code compliance required. For GCs serving multifamily, mid-rise wood substantial market. Quality construction supports substantial multifamily delivery cost-effectively.