Understanding Michigan's Five Types of Building Construction

Understanding Michigan’s Five Types of Building Construction: Fire Resistance and Material Classifications

In the State of Michigan, every building is classified into one of five construction types, as defined in the Michigan Building Code (adapted from the International Building Code – IBC). These classifications are critical for determining how buildings are constructed and how well they resist fire. They also influence the permitted height, area, and occupancy type of the structure.

This article explores the five types of construction used in Michigan, focusing on the combustibility of materials and the fire-resistance ratings of key structural elements, such as the frame, floor, roof, and walls.

🔥 Why Construction Type Matters

The primary purpose of construction classification is life safety—to slow down or contain the spread of fire long enough to allow occupants to escape and firefighters to respond. Buildings must be able to resist fire for specific durations, typically between 1 to 3 hours, depending on their use and size.

Each type of construction has subcategories (A and B), where:

Type A means “protected” construction (fire-resistant materials are used to protect structural members),
Type B means “unprotected” construction (less or no fire-resistive protection is provided).

🏗️ Michigan’s Five Types of Construction

Type I – Fire-Resistive Construction

Combustibility: Noncombustible
Materials: Reinforced concrete, protected steel
Fire Resistance:
- Structural frame: 2–3 hours
- Floor construction: 2–3 hours
- Roof construction: 1.5–2 hours

Description: Type I construction offers the highest level of fire resistance. All building elements (load-bearing walls, floors, roofs, columns, and beams) are noncombustible and fire-rated. Commonly used for high-rise buildings, hospitals, and large commercial buildings.

Type II – Noncombustible Construction

Combustibility: Noncombustible
Materials: Steel, concrete (less fireproofing than Type I)
Fire Resistance:
- Structural frame: 0–1 hour
- Floor/Roof: 0–1 hour

Description: While made of noncombustible materials, Type II construction has lower fire-resistance requirements than Type I. Often found in newer commercial buildings and warehouses with steel framing.

Type III – Ordinary Construction

Combustibility: Mixed (noncombustible exterior walls, combustible interior)
Materials: Masonry (exterior), wood (interior)
Fire Resistance:
- Exterior walls: 2 hours
- Interior structural elements: 0–1 hour

Description: Type III buildings have noncombustible exterior walls (usually brick or concrete block), but the interior structure (floors, roofs, framing) may be wood. Common in older urban buildings and multifamily residential structures.

Type IV – Heavy Timber (HT) Construction

Combustibility: Combustible (but with inherent fire resistance)
Materials: Large-dimension solid or laminated wood
Fire Resistance:
- Heavy timber members are not rated by hours but must meet dimensional standards (e.g., minimum 6×10″ beams)

Description: Type IV uses large-dimension timbers that char on the surface when exposed to fire, which slows fire progression and maintains structural integrity. Common in mill buildings, warehouses, and now, modern “mass timber” structures using CLT (Cross-Laminated Timber).

Type V – Wood Frame Construction

Combustibility: Combustible
Materials: Wood or other approved combustible materials
Fire Resistance:
- Structural frame, floor, and roof: 0–1 hour

Description: The most combustible and least fire-resistant type, Type V includes single-family homes and small apartment buildings. All major building elements may be made of wood. It’s cost-effective but requires strict fire separation and fire-stopping measures.

🧱 Fire-Resistance Ratings: What They Mean

Fire-resistance ratings are based on standard tests that measure how long a component can resist exposure to fire while maintaining its structural integrity and insulation properties. For example:

1-Hour Rated Wall: Can withstand fire exposure for one hour before failing.
3-Hour Rated Column: Maintains its load-bearing capacity for three hours in fire conditions.

These ratings are achieved by using:

Fire-resistive materials (e.g., gypsum, concrete, intumescent coatings)
Fireproof assemblies (e.g., layered drywall on framing)
Encapsulation of combustible materials

🧯 Implications for Builders and Designers in Michigan

Knowing the building’s construction type helps determine:

Allowable building height and area
Egress and exit requirements
Fire protection systems (sprinklers, alarms)
Insurance costs and building codes compliance

Early decisions on construction type influence the design, material selection, and cost. Michigan code officials will evaluate these classifications when reviewing building permits.

Summary Table: Michigan Construction Types

Type	Combustibility	Common Materials	Typical Uses	Fire Resistance (hours)
I-A/I-B	Noncombustible	Reinforced concrete, protected steel	High-rises, hospitals	2–3 hrs
II-A/II-B	Noncombustible	Steel, concrete	Warehouses, schools	0–1 hr
III-A/III-B	Mixed	Masonry exterior, wood interior	Apartments, commercial	0–2 hrs
IV (HT)	Combustible	Heavy timber, glulam	Old mills, modern mass timber	Meets size specs
V-A/V-B	Combustible	Wood frame	Homes, small buildings	0–1 hr

Final Thoughts

Understanding Michigan’s five construction types is fundamental for builders, designers, code officials, and owners alike. Fire safety begins with choosing the right materials and ensuring that fire-resistance ratings are met. These classifications are more than just regulatory checkboxes—they’re a vital part of ensuring buildings are safe, resilient, and code-compliant.