Construction types I–V: non-combustible to combustible

One-line orientation

Construction types I–V (IBC Chapter 6) rank a building’s fire resistance from fully non-combustible (I) to combustible wood frame (V) — and the type, paired with occupancy, sets the allowable height and area.

Key points

• Type I — highest fire resistance: most elements (walls, columns, beams, floors) non- combustible — concrete and steel. High-rises, hospitals, skyscrapers.
• Type II — non-combustible, lower ratings: also non-combustible materials but generally lower fire-resistance ratings than Type I. Factories, warehouses where cost matters but non-combustible is still required.
• Type III — non-combustible exterior, combustible interior: exterior walls must be non- combustible to limit fire spread; interior elements may be wood. Common in dense urban / older cities.
• Type IV — Heavy Timber: large-dimension wood beams and columns meeting minimum sizes; resists fire because the large timber chars predictably, insulating the core. Exposed-wood buildings, barns, churches.
• Type V — combustible: allows the most wood/combustible material; lowest fire resistance. Typical residential wood-frame construction.

Construction types I–V — ranked by fire resistance

Higher numeral means more combustible and less fire-resistant — not “better”.

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Key

• non-combustible (concrete / steel)
• heavy timber — chars, self-insulates
• combustible light wood frame

A building's construction type, paired with its occupancy, sets the allowable height and area. Two traps: Type III is non-combustible exterior-only, and Type IV heavy timber resists fire by charring, unlike light-frame Type V.

Confusions / comparison

Type	Fire resistance	Materials	Note
I	Highest	Non-combustible (concrete/steel)	High-rises, hospitals
II	Lower than I	Non-combustible, lower ratings	Factories, warehouses
III	Mixed	Non-combustible exterior, combustible interior	Urban street walls
IV	Good (by mass/char)	Heavy timber	Large members char predictably
V	Lowest	Combustible (wood frame)	Houses, small apartments

Related

→ A vs B subtypes (this module): the protected/unprotected split within each type · Occupancy groups overview (this module): occupancy + construction type set height/area · F / S / H / U (this module): combustibility logic recurs here.