ICM in construction stands for “incombustible materials,” a classification you’ll typically encounter in property records, real estate listings, or insurance documents. It indicates a building whose structural components are made from materials that do not burn, such as concrete, steel, masonry, and glass. In building code terms, ICM construction aligns with Type I and Type II classifications, which require non-combustible structural elements but differ in how much fire resistance those elements provide.
What Non-Combustible Means in Practice
A material qualifies as non-combustible when it passes standardized fire testing (ASTM E136 or ASTM E2652). Some materials, like concrete, masonry, glass, and steel, are considered inherently non-combustible and don’t need to be tested at all. When a building carries an ICM designation, its primary structural elements, including walls, floors, roof assemblies, and the structural frame, are built from these materials rather than wood or other combustible options.
This doesn’t mean the building contains zero combustible material. Interior finishes, furniture, and some non-structural components can still be combustible. The classification focuses on the structural skeleton of the building and whether fire can compromise its integrity.
How ICM Relates to Building Code Types
The five standard construction types (Type I through Type V) form a spectrum from most to least fire resistant. ICM construction falls within the first two categories, both of which require non-combustible structural materials. The key difference between them is how long those materials can withstand fire before failing.
Type I (Fire Resistive, Non-Combustible) is the most robust. It comes in two subtypes. Type I-A requires exterior walls and the structural frame to resist fire for 3 hours, floor and ceiling assemblies for 2 hours, and roof protection for 1.5 hours. Type I-B drops those ratings slightly, with 2-hour protection for exterior walls and the structural frame and 1-hour protection for the roof assembly. Type I-A is commonly found in high-rise buildings and institutional occupancies like hospitals. Type I-B is typical of mid-rise office buildings and residential buildings.
Type II (Non-Combustible) still uses non-combustible materials but with lower fire-resistance ratings. Type II-A (protected non-combustible) requires 1-hour fire resistance across exterior walls, the structural frame, and floor, ceiling, and roof assemblies. You’ll see this in newer school buildings. Type II-B (unprotected non-combustible) is the most common non-combustible construction for commercial buildings. The materials themselves won’t burn, but they have no added fire-resistance rating, meaning steel beams, for example, aren’t coated with fireproofing.
For comparison, Types III through V progressively allow more wood and combustible materials. Type III permits wood for interior structural elements. Type IV uses heavy timber or cross-laminated timber for floors, roofs, and interior framing. Type V allows wood or other approved materials throughout, which is why it includes most single-family homes.
Why the Classification Matters for Property Owners
If you’re seeing ICM on an insurance document, it directly affects your premiums. Non-combustible buildings carry lower fire risk, which generally translates to lower insurance costs compared to wood-frame (Type V) or mixed construction (Type III) buildings. Insurers use construction type as one of the primary factors in calculating property risk.
For real estate transactions, the construction type tells you something about the building’s durability and maintenance profile. Concrete and steel structures typically have longer lifespans than wood-frame buildings, tolerate moisture better, and are less susceptible to termite damage. They also tend to perform better in natural disasters like hurricanes and wildfires.
The tradeoff is cost. Non-combustible construction is significantly more expensive to build than wood framing, which is why it’s concentrated in commercial, institutional, and multi-story residential buildings where codes require it rather than in low-rise housing where codes allow lighter construction.
Where ICM Buildings Are Most Common
Building codes mandate non-combustible construction based on a building’s use and size. The taller and more densely occupied a building is, the stricter the requirements. High-rises almost universally require Type I construction. Hospitals, nursing homes, prisons, and other facilities where occupants can’t easily evacuate also require high fire-resistance ratings.
Beyond code requirements, non-combustible construction is standard in aerospace facilities, pharmaceutical manufacturing, data centers, airport terminals, mining and mineral processing plants, food and beverage production facilities, and energy infrastructure. These buildings combine large footprints, high-value contents, and operational environments where fire resistance is a practical necessity rather than just a code checkbox.
Unprotected vs. Protected Non-Combustible
One detail worth understanding is the distinction between protected and unprotected non-combustible construction, because both fall under the ICM umbrella but behave very differently in a fire. Unprotected steel, for instance, won’t catch fire, but it loses structural strength rapidly at high temperatures. A steel beam can begin to fail at around 1,000°F, which a building fire can reach within minutes.
Protected non-combustible construction addresses this by adding fireproofing to structural steel, typically spray-applied coatings or encasement in concrete. This buys time, anywhere from 1 to 3 hours depending on the rating, for occupants to evacuate and firefighters to respond before the structure is at risk of collapse. If your property record specifies “protected” or lists a fire-resistance rating alongside the ICM designation, that tells you the building has this added layer of safety.