The Hot Details on Fire Resistive Construction & Other ISO Classifications

With wildfires blazing across North America, and property owners fearing for their families, homes and businesses, having the right insurance coverage before disaster strikes takes on a whole new level of importance. How fire-resistive is your property? For property managers, reinsurers and risk pools, knowing your fire-resistance class and having the right ISO classifications  data for your insurance Statement of Values becomes a key place to start.

What are ISO Classifications?

ISO Classifications are construction categories determined by the Insurance Services Office (ISO) and designed to assess the construction materials of a building to determine its level of combustion. These groupings are important for builders, appraisers and underwriters — basically, anyone who owns or deals with property — to calculate replacement costs and make sure that your building is insured for an accurate amount of coverage in the case of a risk event. They’re an important element in COPE data (that is Construction, Occupancy, Protection and Exposure information) that organizations need to collect regarding their property for insurance purposes. And it’s this information that helps determine your Commercial Property Insurance Rating, a rate group of insures with property of similar features.

A mistake in your ISO classification data can have a big effect on your coverage and potential losses due to a fire. Think of it this way: if your building is classified at the most flammable level, but it’s fire-resistive, you’re likely to be paying for more insurance than you need and, thus, higher rates. But if your building is highly-flammable yet incorrectly classified as fire-resistive… Sure, you might have lower rates but also less coverage to replace the structure if a fire does break out. Defeating the purpose of your insurance coverage. Either way, having the wrong ISO construction classification can greatly impact your bottom line.

There are two important factors that are taken into account for ISO construction classifications:

  1. The Building Elements: The materials that make up the structure itself, inside and out. So, this would include the frame, exterior and interior bearing and non-bearing walls, beams, joists and roof.
  2. The Fire-Resistance Rating: The amount of time a passive fire protection system can withstand a standard fire-resistance test. (Note: not all of the construction classifications carry fire-resistance ratings.)

To classify a building, ask yourself what materials make up the following construction elements:

  • The building frame?
  • The interior and exterior bearing walls?
  • The floor construction?
  • The roof construction

And also:

  • What is the fire rating of each of these materials?

The answers then help valuation experts classify the building into one of the six ISO classification categories:

  • Class 1: Frame
  • Class 2: Joisted Masonry
  • Class 3: Noncombustible
  • Class 4: Masonry Noncombustible
  • Class 5: Modified or Semi Fire-Resistive
  • Class 6: Fire-Resistive

Let’s talk a little bit about each one.

Class 1: Frame

This category deals with buildings where the exterior walls, floors and roofs are constructed of combustible materials — typically, wood. These buildings are classified as “Frame” even if some of the exterior walls are built with noncombustible or slow-burning materials, like stone or brick masonry veneer or metal cladding. These elements don’t change the fact that the frame itself, which supports the structure, is highly-flammable, easily damageable and can become unstable in a fire. Frames are found commonly in housing with no more than three or four stories. Because of the significant combustibility of frames, this Class has no fire-resistance rating.

Class 2: Joisted Masonry

The Joisted Masonry category includes buildings that have exterior walls of either masonry or fire-resistive construction, but also combustible floors and roofs. This masonry might be brick, reinforced or non-reinforced concrete, hollow concrete masonry, or stone. Because these materials are harder to ignite, their fire-resistance rating is listed as “not less than one hour,” meaning it takes an hour or more for the materials to potentially catch fire. Unfortunately, with combustible floors and roofs, buildings in the Joisted Masonry category are still subject to some considerable fire damage. Typically, these structures are houses, small offices, or retail buildings with no more than three or four stories.

Class 3: Noncombustible

Here, you’ll find buildings where the exterior walls, floors, roofs and supports are all made up of slow-burning and noncombustible materials. These structures are often warehouses and manufacturing facilities that commonly have steel frames combined with masonry fill, brick veneer, metal sheathing and an exterior insulation finishing system. In Noncombustible buildings with multiple stories, floors are generally constructed of concrete on a steel frame with a steel deck. This ISO Classification group has no fire-resistance rating.

Class 4: Masonry Noncombustible

Within this class are buildings in which the exterior walls are at least four inches thick (or more!) and constructed of masonry materials such as concrete block, reinforced masonry or tilt-up concrete. The floor and roof are then typically made of metal or other slow burning/noncombustible items. This offers lots of stability, handles high temperatures well and is less likely to collapse in a fire. You’ll find this class of construction in shopping centers, strip malls, office buildings, warehouses and schools. As with the Joisted Masonry class, this fire resistance rating is listed as “not less than one hour.”

Class 5: Modified or Semi Fire-Resistive

In the Modified or Semi Fire-Resistive class, we categorize buildings with exterior walls, floors and roofs made up of masonry materials four inches thick or greater. Here, the exterior load bearing walls are constructed of masonry or non-combustible materials while the exterior nonbearing walls and panels can be slow-burning, combustible or with no fire resistance rating at all—hence the “Semi Fire Resistant.” The “Modified” refers to the protection techniques that are sometimes applied to the structured steel in these buildings. These could be coatings of sprayed concrete, plaster or mastics. Buildings in this class are typically high-rise and mid-rise office buildings or condominiums. In a Modified or Semi Fire-Resistive building, the Fire-Resistance Rating is “less than two hours, but greater than one.”

Class 6: Fire-Resistive

This ISO classification group involves buildings with walls of solid masonry, including reinforced concrete less than four inches thick or hollow masonry less than eight inches thick. Exterior bearing walls should be made of noncombustible materials, but exterior nonbearing walls can be of combustible materials. Fire-Resistive buildings are usually high-rise office buildings, condos or parking garages. Their fire-resistance rating is two hours or more.

But What if There are Multiple ISO Construction Classes in One Structure?

It’s worth noting that if you have two different ISO Classes of materials within one building, and the lower fire rating comprises of over a third of the building, you should use the lower fire rating for the whole building. And if there are three or more different ISO types, use the most prominent ISO Classification for the structure.

A building is only as strong as its most vulnerable structural element. So that’s why knowing your ISO Construction Class can be critical to ensure you get the right insurance coverage and mitigate risk – in wildfire season or any season.

Want to see how Centurisk’s AMP Property Risk Management software can help keep you prepared for tomorrow’s big risk challenges? Simply fill out the form below and a member of our team will be in touch!

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