Type III construction is the type formally known as ordinary construction. It’s defined by a simple combination: noncombustible exterior walls (typically brick or concrete block) paired with wood-framed interior structures for floors, roofs, and interior walls. If you’ve walked through an older downtown district and seen brick buildings with wooden floors and roof framing visible inside, you’ve seen ordinary construction in person.
What Makes It “Ordinary”
The name stuck because this combination of masonry exteriors and wood interiors was, for a long time, the most common way to build in American cities. Brick or block walls went up on the outside, and standard wood framing filled in everything else. The International Building Code (IBC) classifies it as Type III, and the National Fire Protection Association describes it as a “mixed masonry/wood building.”
The key rule is straightforward: exterior walls must be framed with noncombustible materials or fire-retardant-treated wood, while floor and roof framing can be standard, untreated wood. The interior wood members must be smaller in dimension than what’s required for Type IV (heavy timber) construction, which uses much larger, more fire-resistant beams and columns. So ordinary construction sits in a middle ground: tougher than an all-wood building, but not as fire-resistant as concrete, steel, or heavy timber structures.
Exterior vs. Interior Requirements
The IBC draws a clear line at the exterior wall plane. Exterior wall framing and sheathing must be either noncombustible or fire-retardant-treated wood. But once you cross into the interior, the rules relax. Floor joists, rim boards, blocking, and other elements within the building can be untreated wood or any other material the code allows for interior building elements.
This distinction matters in practice. In many multi-family projects built as Type III, the exterior walls carry a 2-hour fire-resistance rating using fire-retardant-treated wood, while interior floor assemblies only need a 1-hour rating and use standard untreated lumber. The result is a building that resists fire spreading between buildings (thanks to those masonry or treated exterior walls) but relies on other protective measures to slow fire inside.
Two Sub-Types: Protected and Unprotected
Ordinary construction splits into two categories that significantly affect how the building performs in a fire.
Type III-A (protected) requires fire-resistance ratings on interior elements. Floor construction needs a 1-hour rating, and interior bearing walls need a 2-hour rating. The wood framing is still there, but it’s covered with protective layers like gypsum board that slow the spread of flames. This is the version used in most new residential and commercial projects.
Type III-B (unprotected) has the same noncombustible exterior walls but requires no fire-resistance rating on floor construction. Interior bearing walls still need 2 hours of protection, but floors and roofs are essentially exposed wood framing. You’ll find these buildings frequently in warehouse districts of older cities, where brick-walled buildings with open wood-framed interiors were standard before modern fire codes tightened requirements.
How Tall Can These Buildings Be
Because ordinary construction uses combustible wood interiors, building codes limit its height more strictly than they limit steel or concrete buildings. The exact allowances depend on what the building is used for and whether it has a sprinkler system.
For most common uses (offices, retail, residential, assembly spaces), a Type III-A building without sprinklers can reach 65 feet and 3 to 5 stories, depending on occupancy type. Add a full sprinkler system and those limits increase: up to 85 feet in height and typically one additional story. Type III-B buildings get slightly less room, topping out at 55 feet without sprinklers and 75 feet with them, with 2 to 4 stories allowed depending on use.
Residential buildings (apartments, condos) with a residential sprinkler system can go up to 4 stories in both III-A and III-B, reaching 60 feet. With a full commercial sprinkler system, Type III-A residential buildings can reach 5 stories and 85 feet.
Fire Safety Considerations
The biggest fire concern with ordinary construction is what happens behind the walls and above the ceilings. Wood-framed buildings contain concealed spaces: stud cavities, dropped ceilings, floor cavities, soffits, and attic voids. If fire enters these hidden channels, it can travel rapidly through the building without being visible until it’s well established.
Building codes address this with two strategies. Fireblocking uses materials placed inside small concealed spaces (like wall stud cavities) to prevent flame and hot gases from traveling vertically through the wall. Draftstopping works on larger concealed spaces, such as floor cavities and attics, to limit horizontal fire spread. Both are required in light-frame wood construction and are critical to making ordinary construction perform safely.
The noncombustible exterior walls do provide a meaningful advantage: they slow fire from jumping between buildings. This was the original reason cities pushed for masonry exteriors in dense urban areas, and it remains a practical benefit in tightly spaced developments.
Where Ordinary Construction Fits Among the Five Types
The IBC recognizes five construction types, numbered I through V. Type I and II use entirely noncombustible materials (steel, concrete) and are the most fire-resistant, suitable for high-rises and large institutional buildings. Type IV is heavy timber, which uses large wood members that char slowly in a fire rather than burning through quickly. Type V allows combustible materials throughout, including wood-framed exterior walls.
Type III, ordinary construction, occupies a practical middle position. The masonry or noncombustible exterior walls give it better fire separation than all-wood Type V buildings, while the wood interior framing keeps costs lower than all-steel or all-concrete construction. This balance is why it became so widespread for mid-rise apartments, mixed-use buildings, retail strips, and small commercial structures, and why it continues to be one of the most commonly specified construction types for projects in the 3-to-5-story range.