IBC Table 602 sets the fire-resistance rating required for exterior walls based on three variables: the building’s occupancy group, its construction type, and the fire separation distance between the wall and the nearest lot line, street centerline, or imaginary line between buildings on the same lot. Ratings range from three hours at the tightest separations down to zero hours once the wall sits 30 feet or more from the reference line. Pull the wrong number and a plan reviewer will catch it before permits issue, or an inspector will catch it after framing is up.
The Three Inputs the Table Needs
Table 602 reads like a lookup grid. You need all three inputs before it returns a number.
Occupancy group. Chapter 3 of the IBC sorts buildings by what happens inside them: Assembly (A), Business (B), Educational (E), Factory (F), High Hazard (H), Institutional (I), Mercantile (M), Residential (R), Storage (S), and Utility (U). Table 602 collapses these into three columns. Group H sits alone with the strictest ratings. Groups F-1, M, and S-1 share a middle column. Everything else (A, B, E, F-2, I, R, S-2, and U) shares the column with the lowest requirements.
Construction type. Chapter 6 divides buildings into Types I through V, primarily by whether the structural frame, floors, and walls use noncombustible materials. Types I and II require noncombustible elements like steel and concrete. Type V allows any materials the code permits, including conventional wood framing.
Fire separation distance. The distance measured at a right angle from the face of the exterior wall to the closest interior lot line, the centerline of a street or public way, or an imaginary line between two buildings on the same lot.
How to Measure Fire Separation Distance
The measurement is perpendicular to the wall face, not along the ground or at an angle, and it runs to one of three reference points. Each one has a wrinkle worth knowing.
For streets and alleys, the reference point is the centerline, not the far curb or opposite property line. A building facing a 60-foot road picks up 30 feet of separation distance before you measure anything on the far side. That alone often eliminates the need for any fire-resistance rating on the street-facing wall. The code extends the same logic to alleys and other public ways on the theory that those spaces are unlikely to be built on later.
For two buildings on the same parcel, the reference is an imaginary line between them, and the line does not have to sit equidistant between the two structures. A designer can place it closer to the better-protected building, which reduces the rating required on the other building’s wall. The catch is that shifting the line in one direction raises the requirement on the opposite building, so it’s a trade rather than a free move.
Because the measurement is perpendicular to the wall face, a wall running parallel to the lot line takes the full brunt of the requirement, while a wall at a right angle to the lot line has effectively no fire separation distance concern for that face. On tight urban lots, rotating a building even slightly can change which walls need rated assemblies.
What the Table Requires at Each Distance
At less than five feet of fire separation distance, construction type stops mattering. Every building faces the same ratings: three hours for Group H, two hours for F-1, M, and S-1, and one hour for the remaining column. The exposure risk is high enough at that range that the code gives every building the same treatment.
At 30 feet or more, the required rating drops to zero hours across the board, regardless of occupancy or construction type. The gap between buildings is large enough that the code treats the wall as having no meaningful exposure.
Between those bookends, the ratings graduate based on both distance and construction type. Noncombustible types (IA and IB) generally maintain higher ratings over greater distances than combustible types. The three-column occupancy pattern holds at every distance tier: Group H highest, the F-1/M/S-1 column in the middle, the A/B/E/F-2/I/R/S-2/U column lowest.
Load-Bearing Walls Must Also Satisfy Table 601
This is where projects get tripped up. Exterior bearing walls answer to both Table 601 and Table 602, and the higher rating wins. Table 601 assigns ratings based purely on construction type, with no regard for how far the wall sits from a lot line. Table 602 cares only about fire separation distance and occupancy. A load-bearing exterior wall must meet whichever table demands more.
Table 601 requires a three-hour rating for exterior bearing walls in Type IA construction and a two-hour rating in Type IB. Even if Table 602 would let that wall off at one hour because the separation distance is generous, the bearing wall still needs to hit the Table 601 number. Running the other direction: a Type IIB bearing wall carries a zero-hour requirement from Table 601 but can need a one- or two-hour rating from Table 602 if it sits close to a lot line.
Non-bearing exterior walls answer only to Table 602. They also benefit from a footnote the code uses to tie the wall rating to the opening rules, which can drop the requirement to zero hours entirely.
Fire Exposure Testing Direction
The rating itself comes from standardized furnace testing, and the side of the wall exposed to the furnace matters. The IBC draws a line at 10 feet. Walls with more than 10 feet of separation only need to be rated for fire exposure from the interior side, on the assumption that an exterior fire is unlikely at that range. Walls with 10 feet or less must be rated for fire exposure from both sides, because a fire in an adjacent building could hit the exterior face while an interior fire could hit the other.
Many common wall assemblies are not symmetrical. The interior face may carry layers of gypsum board while the exterior has only sheathing and cladding. An assembly that passes a one-hour test with fire on the interior side can fail the same test with fire on the exterior. On tight separation distances, you either choose a symmetrical assembly or verify that your assembly has been tested from both directions.
When the Rating Drops to Zero
Table 602 includes a footnote that routinely eliminates the need for rated sheathing on non-bearing walls. Where Table 705.8 permits a non-bearing exterior wall to have unlimited unprotected openings, the fire-resistance rating for that wall is zero hours. In practical terms, non-bearing walls on sprinklered buildings often reach this point at 20 feet of fire separation distance; non-sprinklered buildings reach it at 30 feet.
Only NFPA 13 sprinkler systems trigger the sprinklered opening allowances. NFPA 13R systems common in mid-rise residential, and NFPA 13D systems in single-family homes, do not qualify, even though they provide real fire suppression. Group H occupancies are also excluded from the sprinklered opening allowances; H-1, H-2, and H-3 buildings are directed to Section 415.6 for special requirements.
Sprinklers cannot override Table 601. A load-bearing exterior wall in Type IA construction still needs its three-hour rating regardless of sprinkler status. The sprinkler trade-off works only on the Table 602 side, which makes it most valuable for non-bearing walls and lighter construction types where Table 601 demands are already low.
What the Rating Pulls In With It
A Table 602 rating isn’t the end of the exterior wall analysis. Several other code provisions key off the number you pulled from the table.
Openings are governed separately by Table 705.8, which limits the percentage of wall area that can be windows and doors based on fire separation distance, sprinkler status, and whether the openings are protected. At less than three feet of separation, openings are prohibited entirely.
Parapets must carry the same fire-resistance rating as the wall below them when the code requires one, with a minimum height of 30 inches above the roof. Several exceptions apply, including walls that don’t need a rating in the first place, buildings with 1,000 square feet or less per floor, and roofs that are noncombustible or two-hour rated.
Projections like eaves, cornices, and balconies have their own setback rules based on fire separation distance, and combustible projections within five feet of the reference line must be at least one-hour rated construction, heavy timber, or fire-retardant-treated wood.
Penetrations and joints through rated walls must be sealed with listed firestop systems tested to maintain the wall’s rating. For walls with 10 feet or less of separation, joint systems must be tested from both sides, matching the wall assembly rule.
What Happens If the Rating Is Wrong
A Table 602 mismatch can stall a project at several points. Plan reviewers catch mismatches before permits issue, which means redesign at the drawing stage. Field inspectors catch assembly errors during framing and sheathing inspections, which means tear-out during construction. If noncompliance surfaces after occupancy, the consequences escalate to denied certificates of occupancy, mandatory retrofits, and potential liability if a fire occurs and the wall fails to contain it as the code intended.
The obligation does not end at move-in. Rated assemblies must be maintained for the life of the structure. Renovations that remove gypsum board, alter stud spacing, or add unprotected penetrations can void the wall’s rating without anyone noticing until the next inspection or the next fire. In fire-damage litigation, liability often turns on whether the structure met its Table 602 rating at the time of the incident.