For Architects & Engineers
Fire Resistance Calculator
Precast concrete carries its fire rating in the material itself. Enter a thickness and aggregate type to estimate the fire endurance, or work backward from the rating your project requires.
Verify every rating before you specify or build
This tool is a preliminary design aid, not a code compliance document. All fire ratings must be verified by the engineer or architect of record and accepted by the authority having jurisdiction. Confirm results against the current building code, the governing PCI and ACI standards, and the producer's tested assemblies. Ratings here address the ASTM E119 heat-transmission end point only. Structural fire endurance, connections, joints, penetrations, and assembly details require separate analysis.
Solid wall panels and slabs
For single-mixture precast panels and slabs, fire endurance is governed by thickness and aggregate type. Enter what you know and the calculator fills in the rest.
Ribbed and corrugated panels
Heat transmission through a ribbed panel is governed by the thin section, the equivalent thickness, or a blend of the two, depending on how far apart the ribs sit. Equivalent thickness is the net cross-sectional area divided by the width. Ignore any part of a rib projecting beyond twice the minimum thickness.
Columns
Reinforced concrete columns need a minimum dimension for each rating. Cover to the main longitudinal reinforcement must be at least 1 in. per hour of required fire resistance, or 2 in., whichever is less.
| Aggregate | 1 hr | 1½ hr | 2 hr | 3 hr | 4 hr | Min. cover |
|---|---|---|---|---|---|---|
| Siliceous | 8 | 9 | 10 | 12 | 14 | 1 in./hr, 2 in. max |
| Carbonate | 8 | 9 | 10 | 11 | 12 | 1 in./hr, 2 in. max |
| Sand-lightweight | 8 | 8.5 | 9 | 10.5 | 12 | 1 in./hr, 2 in. max |
The reference tables
Every number this calculator returns comes from these published tables. Check your work against them.
| Aggregate | 1 hr | 1½ hr | 2 hr | 3 hr | 4 hr |
|---|---|---|---|---|---|
| Siliceous | 3.5 | 4.3 | 5.0 | 6.2 | 7.0 |
| Carbonate | 3.2 | 4.0 | 4.6 | 5.7 | 6.6 |
| Sand-lightweight | 2.7 | 3.3 | 3.8 | 4.6 | 5.4 |
| Lightweight | 2.5 | 3.1 | 3.6 | 4.4 | 5.1 |
| Aggregate | 2 hr | 3 hr |
|---|---|---|
| Sand-lightweight | 2.5 | 3.6 |
| Carbonate | 2.8 | 4.0 |
| Siliceous | 2.9 | 4.2 |
| Inside wythe | Insulation | Outside wythe | Fire endurance |
|---|---|---|---|
| 1½ in. Sil | 1 in. CP | 1½ in. Sil | 1:23 |
| 1½ in. Carb | 1 in. CP | 1½ in. Carb | 1:23 |
| 1½ in. SLW | 1 in. CP | 1½ in. SLW | 1:45 |
| 2 in. Sil | 1 in. CP | 2 in. Sil | 1:50 |
| 2 in. Carb | 1 in. CP | 2 in. Carb | 2:00 |
| 2 in. SLW | 1 in. CP | 2 in. SLW | 2:32 |
| 3 in. Sil | 1 in. CP | 3 in. Sil | 3:07 |
| 1½ in. Sil | ¾ in. GFB | 1½ in. Sil | 1:39 |
| 2 in. Sil | ¾ in. GFB | 2 in. Sil | 2:07 |
| 2 in. SLW | ¾ in. GFB | 2 in. SLW | 2:52 |
| 2 in. Sil | ¾ in. GFB | 3 in. SLW | 3:10 |
| 1½ in. Sil | 1½ in. GFB | 1½ in. Sil | 2:35 |
| 2 in. Sil | 1½ in. GFB | 2 in. Sil | 3:08 |
| 2 in. SLW | 1½ in. GFB | 2 in. SLW | 4:00 |
Sil = siliceous · Carb = carbonate · SLW = sand-lightweight (115 pcf max) · CP = cellular plastic · GFB = glass fiber board
Sources and further reading
- PCI DN-31, Fire Resistance of Architectural Precast Concrete Envelopes (Tables 1, 3, 4, and 5)
- PCI MNL-124, Design for Fire Resistance of Precast/Prestressed Concrete, 3rd edition
- PCI ASCENT, Spring 2012, Fire Design
- ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials
- IBC Section 722, Calculated fire resistance
PCI guides and manuals · PCI bookstore
Need this checked on a real project?
Our producer members and their engineers work fire ratings every day. Ask early, while panel thickness and finishes are still moving.