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Home / Assemblies / UL D125
UL D1251-hr Fire RatingFloor/CeilingLoad-BearingSTC 41
Steel JoistFiberglass BattDesign

Steel Joist Floor/Ceiling — single layer 5/8" Type C gypsum board

UL-listed 1-hour fire-rated steel joist floor/ceiling assembly. C-channel steel joists at 16" o.c. with R-19 fiberglass batt, single layer of 5/8" Type C gypsum board ceiling.

Cross-Section Diagram

12345FLOOR/CEILING ASSEMBLYSECTION · NOT TO SCALE5 LAYERSsee legend for ① ② ③
Legend
1Floor covering(varies)
23" concrete on steel deck(3")
3C-channel steel joists at 16" o.c.(10.0")
4R-19 fiberglass batt
55/8" Type C gypsum board(5/8")

Specifications

Fire Rating
1-Hour
STC Rating
STC 41
Load Bearing
Yes
Total Thickness
12.12"
Source / Publisher
UL (Underwriters Laboratories)
Design Number
D125
Assembly Type
Floor/Ceiling
Test Standard
CAN/ULC-S101
Construction Group
Non-Combustible
Number of Layers
5 layers

Applicable Codes

IRC R302.1IBC 2024 Table 722.1NFPA 5000

Construction Summary

C-channel steel joists at 16" o.c. with R-19 fiberglass batt, single layer of 5/8" Type C gypsum board ceiling

Material Layers

LayerMaterialThickness
1Floor coveringvaries
23" concrete on steel deck3"
3C-channel steel joists at 16" o.c.10.0"
4R-19 fiberglass batt—
55/8" Type C gypsum board5/8"

Important Notice

This assembly listing is for reference only. Always verify against the current UL Product iQ database before specifying in construction documents. Material substitutions may void the fire rating. Consult with a qualified fire protection engineer for project-specific requirements.