---
title: "Understanding Floor-Ceiling Assemblies and Fire Ratings"
url: https://stacklist.com/card/9331b200-2044-4deb-95a6-600ab77cd194
published: 2026-10-09T14:42:47.154Z
stack: https://stacklist.com/stack/d2ee3c27-eae3-4a1e-aee2-633850a041f1
summary: "Fire-resistance ratings come from complete floor-ceiling assemblies, not individual materials like gypsum underlayment. Treadstone gypsum underlayment appears in over 110 UL designs and contributes to verified fire-resistance ratings when used as part of a tested system."
tags: "gypsum-underlayment, fire-ratings, floor-ceiling-assemblies, ul-design, fire-resistance, construction-materials, building-codes"
key_entities: "Treadstone (technology), gypsum underlayment (technology), UL (organization), fire-resistance rating (concept), floor-ceiling assembly (concept), FR25 (concept), FR30 (concept)"
classification: "reference"
content_hash: "sha256:cd0f072164a8c7e662173cd147764487806f45d7e6692125099c937df250ef32"
acp_version: "0.2"
token_counts_approximate: 468
visibility: public
agent_accessible: true
status: "final"
---

# Understanding Floor-Ceiling Assemblies and Fire Ratings

## Is Gypsum Underlayment Fireproof?

![Gypsum underlayment](https://formulatedmaterials.com/wp-content/uploads/2026/07/gypsum-fireproofed-1024x512.png)

Fire-resistance ratings don't come from a single material. They come from how materials work together as a system. When you have a tested floor-ceiling assembly, every part contributes: the membrane above, the structural framing, the base layer below, the topping poured on top, and any acoustic dampening. Swap out even one component and you've moved outside what's been tested and verified.

This means a gypsum underlayment doesn't carry its own fire rating in isolation. What exists is a one-hour or two-hour rated floor-ceiling assembly, each identified by its specific UL design number. That design encompasses the entire stack: the membrane, the subfloor, the gypsum pour at the right depth, and everything else in the configuration. When engineers and spec writers do their job right, they call out the UL design by number, not the underlayment product alone. Manufacturers earn their place by getting listed in the designs their customers need.

## How Treadstone Sits in This Picture

Treadstone makes fire-resistive gypsum underlayment in FR25 and FR30 grades, where FR stands for fire-rated. The product line appears in over 110 UL fire-resistance designs. That number matters on project submittals because it proves the gypsum pour is part of a system that carries a verified rating.

By itself, Treadstone doesn't make a floor fireproof. No gypsum underlayment does. What it does is add non-combustible substance and thermal buffering to a complete assembly that, taken as a whole, achieves a fire-resistance rating. On any project requiring a one-hour or two-hour rated floor, the real questions become: which UL design is the assembly built to, and is the specified underlayment listed in that design?