Firestop Putty Pads: Requirements and Installation
How to seal electrical boxes in fire-rated walls to maintain hourly fire ratings and STC sound ratings
Last updated: April 3, 2026
Overview
Putty pads are intumescent pads that seal around electrical boxes in fire-rated walls. Every electrical outlet, switch, and junction box that penetrates a fire-rated wall creates a weak point. The thin steel box and the gaps around it let fire, smoke, and sound pass through. A putty pad restores the hourly fire rating and the STC (Sound Transmission Class) rating of the wall assembly.
The concept is simple: wrap the back and sides of the electrical box with a soft, moldable pad that expands in a fire to seal the opening. But skipping putty pads is one of the most common fire code violations on commercial and multi-family jobs. Inspectors look for them, and missing pads mean failed inspections and rework.
This guide covers when putty pads are required by code, how they work, how to install them correctly, and what inspectors flag during walkthroughs. For a broader overview of firestop products and when to use each type, see the Firestop Product Selection Guide.
When Are Putty Pads Required?
The International Building Code (IBC) requires firestop protection for penetrations through fire-rated assemblies. Electrical boxes are one of the most common penetrations, and putty pads are the standard solution. Here is when you need them:
- Any electrical box in a fire-rated wall assembly (1-hour, 2-hour, etc.)
- STC-rated assemblies where sound transmission matters (hotels, condos, hospitals, schools)
- Listed assemblies that specify putty pads in the UL design
- Back-to-back electrical boxes in fire-rated walls (code also requires minimum separation between boxes)
Putty pads are not required on standard non-rated interior walls in single-family residential construction. If the wall has no fire rating or STC requirement on the drawings, you do not need them.
Tip: If the wall section on the drawings shows an hourly fire rating or STC requirement, every box in that wall needs a putty pad. Check the partition schedule and UL design numbers early so you can order enough pads before rough-in.
How Putty Pads Work
Putty pads use intumescent technology. At room temperature, the pad is soft and moldable, similar to modeling clay. You press it around the electrical box and it stays in place without curing or hardening.
In a fire, the intumescent material activates. It expands (intumesces) to many times its original volume, sealing the opening around and behind the electrical box. This blocks flame, hot gases, and smoke from passing through the wall assembly. The expansion happens at temperatures well below the point where fire would breach the wall, so the seal forms before the fire gets through.
At normal temperatures, the putty pad serves a second purpose: it blocks sound transmission and air leakage through the electrical box opening. This is why putty pads are specified in STC-rated assemblies even when fire rating is not the primary concern. The mass and seal of the pad restores the acoustic performance that the electrical box opening would otherwise degrade.
Installation
Putty pad installation is straightforward and does not require special tools or training. The pad is non-curing, so it stays soft and repositionable. You can install it before or after wiring.
Step-by-Step
- Remove the electrical box faceplate (if already installed)
- Peel the putty pad from its release liner
- Mold the pad around the back and sides of the electrical box, pressing firmly to eliminate air gaps
- Fold the edges over the rim of the box to create a complete seal
- Press firmly along all surfaces to ensure full contact with the box and the surrounding wallboard
- Reinstall the faceplate
Some UL listings specify wrapping the outside of the box before installing it in the wall. Others allow application after the box is mounted. Always follow the tested assembly detail for your specific wall design.
Tip: Because the putty is non-curing, you can reposition it if you need to pull wires or make changes after installation. Just re-mold the pad back into place when you are done.
Do not cut or trim putty pads to fit. Use the full pad as tested. Partial coverage voids the UL listing and will fail inspection.
Specifications
Everkem Flame Tech Putty Pads are designed for standard single-gang electrical boxes in fire-rated and STC-rated wall assemblies.
| Property | Value |
|---|---|
| Size | 7" x 7" x 1/8" |
| Listing | UL Classified |
| Fire test | ASTM E84 |
| Sound test | ASTM E90 |
| STC rating | Maintains 60 STC |
| Curing | Non-curing, stays soft and repositionable |
| Shelf life | Long shelf life (no expiration when stored properly) |
| Case quantity | 20 pads per case |
Tip: Order by the case for commercial jobs. A typical hotel floor can have dozens of boxes per fire-rated corridor wall. Count every outlet, switch, and junction box in fire-rated partitions during takeoff so you do not run short during rough-in.
Common Inspection Failures
Fire inspectors and special inspectors check putty pad installation as part of the firestop inspection. These are the issues that come up most often. For a full overview of what inspectors look for across all firestop systems, see the Firestop Inspection Requirements page.
| Issue | Why It Fails | Fix |
|---|---|---|
| Putty pad missing entirely | No firestop protection at the penetration | Install pad before covering the box |
| Pad on front of box instead of back | Does not seal the penetration through the wall cavity | Remove and reapply to back and sides of box |
| Pad trimmed or torn | Partial coverage voids the UL listing | Replace with a full, untrimmed pad |
| Back-to-back boxes without proper spacing | Code requires minimum 24" horizontal separation between boxes on opposite sides of a fire-rated wall | Relocate one box to meet spacing or use a listed solution for closer spacing |
| Wrong product used | Regular caulk or non-intumescent material has no fire rating | Remove and replace with UL Classified putty pads |
Watch for this: The most expensive failure is discovering missing putty pads after drywall is finished. At that point, you are cutting open walls to access the boxes. Build putty pad installation into the rough-in checklist so it happens before the wallboard goes up.
Putty Pads vs Firestop Sealant
Putty pads and firestop sealants are both used to maintain fire ratings at penetrations, but they solve different problems. Here is when to use each.
| Application | Best Product | Why |
|---|---|---|
| Electrical boxes in fire-rated walls | Putty pads | Purpose-built, fastest installation, clean for inspectors |
| Pipe penetrations through fire-rated assemblies | Firestop sealant (e.g., Firestop-814+) | Fills annular space around pipes and conduit |
| Conduit penetrations | Firestop sealant | Seals the gap between conduit and the rated assembly |
| Cable bundles through fire-rated walls | Firestop sealant or pillows | Accommodates multiple cables in a single opening |
| Construction joints in fire-rated assemblies | Firestop sealant | Linear joints between wall and floor/deck |
Some UL listings allow firestop sealant around electrical boxes instead of putty pads, but pads are faster to install and provide a more consistent result that inspectors can verify at a glance. For pipe and conduit penetrations, see the Firestop Product Selection Guide for detailed product recommendations. For sealant chemistry and general selection, the Sealant and Caulking Selection Guide covers the full landscape.
Frequently Asked Questions
Do I need putty pads in my house?
Usually no. Putty pads are required in fire-rated and STC-rated wall assemblies, which are found in commercial buildings, multi-family housing, and mixed-use construction. Standard interior walls in single-family homes are not fire-rated. If your local code or HOA requires fire-rated walls between attached units (townhomes, duplexes), then yes, those walls need putty pads on every box.
Can I use regular caulk instead of putty pads?
No. Putty pads are UL Classified intumescent products tested to maintain the fire rating of the specific wall assembly. Regular caulk has no fire rating and will not expand to seal the opening in a fire. Using non-rated caulk where putty pads are required will fail inspection and leaves the building unprotected.
Do putty pads go on the inside or outside of the box?
It depends on the UL listing for your wall assembly. Most commonly, the pad wraps around the back and sides of the box on the cavity side. Some listings specify the pad goes on the room side. Always follow the tested assembly detail. If you are not sure, check the UL design number on the wall section of the drawings.
How many putty pads do I need per box?
One pad per box for standard single-gang boxes. Double-gang boxes may need two pads or a larger pad to cover the full area. Check the UL listing for your assembly, as it specifies the pad size and coverage required for each box size.
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