MEP Penetration Details: Fire-Rated, Acoustic, and Waterproof Requirements

The Quick Answer

MEP penetrations through fire-rated walls, floors, or ceilings must be firestopped using a UL-listed system (ASTM E814 / UL 1479 tested). The listing is selected based on the assembly rating, penetrant type, annular space, and wall/floor construction. The design drawings must call out the listing number, and the contractor must install exactly that listing.

Fire-Rated Penetrations

A compliant fire-rated penetration detail must specify:

• Assembly rating: 1-hour, 2-hour, or 3-hour, matching the wall/floor it penetrates
• F-rating and T-rating: F (flame spread) ≥ assembly rating; T (temperature rise) often required by code for floor penetrations
• Penetrant type: Steel pipe, copper pipe, PVC pipe, insulated copper, steel conduit, cable tray, etc.
• Nominal penetrant size: Specific to listing (e.g., 2" max copper, 6" max steel)
• Annular space: Gap between penetrant and opening (min/max per listing)
• Firestop material and thickness: Sealant, putty, wrap, collar, or mortar, with specific depth
• UL listing number: For example, UL W-L-1234 for a wall-to-liquid-tight penetration

Reference NFPA sprinkler requirements for how sprinkler penetrations coordinate with firestopping.

Acoustic Penetrations

Acoustic-rated assemblies (STC 50+, STC 60+) require penetrations that preserve the sound barrier. Required detail elements:

• Non-hardening acoustic sealant at the annular space (typically both sides)
• Dampened or resilient sleeves for plumbing risers that pass through demising walls
• Back-to-back outlet box offsets—minimum 24" separation per IBC Table 722.6.3.1.1
• Acoustic putty pads on electrical boxes in STC-rated walls

If the wall is both fire-rated AND acoustic-rated, the firestop system must be listed with acoustic performance data, or a tested combined system must be used.

Waterproof Penetrations (Roof, Slab, Below-Grade)

Roof penetrations and below-grade penetrations must be waterproof before any firestopping is applied:

• Roof: Manufacturer-specific flashing boot (EPDM, lead, or mechanical rubber boot) integrated with the roofing membrane
• Slab-on-grade: Waterstop (PVC or hydrophilic) plus sealant after slab cures
• Below-grade walls: Link-seal mechanical penetration sleeves with rubber links tightened to compress against the sleeve
• Elevated slab (water above): Integrated flashing with the waterproofing membrane, sealed before overlying slab topping

See our waterproofing details guide for how these integrate with the overall envelope.

Drawing the Detail Correctly

Penetration details typically appear on a dedicated architectural detail sheet and on the structural, mechanical, electrical, and plumbing drawings. A complete design package will show:

• A typical penetration detail keyed to each listing
• A penetration schedule with location, assembly, penetrant, and listing number
• MEP drawings showing sleeves in reinforced concrete at every known penetration
• A specification section (07 84 00 Firestopping) with submittal requirements for listed systems

Common Drawing Review Errors

• "Firestop per UL listing" without a specific listing number—leaves field choice and creates AHJ disputes
• Listing selected for wrong penetrant type (insulated copper vs. bare copper)
• Missing T-rating requirement on floor penetrations in multi-story buildings
• Acoustic-rated wall with a fire-only firestop system (no acoustic performance data)
• Below-grade waterproof penetration shown with only firestopping—no link-seal or waterstop

Related: firestopping coordination and our QA/QC checklist.