Firestopping Cable Penetrations: What to Check After Low-Voltage Work in Your Building

After cable runs through a fire-rated wall or floor, check three things. Every opening must be sealed with a tested firestop system that matches that wall or floor. Sleeves must not be overfilled. Each penetration should be labeled. The trade that makes or reopens a penetration is usually responsible for firestopping it, but only if the contract says so in writing. This guide to firestopping cable penetrations covers what to look for, who owns the work and when an inspector will look at it.

What a penetration and a firestop are

A penetration is any hole made so something can pass through a wall, floor or ceiling. For low-voltage work, that usually means a bundle of data cable, a fiber run or a conduit going from one room or floor to the next.

A firestop is the tested system that seals that hole so the wall or floor still holds back fire and smoke. It can be a sealant, putty, wrap, pillow, block, collar or a manufactured pathway device that the cable passes through. Usually it is several of these used together in a set way.

There are two kinds of penetrations. A through-penetration passes all the way through the wall or floor. A membrane penetration breaks only one face of the wall, such as a box cut into one side of the drywall. Both can need firestopping in a rated wall.

Why openings in rated walls and floors must be sealed

Fire-rated walls and floors divide a building into compartments. That slows fire and smoke so people have time to get out and firefighters have time to work. A rated wall only does that job if it stays solid.

Once a hole is cut, the wall loses its rating at that spot until it is properly sealed. Cable jackets also burn, so a loose bundle in an open hole can carry fire and smoke into the next space.

The rule behind this comes from the building code your city has adopted. The City of Dallas lists its adopted construction codes on its website: the 2021 International Building Code and 2021 International Fire Code, both with Dallas amendments. Fort Worth’s site also lists the 2021 International Building and Fire Codes with local amendments. Other DFW cities adopt their own versions, so check with your city’s building department.

If you are building out a new space, firestopping belongs in the plan from the start. Our guide to planning cabling for a new office covers where rated walls and pathways fit in the bigger picture.

What to check after firestopping cable penetrations

You do not need to be a firestop expert to spot most problems. Walk the job with your contractor before the ceiling tiles go back in. Bring the drawings that show which walls and floors are rated.

Every opening is sealed, including the ones you can’t see

Most cable penetrations sit above the ceiling, in telecom rooms or in floor cores. Lift tiles along rated walls and look at both sides of each hole.

Look for:

• Open gaps around a cable bundle or sleeve
• Cable passing through a hole with no sleeve or seal at all
• Old holes from earlier work that were left open
• Firestop material that is cracked, pulled loose or pushed out of place

The right tested system for that wall or floor

This is the item owners most often miss. A firestop product has no rating on its own. The rating comes from the whole system: the type of wall or floor, what passes through it, and the exact products and steps used. That combination is tested to standards such as UL 1479 or ASTM E814 and published as a listed system with its own number. A Cabling Installation & Maintenance article explains how through-penetration firestop systems are tested and rated.

Ask the contractor for the system number used at each kind of penetration and the manufacturer’s drawing for it. Then check that:

• The system is listed for that wall or floor type. A system tested in a concrete floor does not cover a drywall wall.
• Its F rating (how long it stops flame) is at least the rating of the wall or floor. Some codes also require a T rating, which measures heat passing through.
• The products installed match the products named in the system. Mixing brands, or using a product that isn’t part of the system, voids the listing.
• The cable type, bundle size, sleeve size and gap around the cable fall inside the limits the system allows.

General-purpose caulk and spray foam from a hardware store are not firestop systems, even if the can is red.

Sleeves and pathways are not overfilled

Every listed system sets a cable fill limit for the sleeve or pathway device. Too much cable leaves no room for the seal to work. Fill limits vary, so the number to check against is the one in the tested system. One trade article on practical firestopping tips advises adding a new sleeve when one gets close to 50 percent fill, rather than packing more cable in.

Penetrations in floors deserve extra attention. Vertical backbone runs between telecom rooms are where many cables share one opening. Plan spare sleeves early, as covered in our article on structured cabling backbone planning.

Labels at each penetration

A label next to the penetration tells the next person what is there and who did it. That same trade article recommends marking the company name, date and number of cables. Many owners also ask for the listed system number on the label. Labels are useful even where your city does not require them, because they show who touched a penetration last.

Resealing after later cable is added

Firestopping is not a one-time job. Each new cable for a wireless access point, camera or desk drop can break the seal. Putty gets pushed aside, and a hole gets reopened and left that way.

Ask whoever adds cable later to reseal every penetration they open, with a system listed for the new cable count. Some manufacturers make re-enterable pathway devices that let you add or remove cable without rebuilding the seal. They are worth asking about in telecom rooms where cable changes often.

Removing cable leaves holes too. When old cable comes out under a cleanup project, as described in our post on removing abandoned cable under the NEC, the empty openings still need to be sealed.

Keep in mind that the cable’s fire rating and the firestop are two separate things. Plenum or riser cable is rated for the space it runs in, but it still needs a firestop where it passes through a rated wall or floor. Our article on plenum vs riser cable ratings explains the difference.

Paperwork you should keep

Before you close out the job, ask for:

• The listed system drawings used, matched to locations
• Photos of each penetration after sealing, taken before ceilings close
• Product data sheets for the firestop materials
• A marked-up floor plan showing where penetrations are

This record helps the next contractor and gives you something to show an inspector.

Who is responsible, and how to put it in the contract

On most commercial jobs, the trade that makes a penetration is expected to firestop it. That means the cabling contractor seals its own holes, the electrician seals theirs, and so on. On larger projects, the general contractor may hire one firestop subcontractor to handle every trade’s penetrations.

Problems start when nobody writes this down. A cabling crew may assume another trade will seal the holes, while the general contractor assumes the cabling crew did it. Sharing an opening causes trouble too. Some inspectors hold the last contractor through a penetration responsible for every cable in it, according to the same practical tips article.

To avoid gaps, put these points in the scope of work or contract:

• Who firestops each penetration the contractor makes, reuses or disturbs
• That all firestopping uses a listed system for the wall or floor type, with system drawings submitted before work starts
• That existing open penetrations found along the route are reported, and who pays to seal them
• Labels at each penetration and photos before ceilings close
• Who pays to fix the work if an inspector rejects it

If a contractor does not firestop, the contract should say so, and name who will. This is general guidance, not legal advice, so have your own counsel or project manager review the final language.

When inspectors check

On new construction and tenant finish-outs, the city building inspector usually looks at rated walls and penetrations before the ceiling is closed. If a penetration is open or sealed the wrong way, expect a failed inspection and a return visit. In bad cases an inspector may order cables pulled and the wall sleeved.

Some buildings get closer review. UL notes that the International Building Code calls for special inspection of firestop systems in high-rise buildings and in buildings in higher risk categories, such as hospitals. In those cases an approved inspection agency checks the work against ASTM E2174 or ASTM E2393.

Existing buildings are inspected too. Fire codes require firestop systems to be maintained, so a fire inspector can cite open or damaged penetrations long after the original job closed.

If you are planning new cable runs through rated walls or floors, make firestopping part of the scope from the first walk-through. You can review what goes into our structured cabling installation services and ask how firestopping will be handled on your job.