What Is Firestop in Construction?

Firestop is a category of materials and assemblies designed to seal openings in fire-rated walls, floors, and ceilings while restoring the original fire rating. A firestop system consists of three components:

1. the rated wall, floor, or ceiling assembly being penetrated
2. the penetrating item, pipe, duct, cable, conduit, or cable tray
3. the firestop product, putty, caulk, mortar, intumescent collar, or pillow that seals the gap.

When correctly installed to a tested system, firestops prevent fire and smoke from passing through the penetration for the same duration as the unbroken wall. A 1-hour wall plus a correctly firestopped pipe penetration equals 1 hour of total fire resistance.

Ontario Building Code requires firestop at every penetration through a fire-rated assembly.

The most common scenarios in GTA construction:

1. plumbing drains, vents, and supply lines passing through party walls between dwelling units
2. electrical conduits and cables through rated walls and ceilings
3. HVAC ducts through rated separations (these usually need fire dampers, which is a related but separate system)
4. plumbing penetrations from a garage to a house above
5. ceiling penetrations between a garage and a room above
6. all penetrations in stairwell shaft walls
7. all penetrations in elevator shaft walls
8. any service penetration through a corridor wall in multi-unit residential.

For a typical Toronto townhouse, firestop is required at every plumbing, electrical, and HVAC penetration through the party walls between units, typically 15-30 penetrations per unit-to-unit boundary.

GTA contractors use a few standard products:

1. intumescent caulk, expands when heated to seal the gap; common around small electrical and plumbing penetrations
2. firestop putty pads, pre-formed putty pressed against and around penetrations
3. firestop pillows, fabric bags filled with intumescent material, used in larger openings or temporary penetrations
4. intumescent collars, wraps around plastic plumbing pipes that expand to crush the pipe and seal the opening when heated (PVC drains specifically need this)
5. firestop mortar, cement-like product for large openings, especially around HVAC ducts
6. sleeves and grommets, pre-engineered firestop assemblies for specific applications.

Products must be installed to a UL/ULC tested system specific to the wall assembly, the penetrating item, and the gap size. The catalog of tested systems is extensive, each penetration type has a specific tested detail.

Firestop is one of the most common rejection points at the framing-to-rough-in inspection.

Typical failures:

1. wrong product for the system, using general-purpose caulk where intumescent is required, or vice versa
2. wrong gap size, most firestop systems specify a maximum gap, and oversize openings need additional materials
3. PVC plastic plumbing without intumescent collars, PVC melts in fire and a non-intumescent firestop won't close the resulting hole
4. penetration too close to the edge of the rated assembly
5. multiple penetrations too close together, tested systems specify minimum spacing between penetrations
6. missing labels, some jurisdictions require visible firestop product labels on each installation.

Planning the firestop system at design stage, including specifying which products will be used at which penetrations, prevents most of these failures. Rough-in trades should be briefed on the firestop schedule before they start drilling.