Firestop and Vapour Barrier at a Chilled-Water Penetration
A 100 mm chilled-water copper pipe, insulated with 25 mm closed-cell elastomeric insulation, passes through a 200 mm concrete block wall rated for 2 hours. The pipe OD is about 114 mm; with insulation the outside diameter is about 164 mm, leaving an annular space in a 200 mm sleeve. The existing firestop was removed during a renovation. A subcontractor proposes to fill the annular space with spray polyurethane foam, trim it flush, and paint the foam with intumescent paint. The chilled water runs at 4°C, so the pipe is cold and condensation is visible. The wall separates a corridor from an electrical room. The subcontractor says the foam is “fire-rated” and the paint will “make it compliant.” You must decide whether to accept the proposal, and how to deal with the vapour barrier and documentation.
1. Evaluate the subcontractor’s proposed firestop.
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Reject the proposal. A firestop must be a listed or tested system for the specific pipe material, insulation type, diameter, annular space, sleeve, and wall construction. Spray polyurethane foam plus intumescent paint is not a listed firestop assembly for this penetration, and “fire-rated” foam does not make an untested combination compliant. The foam may melt, shrink, or contribute fuel, and the paint does not create a tested seal. Require a listed firestop sealant or collar installed exactly to the manufacturer’s instructions, including the correct annular space and backing material. The reasoning is that fire separations are life-safety systems, and field improvisation can invalidate the rating.
2. How do you maintain the vapour barrier at the penetration while providing a firestop?
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Keep the closed-cell insulation continuous up to the firestop, seal the insulation ends and joints, and use a firestop sealant that is compatible with the insulation and listed for the assembly. If the listed firestop system permits, seal the annular space and the insulation-to-pipe interface to maintain vapour tightness without trapping water. Do not leave exposed cold surfaces or unsealed ends, because condensation will occur. Confirm that the sealant remains flexible and compatible at 4°C service. The reasoning is that the firestop and vapour barrier serve different functions but must coexist; a fire-rated seal that is vapour-permeable can still cause condensation and corrosion.
3. What documentation and inspection should be required before the wall is closed?
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Require the manufacturer’s listed system documentation, installation instructions, and evidence that the installer is qualified. Record the system name, sealant or collar type, annular space, insulation type, and wall rating. Inspect before concealment and photograph the penetration at each stage. Label the firestop and include it on the firestop schedule. Arrange inspection by the authority having jurisdiction if required, and retain records for the building owner. The reasoning is that concealed firestops are difficult to verify later, and documentation is the only reliable evidence that the assembly matches the tested system.