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How Much Does Fire Stopping Cost in a London Flat Renovation?

London flat fire stopping cost £45–£185/m² treated area + £85–£245 per penetration depending on service type. Intumescent mastic to small gaps £8–£18/m. Pillow + collar to large service penetrations £85–£245 each. Cementitious batt to large openings £125–£385/m². Critical at compartmentation walls + floors. Third-party FIRAS installer mandatory; certificate per penetration retained for golden thread.

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01

Compartmentation principle

Compartmentation = dividing a building into fire-resisting compartments to contain fire + smoke for evacuation + suppression time. Flat compartmentation typical: 60-minute fire resistance for floors + party walls + flat entrance compartmentation. Every penetration (cable, pipe, duct, structural beam) through a compartment line must be fire-stopped to restore the wall/floor fire rating. Common failure: post-installation services added without fire-stopping (extractor ducts, broadband, new electrical) — invalidates compartmentation. Major Grenfell finding + cause of subsequent rapid fire spread.

02

Fire-stopping products + applications

Intumescent mastic (Hilti CFS-S ACR, Sika Firestop): brushable + gun-applied; fills <30mm gaps around small services. £8–£18/m. Intumescent collar (Hilti CP643): wrap-around metal collar with intumescent insert for plastic pipe penetrations; expands on fire to seal pipe void. £45–£125 each. Intumescent pillow (Hilti CFS-PIL, Promat Promaseal-PL): cushion-style for large cable tray openings; remove for cable additions then re-stuff. £85–£245 each penetration. Cementitious batt (Promat Promaseal-S, Hilti CFS-CT): rigid board + sealant for large openings; permanent install. £125–£385/m². Mortar + ceramic fibre for cavities. All products must be third-party tested + installed per manufacturer data sheet.

03

When fire-stopping matters in renovation

Critical scenarios: (1) new extractor duct through compartment wall (cooker hood, bathroom fan) — duct penetration + fire damper; (2) new electrical cable run through floor void above neighbour's flat — service penetration + intumescent collar; (3) loft conversion party wall — re-establish 60-minute compartmentation across party wall fully to roof; (4) basement waterproofing service penetrations through floor slab — intumescent mastic + collar; (5) underfloor heating manifold penetrations + pipe routes between flats. FIRAS-certified installer required + certificate per penetration + photographic record in golden thread. Builderr uses Hilti + Promat systems on all multi-occupancy + HRB-adjacent projects.

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Do I need fire stopping for a single-family house extension?

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Compartmentation only required where compartment walls/floors exist (party walls, between dwellings). Single houses: party wall is compartmentation — any penetration through party wall must be fire-stopped (chimney removal, structural opening, services). Internal walls within single dwelling not compartmentation — fire-stopping not required.

Is fire-stopping the same as acoustic sealing?

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Related but different. Acoustic sealing closes air gaps for sound. Fire-stopping closes gaps + maintains fire resistance via intumescent/cementitious material that expands or chars under heat. Many products dual-rated (Hilti CFS-S ACR is acoustic + fire). Acoustic sealing alone (silicone mastic) NOT fire-rated.

What is the FIRAS scheme?

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FIRAS = Fire Industry Recognised Audit Scheme — third-party certification of fire-stopping installers. Members audited annually + competence assessed. Increasingly required by insurers + Building Control + Accountable Persons in HRBs. Builderr's specialist firestop subcontractor is FIRAS-registered.

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