Buying Fire Alarm Systems for Blocks of Flats: What Agents Should Commission
By the DC Fire & Security engineering team — installing and maintaining fire and security systems since 2010. Updated June 2026.
Quick answer
Block fire alarm buying starts with strategy, not hardware: purpose-built stay-put blocks usually need no communal alarm (detection serves AOVs only), converted buildings commonly need Grade A mixed systems, simultaneous-evacuation buildings need full coverage now, and 18m+ newer buildings carry BS 8629 evacuation alert kit. Commission the fire risk assessment's conclusion — never a contractor's habit.
Match the system to the building's strategy
The full strategy logic — why communal alarms harm stay-put buildings, what AOV detection is, when strategies flip — lives in our communal fire alarms guide; this table is its procurement shadow.
| Building | Right provision | Typical cost |
|---|---|---|
| Purpose-built, stay-put intact | No communal alarm; in-flat BS 5839-6 detection; corridor detection only for AOV operation | AOV detection servicing/upgrades £500–£2,000 |
| Converted house (pre-1991 era) | Grade A mixed system: communal detection + heat in flats, all-sounding | £2,500–£6,000 typical conversions |
| Simultaneous evacuation (defects found) | Full BS 5839-1 coverage, flats + communal, usually wireless, monitored | £400–£700/flat equivalent; blocks £8,000–£25,000+ |
| 18m+/new-build era | BS 8629 evacuation alert system (fire service use) alongside strategy provision | From ~£8,000 small blocks upward |
The agent's commissioning discipline
Blocks buy fire systems badly when contractors prescribe before assessments conclude: the fire risk assessment (current, post-works, Fire Safety Act-scoped) names the provision; quotes then implement it — that order protects agents from both under-provision liability and the over-selling epidemic (communal alarms installed into stay-put blocks remain the sector's recurring own-goal, per the guide above). Specification hygiene for tenders: BS 5839-6 grade/category for conversions stated; wireless preference for occupied blocks justified (decant-free installs); monitoring decisions explicit (simultaneous-evacuation buildings: yes; AOV-only detection: signalling per design); resident-communication plans included (access for flat devices is the schedule risk); and certification deliverables itemised per the quote checklist. Section 20 thresholds catch most block fire projects — consultation-ready quote packs from bidders save a cycle.
Costs, BS 8629 and the maintenance estate
Money in agent-useful form: conversions to Grade A mixed systems £2,500–£6,000 typical (size/wireless dependent); simultaneous-evacuation retrofits effectively £400–£700/flat all-in (wireless, monitored — the waking-watch replacement economics the NFCC guidance anticipates; see the waking watch guide for that arithmetic); BS 8629 evacuation alert systems from ~£8,000 small blocks (fire-service-controlled, separate cabinet/loops — required new-build 18m+ and retrofitted under remediation schemes); AOV detection maintenance — the forgotten line — £300–£600/yr keeps the smoke-control system the FRA assumes. Maintenance estate thinking wins long-term: one provider across detection, AOVs, emergency lighting, door entry and (our combined model) security, one schedule, one compliance file per block — the compliance packages structure agents actually renew.
Frequently Asked Questions
A contractor says our stay-put block needs a communal alarm — true?
What are the corridor detectors for if not an alarm?
Who pays for BS 8629 in older tall buildings?
Can in-flat alarms be standardised across leaseholders?
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