Why Residential Flats Over 11m Need AOV
In a residential block, residents must be able to evacuate through the common stair without encountering life-threatening smoke concentrations. Below 11 m, natural ventilation of the stair via an openable vent at the top is often sufficient. Above 11 m, a powered AOV system with automatic smoke detection and actuation is required.
Following the Grenfell Tower fire and the resulting changes to building safety legislation, there is heightened scrutiny of smoke ventilation provision in residential blocks. The Building Safety Act 2022 creates additional obligations for buildings over 18 metres, including mandatory registration with the Building Safety Regulator and enhanced record-keeping.
What the Regulations Require
ADB Volume 1, clause 2.27 requires smoke ventilation of common corridors and lobbies in residential blocks above 11 m. The AOV system must achieve a minimum free area at the vent, and the stairwell must also be ventilated at the head. Battery backup must maintain operation for the required standby period.
BS 9991 provides the detailed design standard for residential AOV systems. It specifies vent sizing methodology, detector placement, wind pressure allowances for natural vents in exposed locations, and the interface between the AOV system and the building's fire alarm system. The 2024 amendment updated requirements for single-stair buildings and higher-risk buildings.
System Components for Residential Flats
A typical AOV system for a residential block consists of: an AOV roof vent at the head of the stair (minimum 1.0 m² GFA); AOV louvres or vents serving common corridors and lobbies at each floor; optical smoke detectors in corridors and lobbies; an AOV control panel with battery backup; and manual override push-button stations at each floor level.
Maintenance Obligations
Under the Regulatory Reform (Fire Safety) Order 2005, the Responsible Person of the residential block must ensure the AOV system is maintained. This means weekly visual checks, monthly functional tests, six-monthly full system tests, and annual inspections by a competent engineer. For buildings over 18 m, maintenance records must be kept as part of the building's Golden Thread of information.
Retrofit AOV for Existing Blocks
Retrofit AOV installations in existing residential blocks are common, particularly following post-Grenfell safety reviews and fire risk assessments that identify deficiencies. AOV Direct can supply complete systems including all components for retrofit applications. Our technical team can advise on the most appropriate approach for your building.
AOV Direct supplies complete AOV systems for residential blocks, including stairwell kits from £1,964 +VAT. Next day delivery. Call 01202 725 677 for project support.
Need Expert Advice?
Our engineers are available to advise on compliance and product selection.