What Is a Roof-Mounted AOV Smoke Vent — and Why Does Your Building Need One?

Introduction

If you work in roofing, fire protection, or building services, you already know the product. But for specifiers and developers coming to AOVs for the first time, the terminology alone can create confusion — AOV, SHEV, smoke vent, rooflight — these terms get used interchangeably on site and in specifications, and that confusion costs time.

This guide cuts through it. Here is what a roof-mounted AOV smoke vent is, what it must comply with, where it is required, and how to procure certified units without the back-and-forth.

What Does AOV Stand For?

AOV stands for Automatic Opening Vent. In the context of roof-mounted products, an AOV is a dome rooflight that automatically opens — triggered by a smoke detection signal or a manual override — to allow smoke and hot gases to escape from a burning building.

You may also see these products described as:

Smoke vents
SHEV units (Smoke and Heat Exhaust Ventilation)
Smoke vent rooflights
AOV rooflights or AOV dome rooflights

All refer to the same class of product. The key distinction between an AOV and a standard rooflight is certification: an AOV is tested and certified for smoke control performance. A standard rooflight is not.

How Does a Roof-Mounted AOV Work?

A roof-mounted AOV sits within a kerb assembly installed at roof level. Under normal conditions it acts as a standard rooflight, admitting daylight and allowing natural ventilation when required. In a fire event, one of the following triggers it to open automatically:

A signal from a smoke detector or fire alarm panel
A smoke control panel command (in panel-linked systems)
Manual activation via a breakglass or remote release

Once triggered, the vent opens — typically to 140 degrees or more — and creates a discharge path for smoke and toxic gases at high level. This buys evacuation time and keeps escape routes clearer for longer.

The Brett Martin Mardome Smoke Vent, for example, opens to 140° in under 60 seconds and is available in double or triple skin configurations. It can also be configured with an offset opening mechanism for use as a dual-purpose access hatch.

Key point for specifiers: AOVs in a SHEV system work in conjunction with inlet air — either through openable windows at low level, lobby dampers, or natural air paths. A vent in isolation does not constitute a system.

What is EN 12101-2?

EN 12101-2 : 2003 is the European standard governing smoke and heat exhaust ventilators. It specifies performance requirements, test methods, and marking requirements for natural smoke and heat exhaust ventilators (NSHEVs) — which includes roof-mounted AOV dome rooflights.

For a smoke vent to be compliant with UK building regulations in a smoke control system, it must carry EN 12101-2 certification. Products without it are not suitable for use as part of a certified smoke control scheme, regardless of appearance.

The Brett Martin Mardome Smoke Vent is fully certified to EN 12101-2 : 2003 and is manufactured in the UK.

When ordering, always confirm EN 12101-2 certification. Never accept a standard rooflight substituted into a smoke control specification.

Which Buildings Require Roof-Mounted AOV Smoke Vents?

Approved Document B (ADB) of the Building Regulations governs fire safety in England and Wales. Smoke control requirements are typically triggered in:

Single-staircase residential buildings above certain heights
Common corridors and lobbies in blocks of flats
Commercial and industrial premises where escape route protection is required
Basements and underground car parks
Atria and large volume spaces
Schools, hospitals, and other institutional buildings to specific design briefs

AOV systems in residential buildings often combine roof-mounted vents with lobby dampers — the AOV exhausts smoke from the common stairwell at high level while dampers isolate individual lobby areas. Both components must be specified and installed to work in coordination.

Polycarbonate or Glass — Which Dome for a Smoke Vent?

Most certified smoke vent dome rooflights use polycarbonate for the dome element. Polycarbonate is lighter, impact-resistant, and maintains structural integrity relevant to non-fragile classification.

Key considerations for material selection:

Non-fragile classification: The Brett Martin Mardome carries Class B non-fragile classification to ACR[M]001 when new and fully installed in accordance with the manufacturer’s instructions. This is critical for roof safety compliance.
Double or triple skin: Double-skin domes provide improved thermal performance. Triple-skin offers further U-value improvement for projects where energy performance is a consideration alongside smoke control.
Clear or opal: Opal domes diffuse light. Clear domes maximise daylight transmission. Both are available — confirm requirement with the specification.

How to Order Roof-Mounted AOV Smoke Vents

RamSpec AOV Solutions supplies certified EN 12101-2 smoke vents from Brett Martin (Mardome), Ventlux, and Vent Trade (Vent Engineering) — all available to order online at ramspecaov.co.uk.

The ordering process is straightforward:

Select the product and configuration from the product pages at ramspecaov.co.uk
Complete pro-forma payment online — all orders are pro-forma; nothing ships before payment
Delivery to site direct from the supplier — lead time is 10–15 working days

There are no minimum orders, no account opening procedures, and no waiting for a sales rep to call back. Trade professionals can get what they need, specified correctly, ordered efficiently.

Need a certified smoke vent for a current project? Browse the full range at ramspecaov.co.uk — EN 12101-2 certified units from Brett Martin, Ventlux, and Vent Trade.

Frequently Asked Questions

Can I use a standard rooflight as an AOV?

No. A standard rooflight has no certified smoke control performance and does not meet the requirements of EN 12101-2. Only products specifically tested and certified as smoke vents should be used in smoke control systems.

Do I need a smoke control panel with a roof-mounted AOV?

In most building applications, yes. AOVs in residential common areas are typically triggered by a smoke control panel linked to the fire alarm system. Stand-alone AOVs with local detection exist but are less common in multi-storey applications.

What is the lead time for AOV smoke vents?

Orders placed via ramspecaov.co.uk are fulfilled direct from the supplier. Standard lead time is 10–15 working days from confirmed order and payment.

Are AOVs required to be non-fragile?

Non-fragile classification is a roof safety requirement under CDM regulations, not directly a smoke control requirement. However, most reputable products carry a non-fragile rating. Always check the specific product data sheet and installation requirements.

About RamSpec AOV Solutions

RamSpec AOV Solutions is a trade-only online supplier of AOVs, smoke vents, smoke control panels, and rooflights. We supply products from Brett Martin (Mardome), Ventlux, and Vent Trade (Vent Engineering) — ordered online, fulfilled direct to site. No minimum orders, pro-forma payment, 10–15 working day lead time.