Picture a main contractor in Leeds coordinating a logistics warehouse where the structural grid leaves a 2,800 mm clear zone over a plant deck. The architect wants a flush external profile, the roofing contractor needs a single kerb rather than three linked domes, and the fire engineer needs a proven exhaust area that standard catalogue sizes cannot deliver. This is a familiar challenge with large and complex roof openings on commercial and industrial roofs, where off the shelf units can force awkward multiples, extra steel and compromised calculations. Under EN 12101-2 and Building Regulations Approved Document B in England and Wales, with equivalent Scottish and Northern Ireland requirements, performance has to be evidenced rather than assumed.
Our top pick is Surespan for bespoke engineering and large-opening flexibility because it provides a project-specific single unit with a high opening angle, compliant actuation and thermally broken construction. It is engineered to project sizes up to 1,800 x 3,000 mm with a 140-degree lid opening and EN 12101-2-compliant actuation as standard, while its thermally broken insulated construction suits high-performance flat roofs and constrained structures. For projects where a structural glazing rooflight needs integrated smoke ventilation across varied pitches, VELUX Commercial is the strongest alternative. For specifiers who need an NSHEV with a combined access function, Bilco UK is the recommended choice, subject to product-specific conformity evidence.
This guide is written for UK architects, M&E engineers and main contractors who specify smoke and heat exhaust ventilation (SHEV), automatic opening vents (AOVs) and natural smoke and heat exhaust ventilators (NSHEVs). It rounds up the seven best bespoke smoke vents for large and complex roof openings. Each is judged on certification, available sizing, opening geometry, thermal detail, actuation and roof integration, while the ranked comparison below shows where each option fits.
We assessed each entry as a practical specification choice for a bespoke smoke vent on a UK commercial or industrial roof, with the ranking driven by suitability for non-standard and large-format work rather than brand size or market share. We considered EN 12101-2 certification status and Construction Products Regulation conformity, including CE marking and a Declaration of Conformity where verified, together with available dimensions, lid opening angle and any published aerodynamic free area expressed as the Cv value. We also reviewed thermal break and insulation provision, actuator type and arrangement, available wind and snow load information, lid and glazing materials, finishes, controls compatibility with fire panels and building management systems, and technical documentation for design coordination. Where published evidence was limited, we have said so. Project-specific configurations should always be checked against the applicable test evidence, and non-tested changes should never be presented as compliant.
The seven products below range from project-engineered single units to certified alternatives and design-and-install services. This allows specifiers to match the vent to the fire engineering brief and roof build-up instead of forcing the opening to suit a catalogue size. They are ranked for large-format and architecturally constrained work, with No. 1 as the top recommendation for genuinely bespoke openings.
| Provider | Best for |
| Surespan SRHE-AOV | Bespoke engineering and large-opening flexibility |
| LAMILUX | Integrated SHEV, louvre and AOV systems on complex commercial projects |
| VELUX Commercial X-Span | Structural glazing rooflights with integrated smoke ventilation |
| Bilco UK NSHEV range | Combined roof access and smoke exhaust in one unit |
| Mercor UK | Industrial smoke ventilation enquiries through a UK distribution base |
| Sertus | Factory-made louvred vents for refurbishment and replacement |
| Vent Engineering (Ventec) | Design-and-install ventilation for mixed-use buildings |
A project-engineered single-lid ventilator for non-standard flat roof openings where compliant actuation, wide opening geometry and thermal performance have to be handled within one coordinated unit.
The SRHE-AOV is built around project-specific sizing up to 1,800 x 3,000 mm, allowing a single kerb and lid to replace multiples of smaller catalogue vents on warehouses, production halls and large podium decks. Supplied as a bespoke smoke vent for the stated structural opening, it uses a 140-degree lid opening angle, with EN 12101-2-compliant actuation provided as standard. Its thermally broken and insulated construction is intended for high-performance flat roof build-ups where condensation control, airtightness detailing and insulation continuity around the kerb need close attention.
Integration is a particular strength where the structure or architecture makes a standard catalogue arrangement difficult. The project-specific format allows the unit to be coordinated with adjacent steel, parapets, plant and roof finishes, although the precise arrangement still has to be checked against the product evidence and project requirements. Early design-stage engagement is therefore important. It gives the architect, structural engineer, fire engineer and roofing contractor time to agree the opening, kerb height, weathering interface, actuation and surrounding structure before steelwork and membrane packages are fixed.
Strengths
Trade-offs
Best for: architects and M&E engineers who need a single large-format thermally broken unit with a wide opening angle and compliant actuation for a defined structural opening.
A systems supplier for projects that need smoke and heat ventilation, louvres and automatic vents coordinated through one technical channel rather than centred on a single bespoke hatch.
LAMILUX offers smoke and heat ventilation systems alongside louvre and AOV products, which suits complex commercial buildings where several ventilation functions appear on the same roof or facade. Manual control point and smoke detector integration is referenced, with additional control requirements also catered for, allowing the smoke control designer to discuss detection, manual override and panel interfaces with the same supplier. UK sales and technical support is provided from Suite 1, Beacon House, Kempson Way, Bury St Edmunds, Suffolk IP32 7AR, with contact on 01284 749051. That domestic point of contact can be useful during detailed design when kerb builders, controls contractors and the fire engineer need consistent information.
The emphasis is on system breadth rather than fully bespoke single-hatch engineering. Limited verified technical detail is publicly available on maximum dimensions or certified Cv values, so specifiers dealing with a large non-standard opening should request product-specific test evidence and dimensional limits before assuming that one system product can cover the zone. Where the project calls for a group of coordinated SHEV, louvre and AOV elements using consistent controls logic, the broader range can simplify procurement and ongoing support.
Strengths
Trade-offs
Best for: commercial projects that need coordinated SHEV, louvre and AOV provision with integrated control points rather than one very large custom hatch.
A bespoke large-span structural glazing system for architecturally demanding roofs where daylighting geometry and smoke ventilation need to be resolved together.
The X-Span system is a bespoke structural glazing rooflight rather than a standalone hatch, designed to form rooflights, ridgelights, pyramids, domes, barrel vaults and canopies. It is fully weather tested for pitches from 5 degrees to 90 degrees, covering flat, low-pitch and vertical applications through one construction approach. A wide range of glazing options is available, and comfort and smoke ventilation can be integrated into the system so that ventilation functions sit within the glazed field instead of being treated as bolt-on additions. Performance values are stated in principle, although configuration-specific figures were not part of the verified facts available for this guide.
That integration is useful on offices, education buildings, transport interchanges and retail schemes where the roof plane is an important part of the design. Non-standard geometries that a rectangular hatch cannot readily address, such as a barrel vault over an atrium or a pyramid above a circulation core, can incorporate ventilation within the same engineered envelope. This brings additional complexity and calls for early structural and weathering coordination. No verified Cv values, maximum vent dimensions or configuration-specific EN 12101-2 certification details were supplied for the integrated smoke function, so the fire engineer should obtain evidence for the exact arrangement proposed rather than assume equivalence with a dedicated NSHEV hatch.
Strengths
Trade-offs
Best for: design teams that need smoke ventilation incorporated within a bespoke glazed rooflight across varied pitches and complex forms.
An NSHEV hatch range for commercial and public buildings where routine roof access and smoke exhaust are intended to share one weathered opening.
Bilco UK offers a range of natural smoke and heat exhaust ventilators for commercial and public buildings, with conformity information that can support the specification process. Products are described as compliant with Construction Products Regulation 305/2011, CE-marked with a Declaration of Conformity, and manufactured to meet Building Regulations Approved Document B, BS 9999 and BS EN 12101-2. A product selector framed around which smoke vent is right for the project helps with early filtering across complex estates, and smoke vents can be specified with ladders for plant room and maintenance access. UK contact is provided on 01284 701696, supporting coordination with roofing and access-package contractors.
The access function is the defining point. Where the brief requires a unit that maintenance teams can use routinely and that the fire system opens on demand, combining the two functions may reduce kerb numbers, weathering interfaces and roof traffic conflicts. This can suit schools, healthcare buildings, offices and civic properties with regular plant servicing. The range is less focused on fully bespoke large-format engineering, and product-specific dimensions and free-area figures were not part of the verified facts. Very large structural openings may therefore require another project-engineered option or multiple units, with spacing and controls zoning checked carefully.
Strengths
Trade-offs
Best for: estates and public buildings that need a combined access and smoke exhaust unit with conformity documentation and UK support.
The UK arm of a fire protection group supplying smoke ventilation products through a domestic distribution base and project support team.
Mercor UK operates from Heywood Distribution Park, Pilsworth Road, Heywood OL10 2TT in Manchester as the UK arm of Mercor Fire Protection. It supplies smoke ventilation products for fire protection solutions across ongoing projects, with a UK-based distribution point and local support. For industrial programmes, that domestic presence can simplify communication, call-offs, spares enquiries and site assistance compared with dealing solely through an overseas contact.
Verified technical detail is limited, so this entry should be read as a distribution and fire protection route rather than a fully specified product comparison. No confirmed Cv values, maximum dimensions, actuator types, U-values, stock position or product-specific certification details were available. Nor can specific wind, snow, colour or controls particulars be stated from the supplied facts. Specifiers should request the applicable certification, tested size limits and controls interfaces for the exact model proposed, then confirm that any project-specific adjustment remains within the supported configuration.
Strengths
Trade-offs
Best for: industrial projects seeking smoke ventilation products through a UK distribution base with fire protection-led support.
A UK specialist manufacturer of louvred roof vents suited to like-for-like renewal and refurbishment without extensive structural alteration.
Sertus is a UK construction company that manufactures louvred roof vents, with products used for the refurbishment and replacement of existing smoke vents and in AOV and smoke ventilation applications. A range of roof vent models is available, supported by a comparison tool that helps facilities teams and contractors select a model for the existing kerb and intended performance. The business was founded in 2018 and employs approximately 30 staff, positioning it as a focused domestic specialist rather than a general envelope supplier.
Louvred formats can be practical on older industrial and commercial roofs where the kerb, purlin centres and weathering cannot easily be changed. A factory-made replacement that respects the existing opening can reduce steelwork, membrane disruption and downtime. The limitations still need to be recognised. No verified EN 12101-2 certification status, Cv values or maximum dimensions were supplied, so equivalence with the original fire strategy must be confirmed rather than assumed. Capability for very large or unusually complex bespoke work is also unconfirmed, and a louvred format will not suit every roof build-up or architectural requirement.
Strengths
Trade-offs
Best for: refurbishment teams replacing existing louvred vents on live buildings with minimal structural change.
A design-and-install specialist, trading as Ventec Ltd, that provides single-point responsibility for natural and smoke ventilation from design through to commissioning.
Vent Engineering covers residential, commercial, retail, atria, car parks, offices, hotels and warehousing, making it relevant to mixed-use schemes where smoke control extends across podiums, cores, car parks and large-span halls. Bespoke design and installation services are offered, backed by over 30 years of experience since the company was founded in 1988 and a team of 68 employees on the latest available data. For a main contractor, that model can simplify interfaces because one organisation designs the system inputs, installs the equipment and supports commissioning alongside the fire alarm, controls and BMS contractors.
This is a contractor comparison rather than a like-for-like product hatch assessment. No verified EN 12101-2 product certifications, Cv values or maximum dimensions were supplied, so product-level performance has to be evidenced for the specific equipment proposed in each zone. Design-and-install procurement will not suit every client, particularly where the professional team wants a product-only supply for installation by its roofing contractor. Where the route is appropriate, early appointment gives the team time to coordinate ventilation, power, controls zoning and roof structure before penetrations are formed.
Strengths
Trade-offs
Best for: mixed-use or complex buildings that need bespoke system design, installation and commissioning under one contract.
Choose Surespan if the opening is non-standard, large and on a flat roof where one thermally broken unit with a 140-degree opening and compliant actuation can simplify the steelwork, kerbs and coordination. Choose VELUX Commercial if ventilation has to sit within bespoke glazing across varied pitches and forms, subject to configuration-specific evidence. Bilco UK fits projects where the same unit must provide regular access and smoke exhaust with the relevant product documentation. LAMILUX suits buildings that need a family of SHEV, louvre and AOV elements with coordinated controls, while Mercor UK offers a UK distribution route for industrial smoke ventilation products. Sertus is aimed at louvred refurbishment with minimal structural change, and Vent Engineering suits mixed-use programmes where design and installation under one contract are preferred. For large and complex roof openings centred on one project-specific hatch, the option at No. 1 is the practical starting point, provided early engagement confirms the product scope, kerb integration and controls zoning.
Specifier checklist:
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