Kitchen extract supports must carry the duct, grease deposits, insulation and access loads independently while controlling vibration and allowing movement without opening grease-tight joints.
Installation boundary: This article explains design and coordination principles. Drainage, ventilation, fire, electrical and fabrication work must be designed and carried out by competent people using current project documents, manufacturer instructions and the requirements that apply in the relevant UK nation.
The short answer
Do not hang a grease extract from the canopy, fan casing or whatever building service happens to be nearby. A structural support design should identify weights, spans, anchors, fire-protection requirements, thermal movement and wind loading on external risers. Flexible connectors and anti-vibration mounts can reduce fan transmission, but they must be suitable for grease, temperature and fire duty and must not leave the fan or duct unstable.
Support loads are larger than the empty duct
The calculation should include sheet-metal weight, grease contamination allowance, insulation or fire enclosure, access doors, attenuators, treatment units and the forces created when panels are opened or cleaning equipment is used. External stacks also see wind loads. Roof curbs and frames must transfer those loads to suitable structure without crushing insulation or relying on waterproofing membranes.
Support spacing depends on duct size, construction, orientation and the selected system. A long horizontal run can deflect enough to create low points even if it does not visibly fail. Those low points collect grease and cleaning fluid, increasing weight further. Supports should maintain the intended geometry and remain accessible for inspection.
Separate vibration without losing control
Fan vibration can travel through rigid duct, steelwork and building fabric into bedrooms or offices. Anti-vibration mounts, flexible connectors and resilient support details need to be selected from fan speed, weight and forcing frequency. A generic rubber pad may provide little isolation or allow excessive movement at start-up.
Flexible connections must not sag into the airstream, trap grease or become the only restraint. Electrical isolators, weatherproof flexible cabling and maintenance clearances must tolerate the movement designed into the fan assembly. After installation, check vibration with all access panels, guards and final duct connections in place.
What common failures reveal
| Site symptom | Likely installation issue | Practical consequence |
|---|---|---|
| Grease appears at a joint | Duct deflection or thermal movement stresses the seam | Leakage and fire load outside duct |
| Bedroom hears low-frequency hum | Fan vibration bridges through duct or steel support | Noise complaints despite an attenuator |
| External riser moves in wind | Supports designed only for self-weight | Fatigue, noise and weathering failure |
| Flexible connector collapses | Wrong material, length or no independent fan restraint | Flow loss and grease trap |
| Roof membrane cracks | Loads or movement transferred into waterproofing detail | Water ingress |
Installation and coordination checklist
- Calculate duct, grease, insulation, component and maintenance loads.
- Verify anchors and frames against the actual building structure.
- Support fans and heavy treatment plant independently of adjoining duct.
- Allow thermal and structural movement without opening grease-tight joints.
- Select anti-vibration mounts from equipment data, not appearance.
- Use flexible connectors suitable for temperature, grease and required fire performance.
- Design external risers for wind and safe maintenance access.
- Inspect alignment, vibration and joint condition during commissioning.
Commissioning and handover
Include structural calculations or support schedules, anchor details, mount selections, flexible-connector data and roof-frame drawings. Record fan vibration or noise checks where required, and photograph concealed supports before enclosure. Maintenance instructions should identify mounts, connectors and joints that need periodic inspection—not only the fan motor.
Questions to ask before approving the work
- What loads are included beyond the empty duct?
- Which structural element takes each support?
- How is fan movement restrained?
- Does the flexible connector meet the grease and temperature duty?
- Who checks the external stack after high winds or maintenance?
Capture the installation detail before it becomes a site problem
Coordinate the installation, testing and handover items before the kitchen is signed off.
Technical sources and further reading
- HSE CAIS10: Ventilation of kitchens in catering establishments
- Bromley Council: Kitchen extraction planning requirements
- Approved Document B, Volume 2: Buildings other than dwellings
Last technical review: 14 August 2026. Always check the latest manufacturer instructions, statutory guidance, standards and project approvals before installation.