South Farnham School, Farnham, Surrey — replacement of external kitchen extract ductwork after failed weather protection allowed water into the ductwork, which was then leaking into the kitchen through the extract canopy. Completed in three weeks.
The symptom was in the kitchen. The fault was on the roof.
Water was entering the school kitchen through the extract canopy. A canopy leaking water is an immediate problem in a food preparation area, and one that has to be resolved rather than managed.
The cause was not the canopy. The external weather protection and insulation on the ductwork serving it had failed, allowing water into the ductwork itself. Once inside, the ductwork carried it down and it appeared at the canopy — the lowest point and the only place anyone could see it.
This is a common pattern with external ductwork. The visible symptom is often a long way from the defect, and repairing at the point where water appears does not stop it.
Strip-out
The equipment was isolated, and the PIB rubber weather protection and insulation were removed and disposed of. That exposed the condition of the ductwork underneath and confirmed the extent of the replacement required.
New ductwork
New ductwork was manufactured and installed by our engineers. All joints were resealed with new butyl gaskets to ensure the soundness of the ductwork — on a kitchen extract system, joint integrity is what keeps grease-laden air inside the duct and rainwater outside it.
The ductwork was then thermally insulated with 40mm Kingspan Thermaduct boards. The boards were taped, glued and sealed into position, then finished with Gloss Black Pro clad 150TM to match the materials already installed on the ductwork on the roof above.
Matching the existing finish mattered here. The ductwork is visible, and a repair in a different material reads as a patch for the life of the installation.
Delivering it around a working school kitchen
A school kitchen cannot stop for three weeks. The extract system serving it has to be back in service for the kitchen to operate, which sets the programme for work of this kind regardless of how much ductwork is involved.
Scope of works
- Isolation of the existing equipment
- Removal and disposal of the PIB rubber weather protection and insulation
- Manufacture and installation of new replacement ductwork
- All joints resealed with new butyl gaskets
- Thermal insulation with 40mm Kingspan Thermaduct boards, taped, glued and sealed
- Finished with Gloss Black Pro clad 150TM to match the existing rooftop ductwork
Kitchen extract systems sit within the commercial ventilation and HVAC work ComGas carries out, and specifically within our commercial kitchen and catering capability. Ductwork of this kind is a recurring requirement across the education estate, where kitchens run to a fixed daily timetable.
