Phoenix Journal · Ductwork
When one extract riser serves several kitchens, the grease is shared but the blame rarely is. Here is how duct responsibility actually splits between landlord and tenants - and how to close the gap before a fire or an insurer does it for you.
Multi-tenant buildings
In a shared building, the kitchen extract system is often the one asset nobody feels they fully own - which is exactly why it becomes a problem.
A food court, a mixed retail and leisure scheme, a serviced office block with three cafes on the ground floor: in each case, grease-laden air from several kitchens can travel through the same risers, ceiling voids and roof-level fans. The moment a duct leaves a tenant's demise and runs through common parts, responsibility stops being obvious and starts being negotiated. Get that negotiation wrong and you are left with an uncleaned length of ductwork, a live fire path between units, and an insurer with a very reasonable question about whose certificate covers it.
Under the Regulatory Reform (Fire Safety) Order 2005 - amended by Section 156 of the Building Safety Act 2022 - a building can have more than one “responsible person”. Article 22 requires them to cooperate and coordinate. In practice, duties tend to divide like this.
The core issue is physical. Grease does not respect a lease plan. Vapour rises from a canopy, passes through the tenant's own duct, joins a common riser and travels to a shared fan - so a fire that starts in one unit's uncleaned section can spread through the whole run and into every unit connected to it. That is why the standard treats the extract as a single system from canopy to discharge, even when the ownership is split three or four ways.
BESA's TR19® Grease is the recognised UK specification for managing that risk. It asks you to keep grease deposits below a mean average of 200 microns between cleans, verified by a Deposit Thickness Test or Wet Film Thickness Test, and evidenced with before-and-after photographs from matching positions plus a post-clean hygiene report naming the technician and the date. Cleaning frequency follows use: heavy use of twelve to sixteen hours a day points to roughly every three months, moderate use of six to twelve hours to around six months, and light use to about twelve months. In a shared building, those frequencies rarely match - a busy grill unit and a quiet sandwich bar on the same riser will foul it at very different rates, which is precisely why one tenant cleaning to their own schedule does not make the shared section safe.
The fix is coordination, not heroics. First, map the system honestly: agree in writing which lengths sit inside each demise and which sit in common parts, and put that map in the front of every relevant fire risk assessment. Article 22 makes this cooperation a legal duty, so it is worth documenting rather than assuming. Second, appoint a single competent contractor to clean the shared runs and the roof plant as one job, with the cost apportioned through the service charge - it is faster, cheaper and far easier to evidence than four separate visits that each stop at an invisible boundary. Third, fix access: TR19® Grease expects access panels at regular intervals, typically every two to three metres wherever the layout allows, so that every internal surface can be reached, cleaned and photographed. A riser with no panels is not a cleaning problem, it is a design defect that will keep failing your verification.
Then keep the paperwork tidy on both sides. The landlord holds the certificate for the shared runs and roof plant; each tenant holds the certificate for their own demise; and the two sets read together should cover the whole system with no unclaimed length in between. This matters most at the worst possible moment. Insurers increasingly make TR19®-compliant cleaning a policy condition, and where a fire is linked to grease build-up and there is no valid, matching certificate, cover can be challenged or refused. In a shared building the danger doubles: a gap in the landlord's evidence can pull an innocent tenant into the loss, and a tenant who skipped a clean can expose the whole scheme. Everyone's defensibility depends on the weakest certificate on the riser.
None of this is complicated once someone owns it. The buildings that stay safe are the ones where the managing agent and the catering tenants treat the extract as shared infrastructure - mapped, scheduled, accessible and evidenced - rather than a boundary dispute waiting for an ignition source.
Questions
Responsibility usually splits: the landlord or managing agent is the responsible person for ductwork in the common parts, including shared risers and roof-level plant, while each catering tenant is responsible for the extract within their own demise. Under Article 22 of the Regulatory Reform (Fire Safety) Order 2005, all responsible persons must cooperate and coordinate. The cleanest approach is to map the system in writing and appoint one contractor for the shared sections, with costs apportioned through the service charge where the lease allows.
That is the classic gap. Horizontal runs crossing a ceiling void above a neighbour, or the middle of a vertical riser, are often too far from any single tenant and too kitchen-specific for the managing agent, so they get cleaned by nobody. Because grease from one unit passes through these shared lengths, an uncleaned section is a live fire path for every connected kitchen. The fix is to name that section in the fire risk assessments and hand it to a single contractor rather than leaving it to chance.
Yes, in effect each responsible person needs evidence covering the ductwork they are accountable for. The landlord holds certification for the shared runs and roof plant; each tenant needs post-clean documentation for their own demise to satisfy their own insurer. Read together, the certificates should cover the whole system from canopy to discharge with no unclaimed length in between. A gap in anyone's evidence can undermine cover for the whole building if a grease-related fire occurs.
TR19 Grease sets frequency by use: heavy use of twelve to sixteen hours a day points to around every three months, moderate use to about six months, and light use to roughly twelve months, all aiming to keep grease below a mean average of 200 microns. In a shared riser the busiest kitchen effectively sets the pace, because a quiet unit cleaning to its own light-use schedule will not keep the shared section safe. It is usually simplest to clean the whole shared run to the frequency the heaviest user demands.
Phoenix Duct Clean · by the numbers
Phoenix surveys and cleans kitchen and building ductwork to the TR19 standard - measured, cleaned and certificated, UK-wide.