Commercial kitchen drainage design: common problems to resolve before construction

Kitchen drainage has to follow the kitchen equipment, and the equipment often changes later than the rest of the design. Designing to an indicative layout and hoping it holds is a common cause of site changes.

The drainage design should be coordinated against the kitchen designer's equipment schedule, with each appliance's waste size, position, temperature and whether it discharges directly, via an air break, or to a floor gully clearly identified. Where equipment is not yet fixed, the design should record the assumptions made so changes can be checked quickly.

Dishwashers, combination ovens, ice machines, glass washers and similar equipment each have specific connection requirements. Some require indirect connection via tundishes or air gaps for hygiene reasons, and some discharge at high temperatures that affect pipe material selection.

Getting these details agreed early avoids the familiar site scenario of equipment arriving with an outlet in a different position or at a different height from the drainage provided.

Kitchen floors typically need gullies or channels, adequate falls to them, and falls onwards in the pipework below. In an existing unit the slab depth and any screed zone set hard limits on what is achievable.

Where the required falls cannot be achieved within the available zone, options include raised floors, localised slab breakout, relocating equipment, or pumped solutions. Each has cost, programme and structural implications that should be decided before construction, not discovered during it.

Grease-laden drainage will need maintenance. Rodding points and access covers should be provided at sensible intervals and positioned where they can actually be reached, which in a kitchen means not beneath fixed equipment or cold rooms.

Access positions should be coordinated with the kitchen layout and the floor finish specification so they survive to handover.

Fats, oils and grease entering drainage are a major cause of blockages in both private and public sewers, and sewerage undertakers take enforcement seriously. A FOG strategy should consider where grease is produced, how it is kept out of the system at source, and whether a grease separator or other treatment is required.

The most effective strategy is the one the operator will maintain. A separator placed where it cannot be emptied, or a system that relies on dosing no one will manage, will not perform in practice. Sizing, location, maintenance access and emptying arrangements need to be agreed with the operator.

New kitchens are frequently installed in units where the existing drainage was designed for a different use. Before relying on it, the route, size, falls and condition should be confirmed, and the connection to the landlord or public system understood.

In multi-occupancy buildings, existing kitchen drainage may be shared with other tenants. Capacity, access rights and responsibility for maintenance all need to be clear.

Floor channels, trenches, gullies and slab penetrations are builder's work items that need to be communicated in time for the contractor's programme. Kitchen drainage also interacts with ventilation, gas, water and electrical services at the equipment line.

Issuing clear builder's work information and reviewing it against the kitchen designer's and structural engineer's drawings closes most of the gaps that otherwise lead to late coring, patched slabs and compromised falls.

Late site fixes in kitchen drainage tend to reduce falls, remove access, or add pumped units that were never intended. They are usually the result of decisions deferred during design.

Resolving equipment connections, falls, FOG strategy and existing drainage condition before construction is the most reliable way to deliver a kitchen that opens on time and continues to operate without drainage problems.