A fish processing hall is usually described as a wet building. It is more useful to describe it as a cold building with a wet floor, because the two descriptions produce different drawings.
If you design it as wet, you spend your attention on drainage, washdown and corrosion, and you end up with a hoseable shed whose cold rooms do not work. If you design it as cold, you start from the envelope, the thermal breaks and the condensation risk — and then you discover that the floor has to take water at the same time. Both have to be true at once, and the order in which you settle them is what decides the building.
1. Start from the dock edge and work backwards
Almost every fish hall is organised around the moment the product arrives: a door, a dock, a floor level, and a short route to either processing or freezing.
That single interface sets more of the building than the processing area does. The dock has to be at truck bed height and able to take a loaded pallet truck, which means a defined edge, a defined fall away from the door, and a canopy or an air lock if the door opens more than a few times an hour into a cold room. Product that arrives at ambient temperature and sits at the dock while the paperwork is done is product losing its cold chain in the most expensive place in the building.
Working backwards from the dock also produces the honest layout: receiving, then sorting, then processing, then freezing or chilling, then packing, then dispatch. Any step that goes back against that flow is a step that will be corrected with a temporary wall within two years.
2. Salt and humidity decide the protection, not the colour
A fish hall combines three things that are individually manageable and collectively hostile: humidity near saturation, salt carried in on product and on the floor, and washdown water that spreads both everywhere.
The protection decision is therefore a decision about exposure, not about appearance. Where the steel is washed directly and frequently, hot-dip galvanizing or a coating system selected for the project environment will both work, provided the choice is made per zone rather than once for the whole building. The top chord of a rafter over a dry packing area is not in the same environment as a column base beside a drain, and treating them the same either wastes money or loses the column.
What is not negotiable is the detail at the bottom of the building. A column that stands on a slab with water running past its base will corrode there long before the coating above it fails, and the fix is a raised base, a formed plinth and a floor that falls away from the steel rather than toward it.
3. The cold store is the smallest volume and the biggest risk
In a fish plant the freezer is often the smallest room on the plan and the one that decides whether the whole operation works.
Three details carry most of that risk. The thermal break at the slab edge, so cold does not travel out under the surrounding floor and heave it. The vapour barrier, continuous and on the warm side, so moisture does not migrate into the insulation and slowly turn it into ice. And the door, which in a fish plant is opened far more often than in any other cold store, because it sits between a wet room and a cold room and product crosses it constantly.
That last point changes the building: a freezer with heavy door traffic needs either an air lock or a vestibule, and the vestibule needs to be a room on the plan, not a curtain.
4. Insulation is a structural decision in a wet building
Panel thickness gets discussed as a thermal question. In a fish hall it is also a structural and a sequencing question.
Thicker panels are heavier, they need more support at the openings, and they change how the envelope is closed at the eaves and at the corners. In a building where the internal face will be washed, the panel joint detail also has to survive water running down it — which usually means a joint that drains outward and a fixing that does not sit in a pool.
The sequencing point is simpler and more often missed: a wet building should be closed before the floor is finished, not after. Water that gets under a floor during construction stays there.
5. Effluent volume, not effluent strength, is what breaks the drainage
Fish processing produces a lot of water with a lot of solids in it. Design attention usually goes to the treatment, and the building failure usually comes from the volume.
Two numbers decide whether the floor works: the peak flow during washdown, which is much higher than the average, and the number of gullies that peak flow is spread across. A hall with too few gullies does not drain slowly; it drains across the floor, which means water arrives at the far wall, at the base of the steel, and at the door of the cold room.
Grease and solids also mean the gullies need to be reachable, with baskets that can be lifted and cleaned by one person, rather than a slot in the floor that gets hosed at.
6. What I want before drawings
- The dock interface: vehicle type, frequency, floor level, and whether an air lock is possible.
- Product route from door to cold store, and how much of it crosses a temperature boundary.
- The cold room temperatures and door traffic, per room.
- The washdown method and where the water is allowed to go, including peak flow.
- Whether the building will later take a different species or a different product form.
- The wind speed to be used, taken from the applicable code at the project site rather than a round number, and the roof edge detail — an exposed coastal site is decided by its edge fixings and its openings, not by the frame section.
A fish hall is not difficult because it is wet. It is difficult because it is cold and wet at the same time, and the two requirements fight over the same floor.