Ask what destroys a poultry processing hall and most people answer with the obvious: moisture, blood, fat, chemicals. All true, and all of it arrives by one route — the washdown.
The steel frame is rarely the victim. A poultry hall that is ten years old and still sound is not one where better steel was bought. It is one where somebody decided, before the drawings, where water would land, where it would run, and what it would touch on the way out. That decision costs almost nothing at design stage and cannot be recovered later.
1. In a wet area the steel is fine; the joints are not
A galvanized or coated frame in a wet room is a known quantity. What fails is every place where one thing meets another: the base of a column, the fixing that holds a rail, the penetration where a pipe leaves a wall, the lap where a panel sits on a kerb.
Water does not need a gap. It needs a line — a lap, a ledge, a shadow gap, a screw head — and then capillary action and gravity do the rest. In a hall that is hosed down twice a day, every horizontal ledge is a reservoir and every downward-facing lap is a drip point.
So the practical rule is not "more coating". It is: no upward-facing ledges below about 2 m (6.5 ft), no fixing that traps water against a surface, and a plinth detail that lets water run off the wall rather than behind it. Above about 2 m the same rule still applies but the consequences are slower and easier to miss.
2. The ceiling is a machine support, not a lid
In poultry processing the roof structure is asked to carry things that were not in the original brief: shackle lines, overhead conveyors, ventilation ducts, washdown pipework, cable trays, and the occasional maintenance hoist that gets added three years later.
This matters for a steel building because the cheapest roof is the one with the lightest purlins, and light purlins do not like point loads appearing between them. Every future line needs a defined support line — a secondary steel beam on the rafter, drawn at the start, at the height the line will actually run.
Two numbers worth fixing early: the clear height from finished floor to the underside of the lowest obstruction, and the height of the monorail or line. In a hall with a 6 m (20 ft) eaves the usable clear height under the structure often lands closer to 4.5 m (15 ft) once ducting and pipework are added — which is the number the process engineer actually needs and rarely receives.
3. Water goes down, then sideways
Washdown water leaves the room by the floor, and the floor is where a poultry hall is decided.
Three tiers matter. The fall, which has to be continuous and steep enough to move solids as well as water — in the order of 1 in 100 rather than a token slope. The gullies, which have to be numerous enough that nobody hoses the same puddle twice, and positioned where the plant actually stands rather than where the grid suggests. And the kerbs and coving, which keep water in the wet zone and out of the dry storage behind it.
The failure I see most often is a floor that falls to a gully on the wrong side of a wall. It was drawn correctly, then the wall moved 600 mm (2 ft) during design development and the floor was not re-checked. Water then runs away from the drain and stands at the base of a column.
4. The cold side of the partition
Poultry halls almost always have a cold side: a chiller, a blast cell, a holding room. The partition between a warm wet room and a cold room is where condensation does its quiet damage.
Warm, humid air on one face, a cold surface on the other, and water forming inside the assembly where nobody can see it. The answer is a continuous vapour-tight layer on the warm side, an insulated panel that is thick enough to keep the cold face above the dew point, and — critically — no penetration through that assembly that is sealed with mastic alone.
The same logic applies to the roof over a cold room inside a larger shed: the cold ceiling needs its own vapour barrier and its own insulation, because the shed roof above it is not doing that job.
5. Dirty and clean ends must not share air
A processing hall is a pressure plan before it is a building. Air has to move from clean to dirty, deliberately, and never the other way.
For the steel building this translates into three things: where the supply and extract openings sit, whether openings can be closed off per zone so washing one area does not fog another, and whether the doors between zones are capable of being both a hygiene barrier and a route for a pallet truck.
That last one is a design conflict that is almost always resolved by buying a door that does neither job well. Better to decide the traffic route first and let the door follow.
6. What I want before drawings
- The process layout, including every line and every future line, with heights.
- The washdown method: hose pressure, water temperature, chemicals, and who does it.
- Where the wet zone ends and what is on the other side of that boundary.
- The cold rooms on plan, with their temperatures and their door traffic.
- Any point where the plant intends to add equipment above the floor later.
- The wind speed to be used, taken from the applicable code at the project site rather than a round number, and the roof fixing detail that goes with it — a wide, low hall with big openings is exactly the shape that generates local suction at the eaves, and the eave fixing is usually where a storm finds the weak point.
None of these are steel questions. All of them change the steel drawing, and none of them can be answered by a better coating.