Most coop plans circulating online start from a floor area and work outwards. That is the wrong end. A coop is dimensioned by what each bird needs in linear centimetres of perch, feeder and drinker, and the floor area is what falls out of those numbers once you have them. Get the sequence right and a build stops being a compromise you live with for ten years.
Key takeaways
- Dimension from linear equipment allowances first, then derive the floor area. The reverse order is what produces crowding at the feeder in an otherwise legal house.
- Usable area and floor area are not the same thing. Only usable area counts against the 9 hens per m² figure.
- Broilers are governed by liveweight per m², not birds per m², and the threshold carries a notification obligation.
- Materials are chosen on how they survive five years of washing and disinfection, not on how they look at handover.
The reference figures, in the units the regulation uses
The numbers below come straight from the two directives that set minimum standards in the European Union, and they are the sensible baseline for any specification even where a holding is too small to be in scope. Keeping them in one place also avoids the common mistake of mixing a laying hen figure with a broiler figure in the same calculation.
| Provision | Minimum | Source |
|---|---|---|
| Stocking density, non-cage laying system | 9 hens per m² usable area | 1999/74/EC, Art. 4 |
| Perch | 15 cm per hen | 1999/74/EC |
| Nests | 1 per 7 hens, or 1 m² group nest per 120 hens max | 1999/74/EC |
| Littered area | 250 cm² per hen, litter over at least 1/3 of ground surface | 1999/74/EC |
| Feeder | 10 cm per bird linear, 4 cm per bird circular | 1999/74/EC |
| Drinker | 2.5 cm per hen continuous trough, 1 cm per hen circular | 1999/74/EC |
| Levels | 4 maximum, at least 45 cm headroom between them | 1999/74/EC |
| Broiler stocking density | 33 kg/m², up to 39 by derogation, 42 under Annex V conditions | 2007/43/EC |
One provision in the broiler directive is procedural rather than physical and gets forgotten at the planning stage. An operator intending to exceed 33 kg/m² has to notify the competent authority of the exact figure, and of any change, at least 15 days before the flock is placed. A building sized for 39 kg/m² therefore commits you to an administrative routine as well as to additional technical requirements.
Why usable area is the figure that trips people up
Usable area is not the same as the footprint you measure on the slab, and the difference decides whether a house is compliant. Space occupied by nests, and areas without the required headroom, do not count towards the usable area against which the nine hens per m² is calculated. This is precisely why multi-tier systems are attractive: they add usable area without adding building envelope, provided each level keeps its 45 cm of clearance and the flock can move between levels without obstruction.
Our practical advice is to draw the usable area as a separate hatched layer on the plan, with nests and low-clearance zones excluded, and to put the bird number on that layer only. A plan that shows one area figure invites the wrong conversation with the builder.
Materials, judged on five years rather than on handover day
The selection criterion that matters for a professional build is how a surface behaves after repeated washing and disinfection, because that is what will happen to it several times a year. On that criterion the ranking is fairly stable:
- Untreated softwood absorbs water and organic matter, and once the grain opens it becomes impossible to disinfect to a verifiable standard. Acceptable for external cladding, poor for internal surfaces in contact with birds or litter.
- Sealed or coated plywood and composite panels hold up well provided every cut edge is sealed. Unsealed edges are the first thing to fail, and they fail where you cannot see them.
- Galvanised or coated steel tolerates high pressure washing and most disinfectant classes, at the cost of thermal bridging that has to be managed in the insulation design.
- Concrete floor with a coved junction to the wall is the single detail that most reduces cleaning time, because it removes the right-angle seam where organic matter accumulates.
- Welded mesh rather than hexagonal netting for any perimeter with a predator risk. Hexagonal netting resists containment, not intrusion, and the difference is measured in wire gauge and aperture rather than in appearance.
Layout: the sequence that sets your labour cost
Layout decides how many minutes a day the house costs to run, and that figure compounds over a building’s life far more than the capital cost of a wider door. Three arrangements do most of the work. Perches sit higher than the nest entrances, so that birds choose the perch to roost and stop fouling the nests. Feeders and drinkers sit away from the area under the perches, for the same reason. And the litter area sits where a machine can reach it, because a littered zone that has to be cleared by hand will be cleared late.
Access dimensions deserve one deliberate decision rather than a default. Doors wide enough for the widest piece of equipment that will ever enter, including the one you plan to buy in three years, cost very little at the framing stage and are close to impossible to retrofit.
Ventilation, the constraint that overrides the plan
Ventilation is not an accessory to the layout, it is a boundary condition on it. The thermoneutral range for chickens sits at roughly 19 to 22 °C, with the comfort range generally given as 20 to 25 °C, and production effects appearing above about 30 °C according to the assessments summarised by the EFSA panel on animal health and welfare. A layout that blocks airflow across the litter will produce wet litter and respiratory pressure regardless of how well the floor area was calculated. The technical detail behind that trade-off is set out in our article on air quality as a performance factor in poultry farming.
Water provision belongs to the same discussion, since drinker placement affects both intake and litter condition. As a working reference, birds drink roughly 1.8 to 2 times as much water as they eat by weight under normal conditions at around 21 °C, which gives a straightforward way to size the supply line and to detect a problem later from the daily water to feed ratio.
What we check before signing off a build
- Recalculate the bird number from the usable area layer, not from the floor plan, and compare it with the number in the contract.
- Measure total perch length, nest count, feeder length and drinker length against the flock size, individually. One of the four is usually short.
- Walk the cleaning route with a pressure washer in mind and mark every right-angle junction and hidden cavity.
- Confirm headroom between levels at the worst point, not the average, and check that birds have an unobstructed path between them.
- Check that the widest planned equipment passes through every door on its route, loaded.
None of those five checks needs a consultant, and together they take an afternoon. What they buy is the ability to correct a dimension while it is still a line on a drawing, which is the only stage at which correcting it is cheap.
The part of the specification that sits outdoors
Interior dimensions are half the picture. The run determines how much of the flock’s day is spent using the space you paid for, and it follows its own design logic.
Sources: Council Directive 1999/74/EC laying down minimum standards for the protection of laying hens, Article 4 and Annex (alternative systems); Council Directive 2007/43/EC laying down minimum rules for the protection of chickens kept for meat production, stocking density provisions and Annex V; EFSA Panel on Animal Health and Animal Welfare, welfare of laying hens on farm (EFSA Journal, 2023); published broiler water consumption references for the water to feed ratio. Consulted August 2026. National transposition may set stricter requirements than the directive minima.
Published previously, fully revised on 7 August 2026. General technical guidance for poultry professionals. Verify the requirements applicable to your holding with your competent authority before committing to a build, and refer clinical or flock health questions to a qualified poultry veterinarian.