Adequate ventilation is a must have for any shed, but where calves are involved, things become even trickier.
Due to their age, calf immunity is continually developing and is not helped by long distance haulage, time spent in a mart mixing with other calves and arriving to a new farm with additional health pressures.
Appropriate ventilation will go some way towards lessening the risk of diseases, with cool, fresh air coming in to the building being less likely to carry air borne diseases than warm, stale air.
The stack effect, where the animals’ body heat drives the warm stale air up and out of the outlet is less prevalent in calf houses as the young calves do not generate sufficient body heat to drive the air upwards.
Ventilation in calf sheds greater than 10m in width can also be difficult.
An air inlet of 0.08m²/calf should be left on normal sites; with exposed sites this can be reduced down to 0.05m².
In the case of calf houses, Yorkshire boarding, which is a double line of timber laths which are fixed offset to each other either side of a purlin, should be used as they give greater protection from the elements for calf housing.
An eave gap can also be left to act as an air inlet, though the roof structure will have to extend out over the side of the shed to protect this gap and prevent rain entering the shed.
Most farmers will opt for a ridge outlet with a cap on it. 50mm of ridge opening should be left for every 3m of building width, e.g. a 12m (40ft) wide shed will require 200mm of an outlet.
To sufficiently cover this outlet, the ridge cap should be 2.5 times the width of the outlet and raised above the sheeting approximately half of the outlet width.
In our example above of a 200mm outlet, the capping should be 500mm wide and raised 100mm above the sheeting of the roof.
Opening doors is not a good way to increase air inlet space, as a door opening is an unregulated air flow that will most likely do more damage than good by creating draughts in the shed.
Doors should only be opened to increase air inlet space on extremely calm, muggy days.
Roof height and pitch
Roof height and pitch are also factors in air regulation in calf housing. The air outlet (ridge opening) should be higher than 1.5m but less than 3m above that of the air inlet.
This is the reason that extremely wide calf sheds are difficult to ventilate properly, as the extra width creates extra height between the eaves and the ridge or creates a less than optimal roof pitch.
Pitch is also extremely important. A flatter pitch will fail to adequately funnel stale air out of the outlet and can cause air to be deflected downwards causing a draught.
Roof pitches should be 22° to properly funnel stale air out of the building through the ridge opening.
Where the roof pitch is too low, it may be necessary to use space sheeting on roofs, though again the poor stack effect created by young calves may lead to water ingress. Raising two sheets per bay might be a more appropriate option.