Getting building ventilation right
Getting building ventilation right is critical to animal performance and welfare, as Jamie Robertson, honorary research fellow at Aberdeen University, explains…
Let’s start with a simple truth – most livestock buildings are not designed for purpose and ventilation is often overlooked or misunderstood. Yet poor ventilation has a massive impact on the incidence of respiratory disease; it increases moisture levels, which can lead to an increase in bacteria and disease; and escalates heat levels, leading to heat stress, particularly in the summer months.
Most natural ventilation works on the principle of providing a means for warm stale air to escape from the roof of the building, thereby drawing fresh, cool air into the sides of the building in its place – the so-called ‘stack effect’ caused by hot air rising. What good ventilation relies on, therefore, are sufficient air gaps at the ‘inlets’ – usually at the sides - and at the ‘outlets’, usually at the ridge of the roof. This must be done whilst protecting stock in the building from excessive draughts and inclement weather.
Getting ventilation right isn’t complicated and doesn’t have to add cost to your building. What’s more, the payback on investment in improving ventilation tends to be rapid. Here are some top tips to ensuring your buildings have sufficient natural ventilation:
1. Don’t assume that your new building will be ok
Too many farmers simply assume that a new building will provide acceptable ventilation, whereas often standard designs do not. This is not the fault of builders – generally they are selling on price and not performance and, unfortunately, most farmers don’t focus enough on ventilation to worry about it or ask for anything different. So the first tip is don’t assume it will be ok, which leads to…
2. Work out the inlet and outlet requirements based on the stock you are housing
Good ventilation is simply about getting sufficient inlet and outlet areas for the way the building is being used, and the main influence on this is the type, size and number of livestock being accommodated. Both DairyCo and EBLEX publish simple guides to working out air outlet requirements – so grab a calculator and work it out! Once you’ve established what the air outlet should be, make sure that the inlets are at least double the outlet area and preferably four times.
3. Design your ventilation for the specific building in question
There is no ‘one size fits all’ for good ventilation. Using the information you’ve calculated above, think about the best solution for the building in question.
When it comes to outlet ventilation, open ridges work best, particularly those with upstands like the Marley Eternit open ridge, as the upstand deflects the wind, creating negative pressure in the ridge – it is basically a free extractor fan that draws stale air from the building. If you are worried about rain ingress then look for a protected open ridge – again Marley Eternit’s is about the best in the business in terms of ventilation performance.
At all costs avoid the widely used vented ‘cranked’ ridges, as the outlet area these provide is completely inadequate for most circumstances, and under no circumstances fit a closed ridge. Slotted roofs have fallen out of favour but also work well, assuming there is sufficient outlet space across the whole roof.
When it comes to inlet ventilation, it should ideally be equally balanced down both sides of the building. It must control airspeed on windy days at animal level, but not too much or internal air will get stale on still days.
If you are on an exposed site then think about solid cladding with a suitably sized horizontal gap where sheets overlap the wall or under the eaves. Space boarding works fine but calculate the inlet area required to make sure that the amount is adequate; don't simply assume it will be ok. Flexible systems, such as Galebreaker or hinged panels, provide the optimum control.
4. Don't be shy!
This doesn’t apply only to new buildings – appraise existing buildings and if the ventilation space isn’t enough then improve it. It is generally cheap to do and the benefits will be immediate.
Never, ever, choose to use simple steel roof sheets in livestock housing. Steel has none of the required physical properties for livestock roofs and leads to increased condensation, temperature fluctuations and noise – all of which affect welfare and health. Always use fibre cement sheets for livestock building roofs.
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