4 steps to assess your dairy building’s ventilation

Well-designed and ventilated buildings are key to good animal performance. 

Buildings don’t have to be brand-new or cost a fortune to meet the right standards.

Small tweaks can be made to existing buildings to make them fit-for-purpose. 

Below researcher and animal health specialist Jamie Robertson walks Farmers Weekly through his protocol for inspecting dairy buildings for ventilation and points our simple steps producers can take to fix common issues.

1. Look at the big picture

Where does the building sit on your farm? The direction openings face and the proximity of any other structures influence the entire building environment.

Determine North, East, South and West directions in relation to barn openings. This is crucial to managing moisture, delivering fresh air, controlling air speed and maintaining a stable temperature.

See also: Step-by-step guide to planning dairy buildings

2. Watch the cattle, they’ll tell you what’s going on

If the cows could talk, they’d let us know every single thing that is wrong – but they can’t – so we must pay close attention to their behaviour and physical condition to understand the entire story.

Walk into the building quietly, but let your presence be known. Calm and relaxed cows are happy cows.

Cows that get up quickly and immediately move away are likely to be stressed and agitated, which may be due to a building issue.

Pay attention to building location and consider how daily and seasonal weather changes may impact when it’s hot, cold and windy – there is a strong relationship between cow position and the barn environment.

Are they evenly spaced out and comfortable? Or are they escaping or looking for drafts by huddling in bunches in one area of the building?

3. Rethink solid walls

We know the primary wind direction in Britain will be coming from the south-west, frequently resulting in the south-west wall of a building being solid to prevent rain coming in.

However, this also means free fresh air isn’t being delivered effectively to the building for half of the year.

For adequate airflow, determine inlet/outlet areas. For example, if a dairy building is 30m long, 20m wide, and contains 100 cows, then it needs a minimum of 10 sq m of hole space to get adequate airflow.

For simple and accurate design, access the AHDB Buildings Guide online.

How to fix it

  • If your roof cladding overlaps the wall beneath it, you can put in a 0.5m gap which will let air in above the cattle but keep rain out. 
  • Remove the solid wall above animal height and replace it with Yorkshire board on gable ends, an automatic curtain, or spaceboard on sidewalls.


  • If there are no other options, rough it and use a chainsaw to cut holes in the side of your building – understand this isn’t going to stop rain coming in.

4. Put a hole in the roof

When wind speed drops or where a building is less exposed, we need a hole in the roof.

Basic science tells us hot air rises and if there are no holes in the roof for air to escape, then the barn will become stuffy and humid and become a prime breeding ground for bugs.

The average 650kg Holstein cow will produce 10 litres of moisture per day through respiration and another 50 litres of moisture per day from urine and faeces.

A rough assessment says it takes 0.1 sq m of open roof space per cow to remove that moisture.

Say you have 200 cows, that means you need 20 sq m opened in your roof for adequate ventilation.

How to fix it

  • One option is to install protected open ridges along the ridge, which will keep rain out while allowing warm, stale air to flow outside.

Roof with protected ridge

  • You can also install upstands along an open ridge, which will restrict the amount of rain ingress and massively improve air extraction.
  • Roof openings are essential to adequate ventilation, so even if it means you are pulling ridges off your roof to get air moving, it is best to do something rather than nothing.

The stack effect

Maintaining adequate ventilation really comes down to two things: managing wind impact and the physics of the air inlet/outlet cycle.

As cows breathe out warm air, which may contain bacteria and viruses, it rises to the top of the building in the absence of wind.

It’s important to note that the average 650kg Holstein respires 10 litres of moisture per day, quickly turning a barn into a stagnant, humid environment without an outlet. Air inlets are also essential to support air movement in the absence of wind.

How good design can affect livestock performance

Recently, Marley Eternit produced the “Livestock building design and material guide for natural ventilation,” a full-colour brochure for beef, dairy, pig and youngstock housing. The content and illustrations are based on leading research and expert advice.

“It’s important that producers look at the entire building system when undergoing refurbishments and erecting a new build,” says Stuart Daniell of UK roof systems manufacturer Marley Eternit.

“Buildings will have a long-term impact on a business, so invest in materials and designs that will make it a profitable one.”

To download the ventilation guide, go to www.marleyeternit.co.uk/agri-ventilation-e-book.