Without getting caught up in discussions about climate change or changing weather patterns, the reality is that temperatures over the winter months have been higher than normal in recent years. This is leading to reports of greater health issues in cattle housed in sheds with poor ventilation and is also linked in such sheds to animal performance falling well below targets.

A good air flow in sheds is vital for several reasons. A sufficient supply of fresh air will remove gases, bacteria and odours from the atmosphere and also help to regulate an animal’s temperature by removing heat and moisture that they generate. This in turn will keep sheds dry, cooler and cut down on the chances of an environment establishing that bacteria or viruses will prosper in.

The tell-tale signs of poor ventilation are well documented – cobwebs and dust building up on the inner side of sheeting, timbers turning a dark black colour, rust developing quickly on sheeting, excessive condensation and a smell of stale air or ammonia when you enter a shed. Smoke bombs can be used to see what is happening with the air inside a shed.

Overstocking of sheds can also be an underlying factor so it is important when assessing ventilation to also ask yourself the question whether there are more animals present than the shed was originally designed to accommodate.

Improving ventilation

The type of ventilation present in over 99% of livestock sheds on the island of Ireland is natural ventilation, whereby fresh air is drawn into the shed replacing warm air which is naturally rising and exiting the building.

Problems occur where the size of the air inlets or outlets are not sufficient to regulate the flow of fresh air or support the stack effect, as detailed in Figure 1.

Figure 1: the stack effect

Some practical methods of addressing inadequate air flow are detailed in this article. But before delving into them, it is also wise to ask yourself if anything has changed on the site over time which has had a negative effect on ventilation. A regular occurrence is a line of trees or a shelter belt being planted to provide some shelter, but over time not being maintained and having the net result of stifling air flow.

Photos 1 to 3: replacing sheeting

It is common for fully enclosed back-to-back type sheds to be erected with vented sheeting or boarding along the eaves and solid sheeting on the gable ends. Vented sheeting generally works satisfactorily along the side of the shed which is most exposed to the prevailing wind, but can be poor in facilitating air flow into a shed on a sheltered side.

Photo 1: Spaced boarding installed on the gable end of the shed to improve the inlet air capacity.

The most common method of rectifying this is to replace the vented sheeting with spaced boarding or Yorkshire boarding. Spaced boarding works well in opening up the shed to greater air flow, but can let more rain pass through where exposed to the prevailing wind.

Yorkshire boarding (detailed in Figure 2) is a better bet here, as it will prevent rain from entering the shed.

Figure 2: Yorkshire boarding.

In some sheds which have become sheltered by the erection of another shed, a solution regularly seen is replacing a section of the eaves sheeting such as in one bay, for example, with a wind breaker to open the area up.

Where venting sheeting has been used in new builds, more farmers are opting to extend its use to gable areas, while the new regulations which request an unobstructed air inlet just under the eaves (photo 2) is also helping to improve air flow.

Picture 2: new regulations advise leaving an unobstructed opening under the eaves.

Photo 3 is an example of work carried out in Teagasc Grange, whereby the top section or top half of solid sheeted sliding doors is replaced with vented sheeting or a wind breaker.

This improves air flow, but prevents draughts at ground level.

Photo 3: The solid sheeting on the top section of this sliding door was replaced with vented sheeting.

Leaving doors open can work well in aiding ventilation and provide extra inlet or outlet capacity on calm days, but, as mentioned above, it is not a long-term solution, as it generally causes draughts.

Photo 4: altering air inlets

The alteration in photo 4 first came to light almost a decade ago on the farm of Marty Lenehan, a Teagasc/Irish Farmers Journal BETTER Farm programme participant from Co Sligo.

Photo 4: This section of vented sheeting was fastened together and joined to the shed with hinges allowing it to be opened on calm days and closed on windy days.

There was an inadequate flow of air into the shed on calm days, but as the shed was in an exposed area, it was not possible to make alterations that would leave the shed overly exposed.

The solution was to fix the vented sheeting together in a section which was secured to the shed by hinges, allowing the section to be opened and closed. Other similar solutions include slanting some sheets out from the shed at wall level to allow more air to enter the shed.

In old sheds that were constructed with a low height at the eaves and a high solid wall, lowering of the wall has proved beneficial.

Photo 5: raising the ridge cap

Photo 5: The height of the ridge cap and width of the canopy will have a direct effect on the flow of stale air out of the shed.

In many sheds, the ridge cap is either of an inadequate size or too close to the roof of the shed and limiting the flow of air. Some farmers not concerned with rainfall entering the shed and falling on the passageway have experimented with removing the ridge cap sheeting altogether where the opening is quite small, while others have successfully improved ventilation by raising the height of the ridge cap over the shed. In the latter case, the width of the ridge cap may need to be increased, as, if it was constructed to just about cover the canopy opening, it can also let in rainfall, which may not be a runner in straw-bedded sheds.

Photo 6: raising sheets

The ventilation in many old round-roof sheds or aged A-framed roofs that were not originally erected to hold livestock can be particularly poor. While not a straightforward job, raising one or two sheets or lines of sheeting by 100mm to 150mm and providing an overlap at each side (again 100mm to 150mm) can work successfully in sheds which are being altered to accommodate livestock.

Photo 6: ventilation can be improved in old round roofed sheds not originally designed for housing livestock by raising sections of sheeting.

Remember, safety is paramount when working on older sheds and it is vital to take the necessary precautions. Where sheeting on the entire roof is being replaced, then spaced sheeting will work excellently in improving the shed’s outlet air capacity.

Photo 7: altering the roof height

Ventilation will also be influenced by the pitch of the roof and the difference in height between inlets and outlets. Photo 7 is also one taken around a decade ago on Lisbeg Farm in Co Galway. There were significant ongoing issues with ventilation in one of the main finishing sheds.

Photo 7: This was a major job to undertake but it transformed ventilation in the shed.

The solution in this case was to raise one side of an A-shaped roof by adding three lengths of an RSJ as shown to raise and support the roof. The opening was extended to about one metre in height, while the roof was also extended to avoid an excessive opening being formed and significant volumes of rainfall entering the shed.

In short

  • Rising temperatures are increasing the need for good ventilation in sheds.
  • Vented sheeting on sheltered sides may not facilitate good air flow - Yorkshire boarding can be used here.
  • New building specifications advise an unobstructed air inlet just under the eaves.
  • The ridge cap height is a key factor in ensuring there is enough air flow.
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    Watch: Lisbeg Farms' journey to efficiently finishing 1,500 cattle