To ensure naturally ventilated free stall barns remain serviceable for years, the following construction ideas and methods may be used.
The ideal solution is a 20° to 25° roof pitch. Lower pitches may slow down air movement along the underside of the roof, trapping moist air and generating condensation. Pitches that are too high, on the other hand, may cause air flow in this area to speed up, causing poor distribution of fresh air at cow level during colder weather.
The presence of continuous open ridges allows warm, moist air to be drawn out of the building as wind blows across the ridges. Fresh, cool and dry air is simultaneously drawn in through side wall openings.
Ideally trusses should be quality galvanised steel or hot dipped gal. Bird proofed is better. The harder it is for birds to nest in the roof the better.
Ridge Caps/ Upstands
When a free stall barn is populated fully, only a minimal amount of rain or snow will come in through open ridges of the correct size. In wide barns (15m plus), ridge caps are typically not recommended, as they may obstruct the outlet of air provided by the ridge. They may even increase entry of precipitation if it happens to blow parallel with the ridge.
An upstand, on the other hand, will deflect rain and will not hinder air flow if installed on a ridge. A rain gutter below the ridge to intercept rain or snow is another viable alternative.
Properly designed vented ridge caps can be used in barns up to 12m width with a central feed aisle, to prevent feed becoming wet. The cap must, however be installed correctly to prevent air flow from being blocked.
Side walls must be between 3.6m and 4m high to allow for maximum ventilation during summer. A 4m side wall is essential if the barn is sheltered by other buildings, other obstructions or tall crops. 4.5m’ or higher will not have noticeable impact on ventilation.
Perching or roosting birds foul feed, animals and parts of the building. They also peck at and destroy insulation materials. While it is difficult to control them, it is possible to minimize perching opportunities, especially over feed aisles. Bird netting will also assist in keeping them down.
Openings on side and end walls should be adjustable and completely removable to allow for varying weather conditions. Roll up doors, sliding doors, and removable curtains are recommended.
Minimum Insulation/ Roof Overhang
A quality Insulation product like glareshield from the Air-cell range product range that is a water resistant material could be used for best effect. A minimum of 900mm eave or roof overhang should be used to minimize entry of rain, snow and sun.