The orientation of the greenhouse is typically north-south. A lot of emphasis internationally is placed on orientation to maximise light interception in the greenhouse. This is not such an issue in Australia because our light levels are much higher.
Shadows cast by gutters, trusses and equipment in the roof of the greenhouse can lead to uneven light conditions in the crop. As the sun moves from the east to the west during the day, the shadows of the greenhouse structure will also move. An east-west alignment creates structural shadows in the same part of the crop through the day which can affect crop productivity and plant health in this area. Subsequently, to minimise shading effects, greenhouses are generally oriented north-south.
In southern areas of Australia, an east-west orientation may result in slightly more light transmission, but the need for cooling and ventilation is a more important factor under Australian conditions. As you go further north, there is even less difference in light transmission which ever way a greenhouse is oriented. Again, cooling and ventilation and therefore the direction of prevailing winds should be the primary consideration in orienting a structure.
Crop rows are also typically aligned north-south to minimise shading within the crop. In most areas, vents will be on the east and west. The direction of prevailing winds should be taken into consideration, with structures oriented to take advantage of cooling summer breezes.
Where fans are used for forced ventilation, they should be positioned to minimise any likely impact on neighbours.
When siting a greenhouse, you also need to take into consideration the shading effect of vegetative screens and windbreaks. Locating greenhouses against a tree line will result in lower yields because of reduced light levels. Greenhouse covering materials near trees will also become quite dirty, further reducing light transmission.
When siting a greenhouse;