Direct sun on a building's surface generates significant levels of heat. Shading can reduce 90% of this heat load. A variety of techniques are available to achieve this. Passive deign involves taking into account the buildings location, orientation and the times of year to input shading techniques that are able to reduce the summer heat gain. In Adelaide, a good rule of thumb for north facing windows is the 45% rule. The eave on a north facing wall to be 45% of the height of the sill to the bottom of the eaves.