Building a detached garage is a complicated project that, if done yourself, requires a fair amount of expertise. Arguably the most important aspect of the construction is its foundation. Most commonly made from concrete, the foundation effectively transfers the weight of the structure to the earth below. There are a number of different methods that can be used, depending on the climate, soil quality and topographical conditions you have to work with. Consider the following options:
This type of foundation consists of a shallow, horizontally-oriented slab of concrete that is poured into a preset mold. The mold or frame is constructed from wood which will be later removed. The resulting slab is made to the exact dimensions of the garage.
Rubble Trench Foundation
This method uses a concrete slab atop a trench filled with stones or other rubble. The trench is dug at a slight grade to improve drainage, while the poured slab is steel reinforced and raised above the ground to provide clearance.
In cases where the underlayer of soil is poor or the garage will be built into a hillside or in a flood zone, a deeper slab foundation is necessary. The idea is that the load from the structure is transferred through the weaker soil layer onto the sturdier bedrock or clay.