Local Regulations
Depending on the size of the gazebo being installed or constructed on your property, local building codes or homeowner association rules may dictate the use of a foundation. Some codes may not specifically mention gazebo, but any gazebo may be governed by the same construction and safety standards as an outdoor shed or deck. Investigate if any local guidelines or laws exist that pertain to your gazebo. In windy or hurricane-prone regions or where the ground freezes in winter, strict rules may require the gazebo to have some form of anchoring, steadfast foundation.
Types
Multiple materials and styles of foundations may be used under a gazebo structure. A level bed of crushed gravel, raised blocks, a wooden frame or a poured concrete or brick patio may all serve as a foundation. Regional climate may render some foundation types or materials obsolete or problematic. Local building codes usually take into consideration climate, material longevity and long-term safety issues if a foundation for an outdoor gazebo is mandated.
Advantages
A foundation under a gazebo provides many advantages. The foundation can elevate the gazebo to a desired height to provide an ideal focal point or viewing platform in your garden. The foundation also keeps the base of the gazebo off of the soil where moisture, micro-organisms and insects can be problematic. Keeping wood beams off of the soil and drained from rain and melting snow prolongs their life. In cold climates, a foundation that extends below the frost line prevents buckling and movement of the gazebo as the soil freezes and thaws over the years.
Caveats
Placing a gazebo directly on the lawn or bare soil is easiest. However, such a simple approach may not be financially, ethically or legally sound. If no building code governs the gazebo, placing the structure directly on the ground can lead to earlier rot of materials or sliding and tilting of the gazebo over time. In storm-prone regions, attaching a gazebo to a solid foundation can prevent wind gusts from toppling the structure or catapulting it onto a person or pet or crashing into a neighbor's property. Once installed, it takes additional money and resources to lift and repair or install a foundation after realizing there are structural or anchoring problems with the base of the gazebo.