Shed foundations, like overall shed designs, range from temporary, utilitarian structures to heavy-duty, permanent fixtures. While building the most basic types of shed foundations requires few skills and relatively little labour, building the most permanent and complex types of foundations often requires excavation equipment, such as loaders and backhoes, and a crew of labourers. With an understanding of common types of foundations, you can design your shed's support system to suit the purpose of the structure.
Direct Contact Foundation
The term "direct contact foundation" refers to a wooden foundation that rests directly on the ground. Sitting on top of a direct contact foundation, the shed structure is raised above the ground's surface. Direct contact foundations consist of a wooden frame similar to a home's subfloor framing. Crossbeams, called joists, run between perimeter beams, called girders. Unfortunately, direct contact foundations often move as underlying soil settles. Additionally, whereas a direct contact foundation might last less than 20 years, masonry foundations often last hundreds of years. However, a direct contact foundation is the least expensive type of shed foundation, the easiest to build and capable of supporting heavy loads.
Post and Pier
Post and pier foundations consist of masonry columns, called piers, that support wooden posts. Builders often use precast, concrete piers or build custom piers from concrete blocks or poured concrete. Builders attach wooden posts to the top of piers with concrete anchors, brackets or straps and build a subfloor framework of girders and joists directly on top of the posts. Post and pier foundations apply not only to utility structures, such as sheds, but frequently appear among residential structures. Because post and pier foundations typically raise a shed's floor a foot or more above the ground, they are suitable for sloped building sites. However, post and pier sheds require ramps to get heavier equipment inside.
The standard foundation wall, also called a "stem" wall, is essentially a short, concrete block wall that sits directly on top of a below-ground, beamlike slab of concrete called a footing. The foundation wall runs along the shed's entire perimeter and supports wooden floor framing. The framework consists of perimeter beams, called girders, and crossbeams, called joists. To complete the subfloor structure, builders cover the floor framing with plywood and construct shed wall framing directly on top of the subfloor structure. Like a post and pier foundation, the foundation wall is suitable for sloped building sites. Unlike the post and pier foundation, the foundation wall forms an enclosed crawl space beneath the shed and bears structural loads not at specific points, but around the structure's entire perimeter.
Concrete Slab Foundation
Like an oversized stepping stone, a concrete slab is a thick, low-lying chunk of concrete, usually rectangular in shape. Depending on site conditions and building plans, concrete slabs range from 4- to more than 12-inches thick. To reduce cracking and heaving, builders pour slabs on top of a base of gravel and sand that settles evenly beneath the concrete, and place steel reinforcement mesh or bars within the slab's centre. Builders anchor wall framing directly to a slab's surface with concrete anchors or anchor bolts. Although slabs offer a long-lasting, durable foundation for sheds, constructing large slabs often requires exhausting physical labour and a crew of workers.