What Kind of Underpinning Is Available for a Shed?

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Sheds offer a quiet and separate area away from the home for storage of farming and gardening equipment. Homeowners have many shed-building options, from choosing the overall dimensional shape to window placement.

However, before a shed becomes a permanent structure on the property, the ground must be prepared with underpinning. The typically small size of a shed gives the homeowner many material options for choosing an underpinning type.

Underpinning Function

Underpinning is a form of building foundation. The Earth's surface constantly shifts, such as when the ground defrosts after a cold, wintry period. The ground movement compromises a building's structural integrity by warping the shape, creating weak points. An underpinning layer on the ground creates a buffer between the shifting ground and the structure built upon it, protecting the building's shape and overall strength.

Shed Underpinning Types

A large shed, rivalling the size of a small barn, would require a poured concrete foundation, especially if the shed housed small farm tractors. However, a small, basic shed does not require a complicated underpinning. In fact, sheds smaller than 100 to 120 square feet do not require a building permit. Underpinning for these cosy structures can be a level, gravel covered surface with 6-by-6 foot treated lumber planks on top. Additionally, the homeowner can use concrete blocks or piers on top of gravel for a different underpinning solution.

Underpinning as a Repair Solution

Underpinning is also used as a form of foundation repair. Soil composition varies from region to region. However, clay soils are prone to drying out during long drought periods, causing the ground to crack and contract from lost moisture. Specifically, sheds built above clay soil can be adversely affected by the shifting ground movement, even with a properly built underpinning foundation. Typically, a repair contractor can dig a hole underneath the shed and fill it with concrete for an emergency underpinning solution. This concrete pier shores up the structure and protects it from further ground movement.

Additions to Underpinning

Each shed has a specific use in the mind of the homeowner. Some sheds are strictly for garden tool storage, while other sheds may be a gardening workplace. A vapour retarder installed under the floor helps insulate the shed if the homeowner would like to keep the shed heated during cold days. The vapour retarder is a thin membrane placed under the floor, as well as covering the walls and ceiling. It stops small drafts from entering the shed through gaps in the shed's structure.