A shed floor consists of a base and the decking over it. The right flooring can make a significant difference to the stability and longevity of the shed. Strength is important, but it's just the beginning of the story. Other considerations when selecting flooring for a utility shed include ventilation, water-resistance and, of course, cost. Choices are no longer limited to traditional flooring options such as a concrete slab. You can now find a range of options including recycled plastic bases and oriented-strand board.
A concrete base is one of the more traditional options for a utility shed. You will need to build a timber form, into which you place a layer of hardcore (pebbles, broken stones and rubble) with the concrete on top. Once the concrete has set, you have a sturdy, durable flat base. Concrete is a popular choice, but it has some drawbacks. Poorly laid concrete can break and crumble. Rain splashing back from a concrete base can cause wooden sheds to rot unless careful waterproofing is used.
A slab base is made with concrete paving slabs and cement. It has the advantages of being relatively quick to put down, sturdy and made of easily available and inexpensive materials. It's easy to adjust the level of the slabs so they lay flat. A slab base has similar drawbacks to a concrete base, including the possibility of cracking in adverse weather conditions.
Tanalised Bearers Base
This kind of base uses supports made of tanalised timber. Tanalised means preserved using high-pressure impregnation with a substance such as arsenic or copper. To make this base, put down a layer of crushed limestone hardcore, then lay the bearers on top at right angles to the joists of the utility shed. Tanalised bearer bases have the advantage of being inexpensive and easy to lay, but the results may not be as sturdy as concrete.
Eco Base is a recycled plastic material used to construct bases for sheds and greenhouses. It is moulded into the form of a grid. You cut the material to size using a hacksaw and fill the cells in the grid with pea gravel. Eco Base has the advantage of being lightweight, rot-proof and reusable. As a recently developed material, it doesn't have the track record of more traditional materials.
Timber Floor Boards
Timber floor boards are laid over the shed's base. They are usually tongued and grooved: a ridge along one side of each board slides into a groove along the side of the next. A timber floor has the advantage of being strong and durable. It is a bit more expensive than other options, however.
OSB and Plywood
OSB (oriented-strand board) and plywood are usually supplied in the form of square-cut boards. To make a floor from these materials as strong as possible, you should aim to support the edges where the boards join by nailing them over a joist. OSB and plywood are inexpensive and easy to install, but they can be flimsy compared with timber.
If your utility shed is installed on top of a concrete base, you can use this as the flooring. This avoids the need for building a separate floor, saving time and money. A concrete floor is also very strong if properly constructed. You can purchase concrete paint at most hardware stores if you'd like a more finished look, or consider more expensive options, like acid-staining the concrete.