What a shed base has to do
The base transfers every load into the ground while keeping the timber floor level, ventilated and away from persistent moisture. It must resist settlement, frost movement, erosion and local soft spots. It also sets the geometry for everything above: if the support is twisted, the wall frames rack, the door binds and roof planes become difficult to align.
Begin by removing vegetation and organic topsoil. Find firm material, understand how rain crosses the site and establish a finished level that will not create a dam against fences or buildings. The excavation depth and sub-base depend on soil and load; blindly copying a shallow online detail is risky on made ground, clay or a slope.
Paving slabs on a prepared bed
Paving slabs suit small and medium sheds where the ground is stable and access favours hand work. A compacted granular sub-base spreads load, while a controlled laying bed makes final levelling possible. Slabs can form a complete pad or support selected bearer lines, but isolated pieces dropped on soil will settle independently.
The advantages are familiar materials, modest wet trade and the possibility of lifting and correcting local areas. The disadvantages are the number of levels to control and the temptation to skimp on excavation. Provide a slight fall to the surrounding surface while keeping the actual bearer supports in one plane.
Concrete blocks or piers
Blocks concentrate support at designed points or lines and leave a useful ventilated void under the shed. They are practical on a gentle slope because levels can step, but every support must bear on adequate formation and be restrained from rocking. Hollow, lightweight or damaged blocks are not interchangeable with suitable dense units.
Set support positions from the bearer layout rather than whatever spacing looks convenient. End bearings, joints and heavily loaded zones need intentional support. Keep timber separated from masonry with an appropriate damp barrier and maintain enough access to inspect for decay, pests and washout.
Treated timber skids
Skids create a semi-portable foundation system: robust treated runners support the floor cassette and can sit on a drained granular bed or designed pads. They work well for smaller buildings that may need repositioning and for sites where a full slab is undesirable. The skid itself becomes a critical ground-near component.
Use treatment suitable for the actual hazard class and protect cut ends according to the supplier’s system. Good drainage is essential because preservatives extend service life but do not make timber immune to constant saturation. Anchor the building where wind exposure or use makes sliding or overturning credible.
A concrete slab
A slab offers a durable, continuous surface and can be the finished floor for a workshop. It spreads loads and makes wheeled equipment easy to move. It also commits the location, uses more embodied material and needs formwork, reinforcement or joints appropriate to the design. Poor levels and trapped water are difficult to correct later.
Decide whether timber walls sit directly on a raised kerb or whether the shed retains its own floor cassette above the slab. Direct fixing needs moisture separation, anchors and weather detailing at the perimeter. A slab top left flush with surrounding ground invites splashback and runoff into the wall line.
Match the base to the shed
For a 6×4 ft store on firm, level ground, prepared slabs or blocks are often proportionate. An 8×6 ft general-purpose shed benefits from continuous bearer lines and a well-compacted formation. A 10×8 ft or 12×8 ft workshop with heavy tools may justify a designed slab or a more substantial suspended base.
Before deciding, list ground type, slope, drainage, access, desired lifespan, floor finish, heaviest load and whether the shed may move. Price the complete system, including excavation, spoil removal, sub-base, delivery and labour. The cheapest visible component can require the most remedial work if preparation is omitted.
Set out and check before the frame arrives
Establish two perpendicular control lines and use equal diagonals to prove the rectangle, rather than following a fence that may wander. Mark the finished shed outline, roof overhang and door approach. Then mark every bearer or wall support so the foundation matches the actual load path. Recheck access around the cladding and enough room to lift panels safely.
When the supports are complete, use a long straightedge, laser or water level across the whole footprint. Check individual points, diagonals and intermediate lines; a perimeter can look level while the middle support is high. Record the readings and correct them with durable, fully supported materials rather than stacks of loose scraps. Finally, confirm drainage after a hose or rainfall test before covering the area with the floor cassette.
Maintain the space below the shed
A raised floor only stays durable if the void remains dry and open. Do not bank soil, mulch or stored materials against the cladding after construction. Keep vents and gaps clear of leaves, inspect gutter discharge and look for signs of settlement such as a changing door gap. Early adjustment is easier than rebuilding a distorted floor.
Where animals can enter, use durable mesh that does not block ventilation or create a debris shelf. Avoid sealing a damp void with decorative skirting. If the base includes timber skids or bearers near the ground, inspect end grain and support interfaces particularly carefully. Record any packing added later so movement can be monitored rather than repeatedly hidden.