Why a Proper Base Is Important
All garden buildings must be assembled on a strong, flat, and level base made from a durable material.
If the base is uneven or unsuitable, the building can be difficult to assemble and may deteriorate over time. Common problems include:
Doors dropping out of alignment and becoming hard to open or close
Water leaks caused by poor positioning or movement
Building your garden structure on an incorrect base may also invalidate the product guarantee, so it’s important to get this right from the start.
Choosing the Right Location for Your Shed Base
Before building your base, take some time to decide on the best position in your garden.
Avoid placing the base too close to walls or fences, as the roof may overhang slightly.
Keep clear of trees and large bushes. Overhanging branches can damage the roof, especially as they grow. Trim any nearby branches before assembly and check them regularly afterwards to prevent wear to the roofing felt.
Think about access:
Leave enough space around all sides of the building for maintenance, such as applying wood treatments or preservatives.
Consider how easy it will be to move large or heavy items to and from the building.
Consider light and views, especially for summer houses or log cabins where you may spend time relaxing.
Plan for services if needed. If you intend to add electricity or water, think about the distance to the mains supply and the most practical route.
How to Build a Shed Base
For the best results, you may wish to hire a qualified local builder or handyman. However, if you are confident with basic DIY, building your own base is a manageable project.
This guide will walk you through preparing and constructing a suitable base using the material of your choice.
Important:
We strongly recommend making the base slightly larger than the building itself — allow approximately 30–40mm extra on each side. This helps with positioning and ensures proper support.
Concrete Base Method
This method is strongly recommended for larger garden buildings.
Clear the area
Remove all grass, plants, and debris from the area where the base will be built.Mark out the base
Use pegs and string to outline the base. Measure the diagonals from corner to corner — if both measurements are the same, the base is square.Dig the ground
Excavate the marked area to a depth of about 6 inches (150mm).Add the foundation layer
Fill the excavated area with about 3 inches (75mm) of hardcore, scalpings, or broken brick. Compact it firmly to create a solid base.
If needed, add a thin layer of compacted sand to level the surface. Use a rake to help level it. Once complete, remove the pegs and string.Install the shuttering
Cut and fit timber rails or steel shuttering around the edges to form the shape of the base (as shown in the diagram).
Use a tape measure, spirit level, and square to ensure the shuttering is perfectly level and square.
Mix and pour the concrete
Pour approximately 3 inches (75mm) of concrete into the shuttering.
You can either:Use ready-mixed concrete, adding small amounts of water, or
Mix your own using 1 part cement to 5 parts all-in ballast, plus water
Tip: Do not make the concrete too wet, as this will weaken it. All-in ballast is commonly sold in 40kg bags (about 1¼ bags makes 1 cubic foot of concrete).
Level and smooth the concrete
Spread the concrete evenly, making sure it reaches all corners and edges.
Add it in layers and compact each layer before adding the next.
Once full, level it with the top of the shuttering and smooth the surface using a wooden or plastic float.Let the concrete cure
Cover the concrete with sheets and allow it to dry naturally.
In warm or dry weather, lightly spray it with water to prevent it from drying too quickly.Ready to build
Once the concrete is firm and fully dry, the base is ready for assembling your garden building.
Paving Slab Method
Clear the area
Remove all grass, plants, and debris from the area where you plan to build your base.Mark out the base
Use pegs and string to outline the size of the base.
Measure from one corner to the opposite corner, then repeat for the other diagonal. If both measurements are the same, the area is square.Dig the ground
Excavate the marked area to a depth of about 2.5 inches (63.5mm).
Once dug out, remove the pegs and string.Prepare the bedding layer
Mix 1 part cement to 8 parts building sand to create a dry sand-and-cement mix.
Spread this mix evenly to a depth of around 1.5 inches (40mm).
Level the surface using a rake and check it with a spirit level.Lay the paving slabs
Starting from one corner, lay the paving slabs onto the mix.
Gently tap each slab down with a rubber mallet.
Make sure the slabs sit slightly higher than the surrounding ground to help rainwater drain away.Check alignment and level
Use a spirit level to ensure all slabs are level, square, and tightly butted together.Finish up
Brush away any excess sand and cement mix.
Your base is now ready for assembling your garden building.
Timber Bearers Method
Clear the area
Remove all grass, plants, and debris from the area where you plan to build your base.Mark out the base
Use pegs and string to outline the size of the base.
Measure from one corner to the opposite corner, then repeat for the other diagonal. If both measurements are the same, the base is square.Excavate the ground
Dig out the marked area to a depth of about 2 inches (50mm).
Once excavated, remove the pegs and string.Add the sub-base layer
Fill the area with approximately 1.5 inches (40mm) of gravel or compacted soil.
Level the surface using a rake and check it with a spirit level.Lay the floor bearers
Place either concrete floor bearers or pressure-treated (tanalised) timber bearers on top of the gravel or soil.
Space the bearers evenly at intervals of 400–600mm.
Make sure they run perpendicular to the floor joists already built into your garden building.Check everything is level
Use a spirit level to ensure all bearers are level with each other.
If needed, gently tap them into place using a rubber mallet.
How Many Floor Bearers Do I Need?
The number of bearers required depends on the size and design of your shed.
Most wooden sheds come with bearers already attached to the underside of the floor, running along the length of the building.
However, some models (such as 10x8 and 12x8 buildings with 28x44mm framing, and many TigerFlex sheds and summerhouses) have bearers running across the width instead.
Please check your model before planning additional bearers.
As a general guide:
6x4 garden building – at least 4 bearers, each 1150mm (4ft) long
7x5 garden building – at least 4 bearers, each 1450mm (5ft) long
8x6 garden building – at least 5 bearers, each 1750mm (6ft) long