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Guide to building a base for a garden building

Introduction

Assembling a garden shed/workshop/summerhouse may seem like an overwhelming task to a DIY novice. However if a level, sound and sturdy base is provided the rest should be simple. Making the base for a garden building is an easy task for a single person to complete. However we recommend two or more people are available to assemble the garden building.

Planning permission is normally not required for a prefabricated garden building. However, if you live in a conservation area, you may wish to check with your local council prior to construction.

Planning where the garden building should go

Consider the optimum site for your garden building in terms of:

Access to where the garden building is going to be assembled for the delivery team.
Access to all sides of the building once erected for applying wood treatments, maintenance etc.
Surrounding area conditions (Foliage, young trees that may grow in future, areas open to extreme elements etc.)
Natural light (a light area is best if the building is to be used as a workshop for example)
View from the assembled building (for summerhouses etc.)
Is an electrical supply going to be installed to the garden building and does it have any implications?

Types of Suitable Base

It is essential to provide a solid and level base. Attempting to assemble a garden building on an unlevel or soft surface will incur difficulties in squaring the building up when putting on the roof and doors will often not close properly. We recommend the following 5 types of base:

A Concrete Base
A Paving Slab Base
Tanalised Bearers
Eco Base
Portabase – A new concept in shed building, exclusive to Walton Garden Buildings - click here for details

Whichever method you deem the most suitable, we strongly recommend that your base be made to the same measurements as the floor of the garden building you are assembling. This allows the majority of rain to run off the walls and roof and soak-away instead of pooling on the base under the building and effectively creating dampness and rot problems.

If you are building your own log cabin, then please see our How to Build a Log Cabin page for details on building a base.

Concrete Base

Tools Required:

Pegs and string
Sand and gravel mix
Hardcore
Standard cement
Timber for base formwork
Tape measure
Spade
Sweeping brush
Cement mixer
Spot – mixing board
Wheel barrow
Tamp board
Spirit level.

For full instructions on how to build a concrete base for your garden building please see the below video for an easy step by step guide.

Step 1:

Be sure to position your garden building in an optimal space, allowing enough distance from hedges or fences for easy access to all sides. Using pegs and string to mark out the base the same area as the building's floor. Finally, measure diagonals to ensure the area is square.

Step 2:

A concrete base requires 3 inch (7.5 cm) of compacted hardcore underneath the 3 inch (7.5 cm) concrete layer. The base can be level with the ground or raised above it. If it is to be level excavate the top earth to 6 inch (15 cm) to allow for the hardcore layer and 3 inch (7.5 cm) thickness of concrete. Level the area with a rake and spade and remove the pegs.

Step 3:

Set up levelled formwork. This involves measuring, cutting and fitting timber, to the shape of the base in order to contain the concrete (as shown in the diagram). Check diagonals to ensure the formwork is square. And also ensure the formwork is level, as this will determine whether your base is 100% level. Next, spread a layer of well compacted hardcore and cover with a liberal amount of sand.

Step 4:

Next, mix concrete using one part cement to five parts ballast or use bags of dry-mixed concrete to which you just add water. Small amounts of water should be added at a time and mixed into the concrete mix to ensure excessive amounts are not added making the cement sloppy, as the concrete should be kept on the dry side.

Spread the concrete evenly and slightly proud of the formwork. This can be then levelled off with a long straight edge of timber resting on the formwork using a sawing motion slowly (as shown below) over the entire surface of the freshly laid concrete.

If wet weather is forecast, cover the concrete with polythene for 24-hours. In warm weather cover the base with damp sacks and sprinkle them with water over the 24-hour period, this will ensure the drying concrete will not shrink and crack.

The result is a smooth, sound, level base - the perfect foundation for the construction of a garden building or one of our wooden sheds. Allow 48 hours for the concrete to set prior to assembling your building.

Slab Base

Tools Required:

Pegs and string
Flat Face Paving Slabs
Sharp sand
Standard cement, rake
Tape measure
Spade
Rubber mallet
Sweeping brush
Spirit level

Step 1:

As mentioned above, decide where to position the shed in an optimal space. Allow enough distance from hedges or fences for easy access to all sides. Using pegs and string to mark out the base the same area as the building's floor. Finally, measure the diagonals to ensure the area is square.

Step 2:

Strip the topsoil and dig out to a depth of approx. 2.5 inch (7 cm) to accommodate the base. Level the area and remove the pegs.

Step 3:

Mix together one part cement to eight parts building sand for a dry sand and cement mix. Spread this evenly ensuring that the mix sits approx. 4 cm in depth. Now, rake this to a level.

Step 4:

Starting from one corner and working outward, lay the slabs by tapping down on the centre of each slab with a rubber mallet. Using a spirit level, ensure all the slabs are square, level and firmly butted together for a solid base.

Step 5:

The completed base should now be level and square. Do one final check with a long straight edge to check if the base is level from each corner, and also measure the diagonals to finally check the base is square. Brush off any excess dry sand/cement mix, which could hinder the leveling of the shed. The result is a smooth, sound, level base - the perfect foundation for the construction of a garden building.

Tanalised Bearers Base

Tools Required:

Pegs and string
Tape measure
Spade
Rubber mallet
Spirit level
Hardcore (crushed lime stone)
75mm x 75mm Tanalised Bearers

Step 1:

Step 2:

Strip the topsoil and dig out to a depth of approx. 3 inch (7.5 cm) to accommodate the base. Level the area and remove the pegs.

Step 3:

Fill the trench with hardcore and compact down as level as possible.

Step 4:

Lay the bearers on the hardcore, 16 inches (40cm) apart. The bearers should be laid at 90 degrees to the building's floor joists, i.e. if the floor joists run from side to side of the building then the bearers will need to run the length of the building. Check the orientation of the floor joists on your building as they do vary from building to building. Using the spirit level and rubber hammer, tap the bearers into the hardcore until they are perfectly level.

How to Build an EcoBase

Step 1:

Clear the area you’re going to use ensuring the ground is flat and there’s a slightly larger area needed than you require.

Step 2:

Cut the permeable membrane to size and lay flat.

Step 3:

Lay and interlock the grids and secure with 6 ecopins per grid spaced in alternate lugs. Take care to make sure that the feet of the grids are facing downwards and that there are no gaps between grids.

Step 4:

Cut the grids to the same size as the shed using a handsaw or alternatively, leave the EcoBase larger than the garden shed and fill with gravel. This will help to keep the timbers of the garden shed dry and free from splash back.