How to lay a base for your new garden building
To give your shed the longest life possible and ensure it is safe, providing a level, sound, sturdy base is essential. Building the base for a garden building is an easy task for a single person to complete and we would recommend 3 to 4 hours of labour will have your base ready for your new garden building or shed.
This guide takes you through the basics of laying your base, it is not a detailed instruction sheet and should be followed with common sense and safety in mind, however you should ensure your base is flat, level and square before you have a shed erected on your base and wear all necessary safety or protective clothing.
Planning permission is normally not required for a prefabricated garden building, however, if you live in a conservation area or the building could intrude on a neighbours garden, you may wish to check with neighbours or local council prior to construction.
Consider the optimum site for the your garden building in terms of:
- General access (for delivery of garden building, access to all sides for maintenance and applying wood treatments etc.)
- Surrounding area conditions (Foliage, young trees that may grow in future etc.)
- Natural light (a light area is best of the building is to be used as a workshop for example)
- View from the planned area (for summerhouses etc.)
- Do you intend to run an electrical supply to the building and does it give any implications?
It is crucial to provide a level and dry foundation. It is unfeasible, and potentially dangerous, to assemble a shed on an unsound base. For larger buildings (20ft+), especially where the shed is to be used as a workshop or garage, a full concrete base is best. However, generally paving bases are more than adequate for a garden shed, summer house or workshops.
The size of our shed floor/bases is approximately 1½ inches under the size of your building, so you can lay your base to the size of your new building if you wish, however we would recommend making the base up to 4 inches bigger if possible.
Fenton Portable buildings do not lay bases for any garden buildings, although we do offer additional bearers, base frames and a levelling-when-fitting service. Please contact our office for details on these services.
We do, however, have an independent base layer we can ask to contact you should you read this guide sheet and decide you need someone more qualified to lay your base! This base layer is not affiliated with Fenton Portable Buildings but has worked with us for many years and is also happy to quote you for other general building and garden work.
Slab Base Method
Pegs and string, Paving Slabs, Building sand, Standard cement, Rake, Tape measure, Spade, Rubber mallet, Sweeping brush
- As mentioned 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 2 inch (5 cm) larger than the area of the building on each side. Finally, a measure diagonal to ensure the area is square.
- 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.
- 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.
- 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.
- 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 levelling of the shed. The result is a smooth, sound, level base. The perfect foundation for the construction of a garden building.
Concrete Base Method
Pegs and string, Building sand, Standard cement, Timber for base frame work, Tape measure, Spade, Sweeping brush
- 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 2 inch (5 cm) larger than the area of the building on each side. Finally, measure diagonals to ensure the area is square.
- 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.
- Set up levelled formwork. This involves measuring, cutting and fitting timber, to the shape of the base in order to contain the concrete.
- Check diagonals to ensure the formwork is square. And also ensure the formwork is level, as this will determine whethery your base is 100% level. Next, spread a layer of well compacted hardcore and cover with a liberal amount of sand.
- 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.