How to build the best base for your garden building?

Whether you're planning to construct a garden shed, greenhouse, or a garden room, a solid foundation is crucial for ensuring the longevity and stability of your structure.

Here's a step-by-step guide to creating the best foundation for your garden building. 

Step 1: Planning and Design

Before you begin construction, careful planning is essential:

  1. Purpose and Size: Determine the purpose of your garden building and its dimensions.
  2. Location: Choose a site that is level, well-drained, and easily accessible. Consider walls, trees and boundaries before deciding on where to construct your garden base. If you are planning to add electricity or water you need to consider positioning your building close to a mains supply.  

Step 2: Choose the Type of Foundation

There are several types of foundations to consider, each with its own advantages:

  1. Concrete Slab: Provides a solid, permanent foundation that is ideal for heavy structures we would always recommend this for our Lugarde/ Woodpro buildings.
  2. Overlaid flagged base Our overlay flagged bases are made from paving slabs that are laid directly onto a prepared sub-base. This construction method provides a solid and durable foundation that can withstand the weight of your garden building and resist shifting or settling over time. Greenhouses can be completely flagged or perimeter flagged depending on your preference. 
  3. Timber Frame: A raised wooden frame; good for lightweight structures and easy to construct.
  4. Gravel Pad: A simple and cost-effective option for small sheds or greenhouses; provides good drainage.

Step 3: Prepare the Site

Proper site preparation is crucial for a stable foundation:

  1. Clear the Area: Remove any vegetation, rocks, and debris from the site.
  2. Level the Ground: Use a shovel and rake to level the ground as much as possible.
  3. Mark the Layout: Use stakes and string to outline the perimeter of the foundation.

Step 4: Construct the Foundation

Concrete Slab Foundation
  1. Excavate the Site: Dig out the area to a depth of about 6-8 inches.
  2. Add Sub Base: Spread a 4-inch layer of sub base and compact it.
  3. Install Formwork: Build a wooden frame (formwork) to hold the concrete in place.
  4. Pour Concrete: Mix and pour the concrete into the formwork, level it with a screed, and smooth the surface with a trowel.
  5. Cure the Concrete: Allow the concrete to cure for at least 48 hours before removing the formwork. We lways recommend at least 115mm of concrete for our garden rooms.
Overlaid flagged bases
  1. Mark Locations: Mark the locations for the base on your building's dimensions.
  2. Position the First Flagstone: Place the first flagstone in a corner or along the edge of the area.
  3. Level the Flagstone: Tap the flagstone gently with a rubber mallet to set it into the bedding layer. Use a spirit level to ensure it is level.
  4. Continue Laying Stones: Place the next flagstone, leaving a small gap (about 1/4 to 1/2 inch) for jointing material. Continue laying the stones, checking for level and adjusting as needed.
  5. Dry Jointing (for Sand Bedding): Sweep fine sand or kiln-dried sand into the joints using a broom. Compact the sand by sweeping until the joints are filled.
  6. Wet Jointing (for Mortar Bedding): Use a pointing trowel to fill the joints with mortar mix. Smooth the joints for a neat finish. 
Timber Frame Foundation
  1. Prepare the Site: Clear and level the ground as described.
  2. Lay Out Timber Frame: Cut treated timber to size and lay it out in the shape of the foundation.
  3. Secure the Frame: Connect the corners using metal brackets or screws.
  4. Add Gravel: Fill the inside of the frame with gravel for drainage and stability.
Gravel Pad Foundation
  1. Excavate the Site: Dig out the area to a depth of about 4-6 inches.
  2. Add Gravel: Fill the excavated area with gravel and level it.
  3. Compact the Gravel: Use a plate compactor or hand tamper to compact the gravel firmly.
Soft Soil Foundation

Greenhouses can be erected directly onto soft soil. We only recommend this for small greenhouses. If this is your chosen base you will need to purchase a soft soil support - this goes along the front to support the thresh.

Step 5: Ensure Proper Drainage

Proper drainage is essential to prevent water damage:

  1. Slope the Site: Ensure the site slopes away from the foundation to direct water away.
  2. Install Gutters and Downspouts: If applicable, install gutters and downspouts on your garden building to manage roof runoff.

Step 6: Final Checks

Before proceeding with building your garden structure, perform the following checks:

  1. Check for Level: Use a spirit level to ensure the foundation is perfectly level.
  2. Verify Measurements: Double-check all measurements to ensure accuracy.
  3. Inspect Stability: Ensure the foundation is stable and secure.


Building a strong foundation for your garden building is a crucial step that ensures the durability and stability of your structure. By following these detailed steps, you can create a solid base that will support your garden shed, greenhouse, or garden room for years to come. Happy building!

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