Shed foundation blocks can look like an inexpensive way to support a backyard shed. Buy a few blocks, position them under the floor, and the building appears ready to go.
The missing question is whether that arrangement suits the shed and the ground beneath it.
Some manufacturers use block supports as part of their installation systems. Other providers recommend different foundations. The correct choice depends on the building’s support requirements, the site, and the complete installation details.
Before buying blocks, obtain a support layout for your exact shed. A photograph of another building is not enough to establish the block type, quantity, or spacing you need.
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Still selecting a shed plan? Explore My Shed Plans. Check whether the chosen design provides clear floor and foundation details before deciding on block supports.
What Are Shed Foundation Blocks?
The phrase can describe several different products and arrangements.
These should not be treated as interchangeable.
| Product or arrangement | What to clarify |
|---|---|
| Solid concrete blocks | Whether the product and its bearing arrangement suit the design |
| Precast deck blocks | What members they support and the manufacturer’s installation requirements |
| Hollow concrete masonry units | Whether they are specified for the particular structural arrangement |
| Concrete paving slabs | Whether they are suitable for the proposed support loads |
| Masonry foundation walls | The designed footing, wall, reinforcement, and connection details |
This article focuses on individual supports beneath a shed floor. A designed masonry foundation wall is a different construction system.
Avoid asking a supplier simply for “some shed blocks.” Take the relevant specifications with you.
Why Advice About Blocks Can Seem Contradictory
Different providers are describing different buildings and installation methods.
For example, Tuff Shed’s pre-installation guidance describes using concrete blocks and wood shims for leveling within its installation system. Foundation contractor Site Prep recommends against block bases and favors other approaches for the projects it discusses.
Those positions should not be combined into a generic instruction for every shed.
Ask your own provider:
- Does this shed permit individual block supports?
- Which components bear on those supports?
- What preparation is required beneath them?
- What limits apply to leveling?
- How will the building be anchored?
Use our shed foundation options guide if you are still choosing between support systems.
How Many Blocks Does a Shed Need?
There is no dependable answer based only on the advertised footprint.
The support layout depends on the floor framing, runners or beams, spans, loads, and ground conditions. A shed with one floor design may need a different arrangement from another shed of the same size.
For that reason, a generic statement such as “use nine blocks for a 10 × 12 shed” should not be treated as a construction specification.
Obtain a drawing showing:
- Each support location.
- The member resting on it.
- Required bearing details.
- Block type and orientation.
- Ground preparation.
- Permitted leveling method.
- Connections and anchoring.
Do Not Assume Corner Supports Are Enough
Four corners are easy to identify, but they do not define the complete floor support requirements.
Some members may need intermediate bearing. Others may be designed to span between specific supports.
Follow the floor design rather than choosing a convenient pattern.
Our upcoming shed floor framing guide will explain the relationship between floor members and their supports.
Ground Preparation Matters as Much as the Blocks
A strong block does not compensate for unsuitable ground underneath it.
Before selecting a block arrangement, assess the proposed location for slope, drainage, disturbed soil, and other conditions that may affect support.
The preparation specification should identify how each bearing area is formed.
Do not assume that placing blocks on the lawn provides the same result as preparing a suitable bearing surface.
For the preliminary checks, see how to prepare ground for a shed.
Investigate Wet or Soft Areas
If a proposed support location is soft, waterlogged, or filled with loose material, resolve that condition before installing the shed.
Adding another block on top does not improve the underlying ground.
Where conditions are uncertain, obtain an assessment from someone qualified to recommend the preparation or foundation arrangement.
Can You Use Blocks on a Sloping Site?
Possibly within a suitable designed or manufacturer-approved system, but a slope needs more thought than raising one corner.
Measure the difference in ground level across the footprint. Give those measurements to the shed provider or foundation professional.
Ask whether the proposed arrangement is appropriate and what leveling limits apply.
Avoid improvising tall stacks to make up a substantial height difference. If the site requires significant elevation changes, a different support approach may be more suitable.
Our shed pier foundation guide covers an alternative to discuss for projects needing designed individual supports.
What About Frost and Seasonal Movement?
Surface supports need to be assessed for the local ground and climate.
Do not assume that a concrete block sitting near the surface provides the same foundation behavior as a designed footing.
Ask whether your proposed system is appropriate for local conditions and whether additional measures are required.
This is also a question for the applicable local building office. Using blocks does not, by itself, settle whether the project meets local requirements.
Our shed permit guide provides a checklist for that conversation.
Leveling and Shims: Follow the Exact System
Leveling details should be specified rather than improvised.
Where a provider permits shims, obtain its requirements for material, placement, support, and maximum adjustment. Do not generalize from another manufacturer’s installation method.
Loose scraps, broken paving pieces, and miscellaneous wedges are not a substitute for a defined detail.
Before loading the shed, have the support arrangement checked against the drawings or installation instructions.
Want to understand the floor support before purchasing materials? Take a look at My Shed Plans. Review the foundation drawings for your preferred design and clarify any missing block or bearing details.
Blocks Do Not Automatically Anchor the Shed
Holding a building above the ground and restraining it against movement are different functions.
A shed resting on blocks still needs the anchoring arrangement required by its design and applicable conditions.
Do not assume the weight of the shed, the blocks, or the stored equipment provides the required restraint.
Check how the connections work through the building and into the specified anchoring system.
Our upcoming guide to how to anchor a shed explains the information to obtain before installation.
Plan the Height Beneath the Doorway
Block supports can raise the finished floor above the surrounding ground.
Before accepting the final elevation, consider how you will move equipment through the entrance.
Check:
- Door threshold height.
- Space for a suitable ramp or step.
- The approach route.
- Door swing clearance.
- Access for maintenance beneath or around the building.
If you need a ramp, plan it with the entrance. Do not wait until the shed is loaded to discover that the approach is awkward.
The layout exercises in what size shed do I need? can help you picture daily use.
Compare the Complete Cost
The purchase price of the blocks is only one part of the foundation cost.
Include any required:
- Excavation and ground preparation.
- Base material.
- Delivery.
- Approved leveling components.
- Anchors and connections.
- Labor and equipment.
- Entrance ramp or step.
- Site cleanup.
If you are comparing blocks with a prepared pad or slab, compare complete suitable systems.
Our guides to a gravel shed foundation and a concrete shed foundation explain the questions involved.
Add the selected arrangement to your shed-building budget.
A low materials price is not a useful saving if the arrangement needs correction later.
A Practical Checklist Before Buying Blocks
Make sure you have answers to these questions:
- Is this support method permitted for the exact shed?
- Do I have a dimensioned support layout?
- Are the block product and orientation specified?
- Is the preparation beneath each support defined?
- Have slope and ground conditions been assessed?
- Is the leveling method clear?
- Is anchoring included in the plan?
- Does the entrance height work for my equipment?
- Have applicable local requirements been checked?
- Who will verify the installation before the shed is loaded?
Keep these details with the shed drawings and materials list.
What If an Existing Shed on Blocks Looks Uneven?
An uneven floor, changing door alignment, or visibly displaced supports deserves investigation.
Those signs do not establish the cause by themselves. The problem may involve the ground, support arrangement, floor, or another part of the building.
Do not crawl beneath or attempt to jack up an unstable shed using improvised equipment.
Have the support system assessed before attempting corrections. The remedy may require more than adding a shim.
If the shed came from a supplier, contact it with photographs and installation details.
Frequently Asked Questions
Can I put a small shed on concrete blocks?
Possibly, if the shed design permits it and the site, preparation, support layout, and anchoring are suitable. Small size alone does not establish suitability.
Are solid blocks better than hollow blocks?
They are different products with different applications. Use the specified support product rather than choosing by appearance. Hollow masonry units should not be improvised as interchangeable leveling blocks.
Can I use paving slabs instead of foundation blocks?
Only if the proposed product and arrangement are suitable for the design. A paving product should not automatically be treated as a structural support.
How far apart should shed foundation blocks be?
Use the spacing shown in the floor and foundation design. It depends on the members and loads being supported.
Can I stack blocks to level a shed?
Do not improvise a stack. Obtain the permitted arrangement and leveling limits from the responsible designer or manufacturer.
Do I still need gravel beneath the blocks?
The preparation specification determines what is required beneath each support. A general layer of gravel is not a substitute for those details.
Are blocks cheaper than a gravel pad?
They may have a lower initial product cost, but compare ground preparation, installation, anchoring, and access requirements before deciding.
Choose the Support Arrangement Before the Blocks
The right starting point is a supported shed design—not a shopping cart of inexpensive blocks.
Confirm the layout, ground preparation, leveling method, and anchoring. If those details are unclear, resolve them before construction or compare another suitable foundation.
Visit Beginner Shed Guide for more help planning the project.
Ready to review a design and its support requirements? Explore My Shed Plans, check the available samples, and clarify the foundation details for your chosen shed.
Resources
- Tuff Shed: Pre-Installation Guide — Manufacturer-specific information about site preparation and leveling.
- Site Prep: Shed Foundation Blocks — A foundation contractor’s discussion of concerns with block-supported sheds.
- Site Prep: Shed Footings — Background distinguishing surface blocks from other footing arrangements.
- Your selected shed drawings and support-product instructions — Confirm the actual layout, preparation, and installation requirements.
Affiliate disclosure: We may earn a commission from purchases made through affiliate links on this page, at no additional cost to you.
Building disclaimer: This article provides general planning information, not block spacing, bearing capacities, or a site-specific foundation design. Follow the selected shed system, applicable local requirements, and manufacturers’ instructions. Obtain qualified help for unstable structures or uncertain ground conditions.