Building a Shed Foundation: Concrete Slab vs Gravel Pad

Choosing the Right Shed Foundation: Concrete vs Gravel

Your shed foundation is the most important part of the entire structure. Get it wrong, and your shed will sink, tilt, and eventually fail. Get it right, and your shed will last decades. This guide compares the two best foundation options—concrete slab and gravel pad—so you can make the right choice for your situation.

Why Foundation Choice Matters

A proper foundation:

• Prevents settling and sinking
• Keeps the shed level and stable
• Protects the floor from moisture and rot
• Provides a solid base for heavy items
• Extends the life of your shed significantly

Skip the foundation or do it wrong, and you'll be rebuilding your shed in 5-10 years. Do it right, and it lasts 30+ years.

Option 1: Concrete Slab Foundation

A concrete slab is the premium choice—permanent, level, and maintenance-free.

Advantages:

• Permanent: Never needs replacement or maintenance
• Level: Perfectly flat surface that stays level forever
• Moisture protection: Keeps floor dry, preventing rot
• Heavy load capacity: Can support any weight
• Pest resistant: No gaps for rodents or insects
• Clean: Easy to sweep and keep clean

Disadvantages:

• Higher cost: Example cost: approximately $6-$10+ per square foot installed
• More complex: Requires forms, reinforcement, and proper finishing
• Permanent: Can't easily move the shed later
• Requires permits: Most areas require permits for concrete slabs

When to Choose Concrete:

• Permanent shed location
• Heavy items (workbenches, tools, equipment)
• Moisture-sensitive storage
• You want the best, longest-lasting solution
• Budget allows for premium option

Option 2: Gravel Pad Foundation

A gravel pad is the budget-friendly option that works well for many situations.

Advantages:

• Lower cost: Example cost: approximately $2-$4+ per square foot
• Easier installation: No forms, no concrete mixing
• Drainage: Excellent water drainage
• Flexible: Can adjust or move shed later
• No permits: Usually doesn't require permits

Disadvantages:

• Can settle: Requires proper compaction to prevent settling
• Weed growth: Weeds can grow through gravel
• Moisture: More moisture can reach the floor
• Maintenance: May need regrading over time
• Less stable: Not as solid as concrete for heavy loads

When to Choose Gravel:

• Budget is a primary concern
• Temporary or movable shed
• Light storage only
• Excellent natural drainage needed
• DIY project with limited experience

Concrete Slab: Complete Installation Guide

If you choose concrete, here's how to do it right:

Step 1: Excavation

Dig to a depth of 6-8 inches. The slab itself will be 4 inches thick, plus 2-4 inches of gravel base. For a 10x12 shed, that's approximately 1.5-2 cubic yards of excavation.

Step 2: Gravel Base

Fill with 4-6 inches of compacted gravel (crushed stone, not round pebbles). This provides drainage and a stable base. Compact thoroughly with a plate compactor or hand tamper.

Step 3: Forms

Build forms from 2x4s or 2x6s. Make them level and square. The forms should be the exact size of your shed floor.

Step 4: Reinforcement

Use wire mesh or rebar grid. Place it 2 inches from the bottom (use rebar chairs or small stones to elevate it). This prevents cracking.

Step 5: Pour Concrete

Order ready-mix concrete (approximately 1.5 cubic yards for a 10x12 shed, 4 inches thick). Pour, screed level, and finish with a trowel or broom.

Step 6: Curing

Cover with plastic and keep moist for 7 days. Don't build the shed on it for at least 7 days (28 days for full strength).

Example cost breakdown (for reference only): For a 10x12 (120 sqft) shed foundation: approximately $720-$1,200+ for materials and labor if DIY, or approximately $1,200-$2,000+ if professionally installed. Actual costs vary significantly.

Gravel Pad: Complete Installation Guide

If you choose gravel, here's the proper way to build it:

Step 1: Excavation

Dig to a depth of 6-8 inches. Make it 6-12 inches larger than your shed on all sides for stability.

Step 2: Base Layer

Fill with 4-6 inches of large gravel (2-4 inch stones). This is the foundation layer. Compact thoroughly.

Step 3: Top Layer

Add 2-3 inches of smaller gravel (3/4 inch crushed stone). This creates a smooth, level surface. Compact again.

Step 4: Leveling

Use a screed board or level to create a perfectly flat surface. This is critical—an uneven pad creates an uneven shed floor.

Step 5: Final Compaction

Compact the final layer thoroughly. The pad should be solid and stable—you shouldn't be able to push gravel around with your foot.

Example cost breakdown (for reference only): For a 10x12 (120 sqft) shed pad: approximately $240-$480+ for gravel and delivery. Actual costs vary.

Cost Comparison (Example Only)

Disclaimer: These are example costs for reference. Actual costs vary based on location, materials, site conditions, and project specifics.

For a 10x12 foot (120 square feet) shed foundation:

Concrete Slab:

• Excavation: approximately $200-$400+
• Gravel base: approximately $150-$300+
• Concrete (1.5 yards): approximately $350-$550+
• Reinforcement: approximately $100-$200+
• Forms and tools: approximately $50-$150+
• Example total: approximately $850-$1,600+ DIY, or approximately $1,200-$2,400+ professional

Gravel Pad:

• Excavation: approximately $100-$200+
• Gravel (approximately 3-4 cubic yards): approximately $150-$300+
• Delivery: approximately $50-$100+
• Compaction equipment rental: approximately $50-$100+
• Example total: approximately $350-$700+

Cost difference: Gravel pad is typically approximately 50-60% less expensive than concrete, but concrete lasts longer and requires no maintenance.

Which is Better? The Real Answer

It depends on your situation:

Choose concrete if:

• This is a permanent shed location
• You're storing heavy items or equipment
• You want zero maintenance
• Budget allows for the premium option
• You want the best long-term value

Choose gravel if:

• Budget is tight
• You might move the shed later
• Storage is light (lawn equipment, seasonal items)
• You need excellent drainage
• You want a simpler DIY project

Common Mistakes to Avoid

For concrete:

• Skipping the gravel base (concrete will crack)
• Not using reinforcement (will crack under load)
• Pouring too thin (4 inches minimum)
• Not leveling properly (shed will be crooked)
• Building shed too soon (wait 7 days minimum)

For gravel:

• Not compacting enough (will settle and sink)
• Using wrong gravel size (needs proper gradation)
• Not leveling the surface (shed floor will be uneven)
• Making pad too small (should extend beyond shed)
• Skipping the base layer (will settle over time)

Hybrid Option: Concrete Perimeter with Gravel Center

For larger sheds, consider a hybrid: concrete perimeter (footing) with gravel center. This provides the stability of concrete at the edges (where the walls sit) with the cost savings of gravel in the center.

Example cost: Approximately 30-40% less than full concrete, but more stable than gravel alone. Actual costs vary.

Maintenance Requirements

Concrete: Zero maintenance. It lasts forever with no upkeep.

Gravel: May need occasional regrading if settling occurs. Check level annually and add gravel if needed.

The Bottom Line

Concrete is the premium choice—permanent, maintenance-free, and the best long-term value. Gravel is the budget choice—works well for light storage and temporary locations. Both are valid options; choose based on your budget, permanence needs, and storage requirements.

For most permanent sheds with typical storage, concrete is worth the extra investment. It eliminates future problems and provides a solid foundation that lasts as long as the shed itself. For budget-conscious projects or temporary locations, a properly built gravel pad works well.

Whichever you choose, do it right. A poor foundation will cause problems for the life of your shed. Invest in proper preparation, materials, and installation—it pays off in the long run.

Need help with your shed foundation? Contact Local Concrete Contractor. We specialize in concrete slab foundations for sheds and can help you choose the right option for your project.