Building a Shed Foundation

Building a Shed Foundation: The Monolithic Pour Method

A proper shed foundation prevents settling, frost heave, and rodent problems. The monolithic pour method—a 4-inch slab with thickened 12-inch edges—is the professional approach that solves all these issues in one pour. This guide covers exactly how to build it.

Why Monolithic Pour Works

The monolithic method combines the slab and thickened edge (footing) in one pour. This:

• Prevents frost heave (thickened edges go below frost line)
• Keeps rodents out (no gaps or joints)
• Creates a solid, stable base
• Is more cost-effective than separate footing and slab

Foundation Specifications

Slab thickness: 4 inches (standard for sheds)

Edge thickness: 12 inches (thickened edge/footing)

Edge width: 12 inches wide (around perimeter)

Concrete: 4000 PSI recommended (3000 PSI minimum)

Reinforcement: Wire mesh in slab, rebar in thickened edges

Step-by-Step Construction

Step 1: Excavation

Dig to a depth that accommodates:

• 4 inches for the slab
• 8 additional inches for the thickened edge (total 12 inches at edges)
• 4-6 inches of gravel base

Total depth: approximately 16-18 inches at the edges, 10-12 inches in the center.

Step 2: Gravel Base

Fill with 4-6 inches of compacted gravel. This provides drainage and a stable base. Compact thoroughly.

Step 3: Build Forms

Build forms for the outer perimeter. The forms will be 4 inches high in the center (for the slab) and 12 inches high at the edges (for the thickened edge).

Create a "step" in the forms: outer edge is 12 inches high, inner area is 4 inches high. This creates the monolithic thickened edge.

Step 4: Reinforcement

Wire mesh: Place in the 4-inch slab area

Rebar: Place in the 12-inch thickened edges (both horizontal and vertical)

Step 5: Pour Concrete

Pour concrete to fill both the slab area (4 inches) and the thickened edges (12 inches) in one continuous pour. This is the "monolithic" aspect—everything is one piece.

Step 6: Finish and Cure

Finish the surface, then cure properly (cover and keep moist for 7 days).

Why This Prevents Problems

Frost heave: The 12-inch thickened edges extend below the frost line, preventing the foundation from being lifted by freezing ground.

Rodents: The monolithic pour creates no gaps or joints where rodents can enter. The solid concrete base keeps them out.

Settling: The thickened edges provide extra support around the perimeter, preventing edge settling that can cause the shed to tilt.

The Bottom Line

The monolithic pour method—4-inch slab with 12-inch thickened edges—is the professional approach to shed foundations. It prevents frost heave, keeps rodents out, and provides a stable base in one efficient pour.

This method is more work than a simple flat slab, but it's worth it for a foundation that actually works and lasts. Follow these specifications, and your shed foundation will be solid and problem-free.

Need help with your shed foundation? Contact Local Concrete Contractor. We specialize in properly engineered foundations that prevent common problems.