A worker uses a hand trowel to smooth wet concrete on a construction site.

Concrete Slabs & Foundations

Structural Bases for Garages and Additions

Concrete Slabs & Foundations in Seattle for homeowners building detached garages, sheds, or room additions

HOFFMAN CUSTOM CONCRETE pours concrete slabs and foundations for residential projects in Seattle that require a stable, level base for new structures. You may be adding a detached garage that needs a reinforced slab capable of supporting vehicle loads, or building a shed or workshop that requires a frost-resistant foundation. The work begins with excavation and site preparation, followed by formwork and reinforcement placed according to the structural requirements of the building above.


A garage slab is poured thicker than a standard patio and includes rebar positioned to resist cracking under the weight of vehicles and storage. The edges are formed to create a perimeter that ties into the framing, and the surface is finished level with a slight pitch toward the door opening to prevent water from pooling inside. For additions, the foundation may include footings that extend below the frost line, along with stem walls that support the floor framing and exterior walls.



If you are planning a garage, shed, or addition, contact HOFFMAN CUSTOM CONCRETE to review your building plans and schedule the foundation or slab work.

What Makes a Slab Structurally Sound

Your site is excavated to the depth required by the building design, and the soil is compacted to prevent settling. A gravel base is spread and leveled to provide drainage and a stable platform for the concrete. Rebar is tied in a grid pattern with spacing determined by the engineer's specifications or local building code, and the forms are braced to hold their position during the pour.



After the concrete is placed and leveled, you will have a flat, monolithic slab with no joints or seams where the structure rests. HOFFMAN CUSTOM CONCRETE finishes the surface with a wood float or steel trowel depending on whether the floor will be covered or left exposed. The slab cures for several days before framing can begin, and anchor bolts are set in the wet concrete to attach the bottom plate of the wall framing.


For foundations with footings, the work includes digging trenches below the frost line, placing rebar in the footings and stem walls, and pouring in stages to allow each section to cure before the next is placed. The finished foundation provides a level bearing surface for the floor system and transfers the building load into the soil without settling. The work does not include framing, waterproofing, or insulation, though the foundation is designed to accommodate those trades once the concrete has cured.

Common Questions About Slabs and Foundations

Homeowners often ask about thickness, reinforcement, and how the work fits into the overall construction schedule.


  • How thick does a garage slab need to be? A garage slab is typically poured at four to six inches thick depending on vehicle weight and soil conditions, with rebar spaced at 18 inches on center to resist cracking from repeated loading.

  • What is the difference between a slab and a foundation with footings? A slab is a single pour that serves as both the floor and the base, while a foundation with footings includes separate trenches poured below the frost line to support stem walls that the floor framing rests on.

  • How long before framing can start? The concrete must cure for at least seven days before framing loads are applied, though lighter work such as layout and anchor bolt installation can begin after 48 hours once the surface is firm.

  • Why are anchor bolts set during the pour in Seattle? Anchor bolts secure the bottom plate of the wall framing to the concrete, preventing the structure from shifting during wind or seismic events, and they must be placed while the concrete is still wet to achieve proper embedment.

  • What happens if the site has poor soil? The excavation is deepened and the subgrade is replaced with compacted gravel or engineered fill to provide a stable base, and the slab thickness or reinforcement may be increased based on a soils report.


HOFFMAN CUSTOM CONCRETE coordinates with builders and homeowners throughout Seattle to schedule foundation and slab work that aligns with construction timelines. Call to discuss your project requirements and receive a detailed estimate.