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Concrete Slabs & Foundations in Denver, CO

Quick answer

Shed and equipment pads around Denver are usually reinforced slabs over compacted gravel. Garages and workshops need thicker slabs and footings, often built as floating slabs on swelling soil. Additions need a permit, inspections and usually a soils report and engineered foundation design. Colorado has no statewide contractor license, so check local licensing, and contact Colorado 811 before digging.

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Sheds, detached garages, workshops, hot tubs and room additions all need a solid base. For small structures, that's usually a simple slab. For anything attached to the house or built as living space, it means foundation work that must meet the building code your city or county has adopted, pass inspection, and account for the swelling soils found across much of the Denver metro.

Common slab and foundation projects

  • Pads for storage sheds, playhouses and garden buildings
  • Slabs for detached garages, workshops and carports, including garages off an alley
  • Pads for hot tubs, generators and HVAC equipment
  • Footings and foundations for additions, sunrooms and covered porches

Small structures and pads

A shed or equipment pad is usually a reinforced slab over a compacted gravel base, often with a thickened edge. Size it to the building plus a little extra, keep it level for the structure while still shedding water at the edges, and confirm it meets setbacks from property lines, easements and utility lines. Many cities around Denver require a permit for accessory buildings over a certain size, and HOAs often have rules on size, location and materials. Check both before you pour.

Garages and workshops

A slab that will carry vehicles, heavy tools or equipment generally needs more thickness and reinforcement than a shed pad, plus footings or thickened edges to carry the walls. If you plan to heat or finish the space, ask about a vapor retarder, insulation and where conduit or plumbing should be placed before the pour. On swelling soil, garage slabs are often built as floating slabs, separated from the foundation walls so the floor can move without pushing on the structure.

Additions and expansive soil

Foundations for additions carry the building and have to be designed for the soil. The Colorado Geological Survey recommends site-specific investigation, including swell testing, where expansive clay or claystone bedrock is present, and Colorado builders must disclose known expansive soils to buyers of new homes. For an addition, that often means a soils report and a foundation designed by an engineer, which may call for drilled piers, a structural floor or other measures rather than a simple slab. Expect a building permit, inspections before concrete is placed, and a general contractor or builder coordinating the work.

Licensing in Colorado

Colorado does not issue a statewide general contractor or concrete contractor license. Licensing and registration are handled by cities and counties, and requirements differ. Denver, Aurora, Lakewood and Arvada each have their own contractor licensing or registration, and work in the public right-of-way usually requires a separate right-of-way license. Ask any contractor which local licenses they hold and who will pull the permit.

Site factors around Denver

  • Soil: footings should bear on firm soil, and expansive clay may call for engineered solutions instead of a standard footing.
  • Frost: footings must extend to the frost depth set by your local building code.
  • Drainage: keep the slab above grade and slope the ground away so water doesn't collect against the new structure.
  • Utilities: Colorado law requires contacting Colorado 811 before digging so underground lines can be marked.

Questions to ask

  • Does this project need a permit, and who will pull it?
  • Do we need a soils report or engineered foundation design?
  • How thick is the slab, and what reinforcement and base are included?
  • Will the slab be isolated from walls or footings so soil movement doesn't transfer?

Planning a building or an addition? Request a slab or foundation contractor and include the structure's size and use.

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Frequently asked questions

Does Colorado license concrete contractors?

Colorado does not issue a statewide general or concrete contractor license. Cities and counties handle licensing and registration, and right-of-way work usually needs a separate local license. Ask contractors which local licenses they hold.

Do I need a soils report for an addition?

Often, yes. The Colorado Geological Survey recommends site-specific soil investigation where expansive clay or claystone bedrock is present, and many building departments expect an engineered foundation design. Ask your building department and builder.

Do I need a permit for a shed slab?

Many Denver-area cities require permits for accessory buildings above a certain size, and HOAs often have their own rules. Check with your city or town building department and HOA before pouring.

Sources and further reading

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