Quick answer: A home addition foundation is usually built in four stages: excavation, footings (the wide concrete base, reinforced with rebar), stem walls (concrete walls that rise from the footings to support the framing), and a slab or floor system. In Colorado, footings must go below the local frost depth, rebar is typically inspected before each pour, and the below-grade walls get damp-proofing to keep moisture out.
Step by Step: A Golden Home Addition
- Excavation: the trench is dug to the depth the plans and local code require.
- Footing rebar: an engineered rebar cage is tied in the trench and inspected before concrete, as shown in the photo above.
- Footing pour: concrete is placed with vertical rebar dowels sticking up to tie into the stem wall.
- Stem wall forms: forms are set and braced, rebar is placed, and the walls are poured.
- Damp-proofing: once the forms are stripped, a coating goes on the below-grade face of the walls.
- Slab: the base is compacted, wire mesh reinforcement is placed, and the slab is poured and finished where it ties into the existing house.
Why the Foundation Matters So Much
Colorado’s expansive clay soils and freeze-thaw cycles are hard on foundations. A foundation that’s too shallow, under-reinforced, or poorly drained can heave or crack, and that shows up later as cracked drywall, sticking doors, and a gap where the addition meets the house. Many Front Range additions need an engineered foundation design based on a soils report.
For costs and permits, see our home addition guides.
Foundations are where an addition starts. Learn more about working with a building contractor in Longmont.
Frequently Asked Questions
What is a stem wall foundation?
A stem wall is a concrete wall built on top of a footing that raises the structure above grade and supports the framing. It is common on Colorado home additions.
How deep do footings need to be in Colorado?
Footings must extend below the local frost depth, which is set by each city or county building department. Engineered plans may require deeper footings based on soils.
Do home addition foundations need an inspection?
Yes. Building departments typically inspect footing and wall rebar before concrete is poured, plus later stages of the addition.
Planning an addition? Josh Brooks Construction and Renovation is a licensed general contractor in Longmont with 30 years in construction, serving 46+ Front Range cities. Call 720-828-7997 or text 720-453-5095.
