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Structural

Foundation

In Plain English

The part of a building below grade that transfers all weight to the ground.

Definition

The lowest structural element of a building that transfers all loads from the structure to the supporting soil or rock. Foundations are classified as shallow (spread footings, mat foundations) or deep (piles, drilled piers) depending on the soil conditions and load requirements. A properly designed foundation prevents settlement, movement, and structural failure.

Why It Matters in Bidding

The foundation scope carries some of the highest cost and risk uncertainty in any bid because it depends on subsurface conditions that may not be fully known until excavation begins. Estimators rely on the geotechnical report to price the right system, spread footings versus piles or piers, and differing site conditions are a leading source of foundation change orders, so how this risk is allocated in the bid documents directly affects who absorbs an overrun.

Example

After the geotechnical report called for drilled piers instead of spread footings, the GC requested clarification before bid day because the deep-foundation system added significant cost the original budget had not carried.

Related Terms

FootingDeep FoundationGrade BeamSlab-on-Grade

Frequently Asked Questions

Shallow foundations such as spread footings and mat slabs distribute loads near the surface and cost less where soil is competent. Deep foundations like piles and drilled piers transfer loads to stronger strata far below grade and cost substantially more in equipment and labor. The geotechnical report dictates which system the bid is required to price.
The geotechnical report defines soil bearing capacity, water table, and recommended foundation type, which drives the entire foundation scope and price. Without it, an estimator is guessing at footing sizes and depths. A late or unfavorable report can force a switch from inexpensive footings to costly deep foundations, materially changing the bid number.
Subsurface conditions stay hidden until excavation, so actual soil, rock, or groundwater often differs from the assumptions in the borings. Differing site condition clauses determine whether the owner or contractor pays when conditions prove worse than expected. This uncertainty makes the foundation one of the most disputed and contingency-heavy line items in a bid.

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