Chapter 33

Foundation Systems

Introduction• All structures are required to have a

foundation– Provides a base to distribute weight onto soil– Must be evenly distributed to prevent it from

compressing the soil– Must resist floods, winds, earthquakes, and

floodwater debris

Soil Considerations• Soil texture

– Affects ability to resist load of foundation• Bearing capacity must be known

– Structures built low bearing capacity soil require footings

Soil Considerations (cont’d.)• Compaction methods

– Static force– Impact forces– Vibration

• Freezing– Foundation should be built to a depth where

ground is not subject to freezing• Expansion and shrinking can cause cracking

Soil Considerations (cont’d.)• Water content

– As soil absorbs water, it expands• Causes foundation to heave• Resisted through proper drainage and reinforcing

foundation and floor slab

• Radon– Cancer-causing gas

• Structures built in areas with high levels must provide protection

Types of Foundations• Piling foundation system

– Beams are placed between vertical supports (i.e., piling) to support structural loads

• Steep hillsides• Where structure load exceeds soil bearing capacity• Sites subject to flooding or natural forces that cause

large amounts of soil to be removed

Types of Foundations (cont’d.)• Continuous or spread foundation

– Most common for residential construction– Consists of a footing and wall– Concrete strength must be specified– For areas of soft soil or fill material,

reinforcement steel (i.e., rebar) is used

Types of Foundations (cont’d.)• Grade beams

– Added support for a foundation in unstable soil

• Fireplace footings– IRC requires minimum footing 12" deep and

extend 6" past fireplace face

• Veneer footings– Must be wide enough to provide adequate

support

Types of Foundations (cont’d.)• Foundation wall

– Vertical wall • Extends from top of footing to first-floor level

– Usually centered on footing to spread loads– Follow IRC and municipal requirements

Types of Foundations (cont’d.)• Additional considerations for the foundation

wall– Stem wall construction– Anchor bolts– Termite protection– Wood floor support– Wood floor ventilation and access– Foundation wall insulation and reinforcement

Types of Foundations (cont’d.)• Retaining or basement walls

– Extends full height between basement floor and main floor level

• Primarily made of concrete blocks, poured concrete, or concrete-filled insulated concrete foam blocks

• Material used will depend on area trends

Types of Foundations (cont’d.)• Additional considerations for retaining or

basement walls – Retaining wall reinforcement and anchorage– Moisture protection– Foundation windows

• Treated-wood basement walls– Pressure-treated lumber can be used to frame

crawl space and basement walls

Types of Foundations (cont’d.)• Partial-height retaining walls

– When a structure is built on a sloping site, retaining wall will not need to be full height

– More problems are encountered

Types of Foundations (cont’d.)• Interior load supports

– Supported on spot footings or piers

• Metal connectors– Used at the foundation level to resist stress

from wind and seismic forces

Dimensioning Foundation Components