1. Competency: 304.00 Design and Draw Foundation Plans
Objective:
Design footings, foundation walls, girders, piers, ventilation, and slab floor/foundations.

2. Continuous Wall Footings Footing Size
Engineering data regarding soil & structural loads
NC Building Code minimum footing widths
Single story, conventional wood frame = 16”
Single story, brick veneer over wood frame = 16”
Minimum Width of Concrete or Masonry Footings chart
Assumes soil with bearing capacity of 2000psf

3. Continuous Wall Footings Footing Size
“Rule of thumb” based on thickness of foundation wall
Width = 2 x foundation wall thickness
Depth = foundation wall thickness
Assumes firm, undisturbed soil or engineered fill
Minimum soil bearing capacity of 2000 psf

4. Continuous Wall Footings Steel Reinforcement
Controls tension forces
Two longitudinal rebars in bottom of footing carry tensile loads
Prevents spreading
Tension forces occur only in bottom portion of footing
Top portion of footing is in compression

5. Continuous Wall Footings Steel Reinforcement
Bar size based on 1/8”
Example: #4 bar = 4/8” (1/2)
Transverse bars tied to longitudinal bars at regular intervals
“Chairs” hold bars in place
Footing thickness to width ratios require increases in widths, turn, thickness

6. Continuous Wall Footings Steel Reinforcement
Stepped footings
Vertical and horizontal parts resembling steps
Vertical step no more than ¾ the distance of horizontal depth
Reduce excavation and materials costs on hilly terrain
8” module used when concrete block is used for foundation wall

7. Foundation Walls
NC Residential Building Code determines concrete & masonry wall thickness
Unbalanced fill
Height of earth pushing against foundation wall
Wet soil produces greater pressure than dry soil
Type of wall construction
Hollow
Solid
Grouted

8. Foundation Walls
Lateral resistance to earth pressures provided by intersecting walls, floors, and pilasters
Pilasters are posts built into a wall
Supports for beam endings and resistance to pressure
Masonry units are interlocking with units in alternating direction
May be filled with grout and/or steel rebars

9. Foundation Walls
Poured concrete walls can be reinforced with steel rebars placed in tension zone
Poured concrete walls can be tied to poured concrete footings using “keys” formed into footing
Foundation walls located in center 1/3 of footing
Extends minimum of 8” above grade with wood construction

10. Foundation Walls Minimum distance 7’-0” floor to ceiling in a basement
Lintels
Structural members over openings in masonry walls
4” minimum bearing
Steel or masonry

11. Foundation Walls Damp Proofing
Heavy coats of tar or two coats of cement based paint for basement walls
Thin coats of cement-mortar materials or parging
Polyethylene or plastic sheeting
Thickness measured in “mils”
6 mil most common

12. Foundation Walls Damp Proofing
Drain tile
4” perforated pipe surrounds structure at bottom of wall
Set in washed gravel from wall
Covered with 6” washed gravel above
Holds back soil
Allows water to enter pipe
Water in pipe is carried away

13. Girders - Design Based on material, span, and load
Live and dead loads included
Determine load area(s) requiring support & multiply by sum of live and dead loads
Determine loads imposed by walls and significant features & add to area loads
Determine load per foot
Divide total load by length of beam

14. Girders - Design
Charts require load per foot of beam to calculate beam size and span
Load expressed in “kips”
1 kip = 1000 lbs
Modifications
Increase number of piers/columns to shorten span
Change material
Pier spacing remains equal
Change species/grade of wood

15. Girders - Design Beam charts limit size based on deflection
Deflection – amount of bending occurring when structural member is loaded
Limited to 1/360 of span

16. Girders
NC Residential Building Code charts for built-up wooden girders include pier & footing sizes
Determine area supported by pier
Appropriate chart for single or multi-level structure
Determine depth of structure
Determine interior or exterior girder
Select grad and species of lumber

17. Girders Read size of pier & pier footing from chart
Masonry pier height limited by size of pier & type of construction
Interior and exterior piers treated differently
Piers capped
4” solid masonry for single-story structure
8” solid masonry for multi-story structure

18. Piles Driven into soil or onto bedrock without separate footing
Supports heavy structures or those built on poor soils
Used when footings cannot be stabilized in loose soil
Beach homes built on loose sand

19. Piles Materials Treated wood Steel pipes filled with concrete
Steel beams
Bored holes filled with reinforced poured concrete
Pre-cast concrete

20. Foundation Ventilation
NC Residential Building Code minimum requirement is 1 sq. ft. ventilation for every 150 sq. ft. crawl space area
Vapor barriers reduce ventilation requirements

21. Slab Foundation Reinforced concrete floor and footing Monolithic pour
Footings may be poured separately
Requires less time and labor than T-foundation
Turned down extension extends below frost line
Perimeter insulation

22. Slab Foundation NC Residential Building Code requirements
Vegetation, top soil, foreign material removed
Below grade 4” slab poured on clean, graded sand, gravel, or crushed stone
Vapor barrier between slab & sub-grade
Where no base course is used
Not necessary in unheated structure
4” minimum slab thickness

23. Slab Foundation Concrete construction
Composed of cement, sand, stone or gravel aggregate, and water
Varying ingredient amounts change strength & properties
Cement composed of lime, silica, and other materials
Purchased by cubic yard (3’x3’x3’ = 27 cu. ft.)
Strength measured in PSI (pounds per square inch)

24. Slab Foundation Cures over a long period of time
Affected by temperature
Extreme cold slows curing
Extreme heat causes evaporation

25. Slab Foundation Cracking
Expansion and contraction due to temperature change
Moisture content
Large areas more likely to crack
Joints
Cut into fresh concrete with joining tool
Cut into cured concrete with masonry saw
Floor slabs not bonded to columns or walls

26. Slab Foundation Cracking (cont’d)
Expansion joints positioned next to walls
Building felt or fiberboard used as expansion joints
Fiberglass fibers may be used in mix rather than steel
Wire mesh reinforces slab
Pre-manufactured control joints in slab
Pressure-treated lumber placed where members abut concrete