Design and Draw

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25 Νοε 2013 (πριν από 4 χρόνια και 7 μήνες)

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Competency: 304.00

Design and Draw
Foundation Plans

Objective: 304.02

Design footings, foundation walls, girders,
piers, ventilation, and slab floor/foundations.

Continuous Wall Footings

Footing Size

Engineering data regarding soil &
structural loads

NC Building Code minimum footing widths

Single story, conventional wood frame =

Single story, brick veneer over wood frame
= 16”

Minimum Width of Concrete or Masonry

Assumes soil with bearing capacity of

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

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

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

Continuous Wall Footings

Steel Reinforcement

Stepped footings

Vertical and horizontal parts resembling

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

Foundation Walls

NC Residential Building Code
concrete & masonry wall thickness

Unbalanced fill

Height of earth pushing against foundation

Wet soil produces greater pressure than dry

Type of wall construction




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

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

Foundation Walls

Minimum distance 7’
0” floor to ceiling in
a basement


Structural members over openings in
masonry walls

4” minimum bearing

Steel or masonry

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

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



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



Charts require load per foot of beam to
calculate beam size and span

Load expressed in “kips”

1 kip = 1000 lbs


Increase number of piers/columns to
shorten span

Change material

Pier spacing remains equal

Change species/grade of wood



Beam charts limit size based on


amount of bending
occurring when structural member is

Limited to 1/360 of span


NC Residential Building Code

charts for
up wooden girders include pier &
footing sizes

Determine area supported by pier

Appropriate chart for single or multi

Determine depth of structure

Determine interior or exterior girder

Select grad and species of lumber


Read size of pier & pier footing from

Masonry pier height limited by size of
pier & type of construction

Interior and exterior piers treated

Piers capped

4” solid masonry for single
story structure

8” solid masonry for multi
story structure


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



Treated wood

Steel pipes filled with concrete

Steel beams

Bored holes filled with reinforced poured

cast concrete

Foundation Ventilation

NC Residential Building Code

requirement is 1 sq. ft. ventilation for
every 150 sq. ft. crawl space area

Vapor barriers reduce ventilation

Slab Foundation

Reinforced concrete floor and footing

Monolithic pour

Footings may be poured separately

Requires less time and labor than T

Turned down extension extends below
frost line

Perimeter insulation

Slab Foundation

NC Residential Building Code


Vegetation, top soil, foreign material

Below grade 4” slab poured on clean,
graded sand, gravel, or crushed stone

Vapor barrier between slab & sub

Where no base course is used

Not necessary in unheated structure

4” minimum slab thickness

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

Purchased by cubic yard (3’x3’x3’ = 27 cu.

Strength measured in PSI (pounds per
square inch)

Slab Foundation

Cures over a long period of time

Affected by temperature

Extreme cold slows curing

Extreme heat causes evaporation

Slab Foundation


Expansion and contraction due to
temperature change

Moisture content

Large areas more likely to crack


Cut into fresh concrete with joining tool

Cut into cured concrete with masonry saw

Floor slabs not bonded to columns or walls

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

manufactured control joints in slab

treated lumber placed where
members abut concrete