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 = 16” Single story, brick veneer over wood frame = 16” Minimum Width of Concrete or Masonry Footings chart Assumes soil with bearing capacity of 2000psf

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 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

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

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

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 Lintels 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

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

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

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

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

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

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

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

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

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

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

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)

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

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

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