BEFORE THE ARCHITECT – CUSTOM HOME DESIGNING BACKGROUND – HOUSE DESIGN ARTICLES
ALL ABOUT HOUSE FOUNDATION PROBLEMS and YOUR HOME PAD FOOTING DESIGN
By Before The Architect Copyright 2009
YOU MAY FREELY QUOTE THE AG WITH PROPER ATTRIBUTION
Symmetry? The eye
looks for it, the mind's eye expects it, the mind is comforted by it. It's a
designer's habituation. Reined in this side of obsession, it suits principles
if not purposes. Be not smitten. It may be likened to the frame around a
painting and may be artful; it's not art. At its best, it counterpoints
inspiration, its complement. At its worst, it’s inspiration’s antonym, a kiss
from your sister. Before The Architect
QUESTION: WHASSUP WITH HOUSE FOUNDATION
PROBLEMS?
ANSWER: PRETTY NEAR NOTHING WITH A GOOD HOME
FOUNDATION PLAN.
SPREAD FOOTING IN A HOME FOUNDATION PLAN
Introduction
 | This article is about a home foundation spread footing |
o Design
o
Construction
Comment: Before The Architect (BTA) assumes
that these spread footings as with all other footings are sited on substrates of
reasonable bearing capacity and engineered when needed – a condition that, in
BTA’s experience, is very most often readily identifiable even in the design
stage, and, if not, then onsite.
| As with most other footings, a spread footing can go by other names, and ‘footer’ can be substituted for ‘footing’ |
o Footer
o Footing pad
o Individual footing
o Isolated footing
o Pad
o Pad footing
o Post pad
o Single footing
o Spot footing
o Spread footing
o DIY pad
o Precast footing
o Spread beam
| There are other common, concrete footings, don’t you know? |
o Grade beam
o Modified grade beam
o Turndown footing
| This custom home designer’s experience is that spread footings are less likely of footings to be engineered, closely tied with turndown footings for being made on the fly |
o Easy
o
More often overbuilt at minimal
marginal cost increment
| In BTA’s book, a spread footing |
o Shall be in most applications
§ Monolithic
§
Regular in all aspects
Spread Footing With Pier, Section in Elevation, Scaled
KEY:
ABV=ABoVe; APX=APproXimately; BEL=BELow; BOF=Bottom Of Face; BOT=BOTtom;
CONC=CONCrete; CONT=CONTinuous; CVR=CoVeR; D=Depth; DIA=DIAmeter; DIR=DIRection;
DN=DowN; EQV=EQuiValent; FDN=FounDatioN; FGL=Finish Grade Level; FSN=FaSteN;
FTG=FooTinG; GaLVanized; MIN=MINimum; NGT=Not Greater Than; NLT=Not Less Than;
PT=Preservative-Treated; RR=RebaR; SF=Square Feet; SUBS=SUBStrate; T&B=Top &
Bottom; TOF=Top Of Face; TYP=TYPical; W=Width; W:C=Water-to-Cement ratio;
WL=WaLl
o Shall be reinforced by
§ Not less than 4-Grade 50-#5 rebar in rectilinear pattern
§ With 3/4 linear inch plus maximum aggregate diameter cover and not more than 3 linear inches cover, which can devolve to two layers with a thickened pad
o Bottom of face shall be not higher than the bottoms of face of new, proximate footings
o If with pier, or pedestal
§ Then shall not be less than half the width dimension of the spread footing
§ Then shall be reinforced on the vertical with not less than 2-#5 rebar from the footing bottom of face plus 3/4 linear inch plus maximum aggregate size cover to the pier top of face less 3/4 linear inch plus maximum aggregate size cover and in either case not greater than 3 linear inches cover
Comment: The spread footing in the
illustration to follow is notable for at least one indication; namely, it can be
envisioned from any orthogonal as the same section.
Comment: The home design author notes an
historical reference; namely, this drawing executed some time ago specifies #4
rebar, a sizing OK in its time (not so long ago); however, these days, BTA
specifies not less than #5 in residential applications of reinforcement –
deformed generally, smooth or sleeved across contraction, or control, joints
exceptionally. Further, this custom home designer sees such up-sizing more
rather than less frequently in home design and home building as time passes.
| Where to design-in a spread footing |
o Specifically, BTA applies spread footings in 3 conditions
§ Below a grade beam
§ Below a modified grade beam
§
Below anywhere else that a point
or concentrated load path to earth travels or is otherwise guided to travel
| Below a grade beam |
o
Here’s an example of a spread
footing with pedestal, or pier, below a grade beam
Spread Footing Below Grade Beam at Intersection with Modified Grade Beam, Plan View, Scaled
KEY:
ABS=ABSOLUTE; BEL=BELOW; BM=BEAM; BOT=BOTTOM; BOT=BOTTOM; BW=BOTH WAYS;
CONT=CONTINUOUS; CVR=COVER; D=DEPTH; FTG=FOOTING; GD=GRADE; HOR=HORIZONTAL;
JT=JOINT; LI=LINEAR INCH; NGT=NOT GREATER THAN; NLT=NOT LESS THAN;
PRM=PERIMETER; RR=REBAR; SOG=SLAB-ON-GRADE; SPD=SPREAD; T&B=TOP & BOTTOM;
TOF=TOP OF FACE; TYP=TYPICAL
| Spread footing below a modified grade beam |
o
Here’s an example of a spread
footing below a modified grade beam
Spread Footing Below Modified Grade Beam Intersections, Plan View, Scaled
KEY:
BOF=BOTTOM OF FACE; CL=CENTERLINE; CONT=CONTINUOUS; CVR=COVER FTG=FOOTING;
GBM=GRADE BEAM; INT=INTERIOR; LI=LINER INCH; MIN=MINIMUM; NLT=NOT LESS THAN;
OC=ON CENTER; RR=REBAR; SIM=SIMILAR; SOF=SIDE OF FACE; SOG=SLAB-ON-GRADE;
SPD=SPREAD; TYP=TYPICAL
| Spread footing anywhere else that a point or concentrated load path to earth travels or is otherwise guided to travel |
§ Generally, load paths
ü Interior to perimeters or otherwise
ü Not to interior t-walls
§ Specifically among others –
ü Feet of a pool table
ü Interior, bearing columns
ü Exterior, bearing columns
ü
Pedestals to certain fireplaces,
e.g., Rumfords
| Here’s an example of an interior bearing column supported by a spread footing |
o
Which beam is double-decked,
that is, set atop another such wing wall on L0 and L1 to distinguish entrance to
important space on each level
Spread Footing Below Interior Bearing, Plan View, Scaled
KEY:
AB=ANCHOR BOLT; ABS=ABSOLUTE; BEL=BELOW; BM=BEAM; BOT=BOTTOM; BW=BOTH WAYS;
CONT=CONTINUOUS; D=DEPTH; EL=ELEVATION; FTG=FOOTING; GD=GRADE; GRD=GRADE;
HOR=HORIZONTAL; JT=JOINT; LI=LINEAR INCH; NLT=NOT LESS THAN; PNL=PANEL;
PRM=PERIMETER; PSG=PASSAGE; RR=REBAR; SOG=SLAB-ON-GRADE; SPD=SPREAD; TOF=TOP OF
FACE; TYP=TYPICAL
| Of note – |
§ Referenced to indicate places where anchor bolts shall not be set and for which compensation shall be made (dimensions that site these features are herewith omitted for clarity of expression)
§ Mullioned consonant with respectful observation of Traditional Style befitting this particular exterior (and a common sense approach to framing)
o Changes in elevation respect the reality of a walk-out, covered deck 6 linear inches below the habitable interior
o The control, or contraction, joint in the grade beam is off-center, forced so by a need to square-up the joint at its terminus with the wall and still centrally bear critical path loads from the roof, three ceilings and two floor systems
o
This spread footing is not
square in plan view, but rather rectangular – some would call it irregular –
because this designer’s not entirely sure where in the wing walls will an
engineer set the columns either side of a broadly opened portal or even whether
more than one column will be applied to either side, since this designer
indicated on the L0 and L1 floor plans that more than one column thereabouts
would be in-style
Comment: While not specified herewith, the custom home designer
expects, that in gauging the engineered beam, that engineer will further specify
the spread footing as seen fit.
Comment: Please note, dear reader, that in all instances, sub-slab-on-grade foundation elements are continuously separated at their top of face from the bottom of face of a slab-on-grade by a continuous bond break.
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