Unit 10 Foundation Prints 179
an elevation marked, for example, as TOF = 91′-4″
or T/FTG = 91′-4″. Refer to Figure 10-2A and
Figure 10-3. Sometimes, the bottom of the foot-
ing will also be marked as an elevation. For auger
cast piles, caissons, and steel piles, the top of the
pile cap (upon which the structure is going to be
built) is the elevation given. All the information
is defi ned in details and schedules. Each project
will have its own special elevation designation
system. Become familiar with the plans early in
the preconstruction phase to work out any coordi-
nation problems. Referring to Figure 10-2A, note
that the top of footing elevation is given as 95′-6″.
If the fi rst fl oor elevation is 100′-0″, this means the
top of the footing is 4′-6″ below grade.
Slab-on-Grade
A concrete slab poured at ground level is
called a slab-on-grade. Concrete slabs are used as
both basement fl oors and main fl oors. Basement
fl oors are poured after the footings and founda-
tion walls are in and sometimes, in residential
construction, before the rough framing starts.
Floating slab construction is a type of slab-
on-grade construction that uses a monolithic
slab (where the slab and footings are cast as one
continuous unit). See Figure 10-11.The footings
in this type of construction are sometimes called
turned-down footings. Another method of produc-
ing a slab fl oor is to fi rst pour the foundation walls
to fl oor height. Then, the area within the walls
is fi lled with soil and gravel. Finally, the fl oor is
poured within the walls, separated by an expan-
sion joint, Figure 10-12.
Loadbearing walls over slab fl oors require a
thickened slab, Figure 10-13. These areas are indi-
cated by hidden lines indicating the deeper por-
tion and a note.
Slab Reinforcement
A slab-on-grade is not considered a structural
slab, but can have reinforcement to assist in load-
carrying and resistance to cracking. Steel reinforc-
ing rods or welded wire fabric (WWF) are cast
in the concrete due to the slab being subjected to
Figure 10-12.
A slab fl oor poured within the foundation
walls.
Floating slab
Compacted fill or
undisturbed soil
Footing
Foundation wall
1/2" expansion joint
4" Gravel
SECTION VIEW
Reinforcing steel
PLAN VIEW
SECTION VIEW
Figure 10-13.
The slab is thickened to create a beam
below loadbearing walls.
Figure 10-11.
A monolithic slab foundation.
12" 4" 8" 4"
4"
6"
BELOW
FROST
LINE
Grade Stirrup
Gravel
Compacted fill
or undisturbed
soil
2 #4 Cont.
#3 at 12" O.C.
both ways
Masonry
ledge