Page 194 - Masonry and Concrete

Footings, Foundation Walls, Basements, and Slabs
193
FOOTINGS, FOUNDATION WALLS, BASEMENTS, AND SLABS

the entire foundation wall, especially if its
height is more than a foot or two.
For footings 12 in. or less in thickness, 1 /2W W 1 /2W
formwork is easiest to build of 2 lum-
ber because there is less cutting required
than for making short plywood forms.
Remember that the actual size of the lum-
1
ber is 2 in. less than its nominal dimen-
sion. Using 2 6s for a 6-in.-thick
W
footing, for example, requires that the
boards be set slightly off the ground to
achieve the required dimension. To keep
the concrete from running out the bottom
2W
of the forms, backfill with a little soil
MIN. REQUIRED BY
after the forms and braces are in place CODE IF GREATER
(Figure 6-6). If a footing is 8 in. or more in THAN 2W
thickness, use 1 4 spreaders spaced FIGURE 6-5
about 4 ft. apart along the top of the forms
Rule-of-thumb footing size requirements.
to keep the concrete from bowing them
out of shape (Figure 6-7). A beveled 2 4
should be inserted lengthwise along the top of the footing to form a
keyway which will keep the wall from sliding. The keyway form
should be well oiled so that it will be easy to remove after the con-
crete has hardened. Concrete walls set on top the footing will inter-
lock physically along the indentation. The bottom course of a
masonry wall should be set in a full bed of mortar which will also
interlock slightly to prevent sliding.

6.2.2 Stepped Footings

Where the ground under a wall slopes slightly, you can build a foot-
ing that is level but is deeper in the ground at one end than the other.
Where the ground slopes more steeply, though, it is best to step the
form down the slope so that the footing is in a series of level sections
(Figure 6-8). For footings with lumber forms, build two overlapping
forms to create the change in height (Figure 6-9), making sure that
the overlapping portion is at least as long as the footing is thick.
That is, for an 8-in.-thick footing, overlap the two adjoining levels at
least 8 in.

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.