In many parts of North America, building codes don’t require steel reinforcement in concrete foundations, but steel is a cost-effective means of avoiding cracks caused by lateral pressure on foundation walls.
Steel reinforcement and fasteners. Steel reinforcing bar (rebar) basically carries and distributes loads within the foundation, transferring the loads from high-pressure areas to lower-pressure areas. It thereby lessens the likelihood of point failure, either from point loading above or from lateral soil and water pressures. Anchor bolts or threaded rods, tied to rebar, attach the overlying structure to the foundation. Steel dowels are usually short pieces of rebar that pin foundation walls to footings, new sections to existing foundations, and so on.
There are also a number of metal connectors— such as Simpson Strong-Ties—that tie joists to girders, keep support posts from drifting, and hold down mudsills, sole plates, and such.
Several are shown in Chapter 4.
Quality. Concrete quality is critically important, both in its composition and in its placement. Water, sand, and aggregate must be clean and well mixed with the cement. Concrete with compressive strength of 2,500 psi to 3,500 psi (pounds per square inch) is common in residential founda-
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Most perimeter foundations have a companion foundation within, consisting of a system of girders (beams), posts (columns), and pads that pick up the loads of joists and interior walls and thus reduce the total load on the perimeter foundation. By adding posts, beams, and pads, you can often stiffen floors, reduce squeaks, avoid excessive point loading, support new partitions, and even avoid replacing a marginally adequate perimeter foundation.
GETTING THE
Learn what you can about local soil conditions before hiring a soils engineer. Start with local builders—especially those who’ve worked on nearby properties. Next consult with building and land-use departments, for many have maps indicating watersheds, slide zones, contaminated soil, and the like. Finally, the U. S. Department of Agriculture (USDA) has extensive soil maps. And the U. S. Geological Survey (USGS) topographic (topo) maps show streams, lakes, flood plains, and other natural features that could have an impact on your site.
tions, yet there are many ways to achieve that strength, including chemical admixtures. Discuss your needs with a concrete supplier who’s familiar with soil conditions in your area, and read "Ordering Concrete,” on p. 222.
Drainage. The drainage system is not technically a part of the foundation, but the flow of water alongside and under a foundation is important to its success. In some soils, it’s essential to mediate water flow. At the very least, water seeping through foundations can cause damp basements and encourage mold. Worse, excessive water can rot framing, undermine footings, and cause unreinforced foundations to crack, bulge inward, or fail altogether. Often moisture problems can be mitigated simply by keeping gutters and downspouts clear, grading the soil away from the foundation, and improving drainage around basement window wells. Beyond that, the "cures” are increasingly expensive, such as excavating along the outside of the foundation to add gravel and perimeter drainpipe and to apply waterproofing treatments.
