![]() ![]() Any time you're in doubt about the soil under your foundation, you'd be wise to get professional help.īrent Anderson is a consulting engineer and concrete contractor who serves on the American Concrete Institute Committee 332, Residential Concrete. As you look at the solutions I recommend, however, keep in mind that high-bearing-capacity soil is assumed. IMI’s collection includes many common connection details between two or more architectural elements walls, roofs, floors and so on so crucial in ensuring a building. For the benefit of builders in the field and at the risk of oversimplifying, I'm going to use non-technical language in this article to briefly explain a little about how footings work and to present some ideas for dealing with special situations. That’s why they have created an extensive series of typical construction details, each fully modeled and freely available to download from SketchUp’s 3D Warehouse. I find that people understand the problems better if they have some background knowledge. I'm a consulting engineer as well as a contractor, and I get called in to a lot of problem situations. In weak or marginal soils, however, it's best to be very cautious some of the solutions contractors think up may not really work. In very strong soils, minor mistakes probably aren't a big deal. In these tough cases, it's helpful to understand the bearing strength of soil and the reasons behind footing design rules. Minimum thickness for plain concrete foundation walls shall be 7.5 inches (191 mm) except that 6 inches (152 mm) is permitted when the maximum height is 4 feet, 6 inches (1372 mm). 13) horizontal bar located in the upper 12 inches (305 mm) of the wall. But if the risk is low, you'd like to keep the job moving. Minimum reinforcement for plain concrete foundation walls shall consist of one No. If you think there's a problem ahead, you know you should stop and call an engineer. When the footing is laid out off-center so the wall misses its bearing, when you encounter a soft zone on site, or when the footing is undersized, the builder faces a judgment call. It's the unusual situations that cause the most trouble. A frame house with wood siding and drywall interiors can probably handle up to 1/2 an inch of differential foundation movement, but even 1/4 of an inch of uneven settling is enough to cause cracks in masonry, tile, or plaster. If the whole house settles slowly and evenly, some additional settlement is no big deal but if settlement is uneven (differential settlement), there could be damage. We don't often see outright failure, but it's not uncommon to see excessive settlement when soil bearing capacity is low. A footing that performs well in good soil may not do so well in weak bearing conditions. Guide to Residential Concrete ( ACI 332R-06) published by the American Concrete Institute, 38800 Country Club Drive, Farmington Hills, MI 48331 Phone: 24 Ed. On the other hand, if you build on soft clay soil or if there's a soft zone under part of your foundation, there can be trouble. Trench footing Shallow trench filled with concrete.Stepped footing Stair-like design spreads out load. ![]()
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