How to Add Living Space With Using More Concrete


The foundation of the addition is—well, its foundation. The beefier it is, the stronger and longer lasting the addition will be. However, as in the case of improved electrical or plumbing systems, a better founda­tion will not bring in more money when it’s time to resell. On the other hand, you might not be able to sell at all if the foundation is broken. Also, if you’re going to live in the property for a while, you will proba­bly want to do a good job even though you are unlikely to recoup your investment. In this case, a good job usually means more concrete.

If you’re adding a room, you’ll need at minimum a peripheral foundation (one that runs along the outside edge of the addition)-Most foundations (but not all) are made of concrete. Your local building department will specify the type of foundation and its size.

Concrete Work

The most common type, a T foundation, actually looks like an inverted letter: J.. The footings, at the bottom, are wider than the wall at the top. The building department will specify the depth of the footings and the width. Since T foundations are typically used on flat ground, they tend to be fairly shallow. However, if there is a problem with the soil, such as expansion in wet weather, the footings may need to go deeper.

My suggestion is that, whatever depth and width the building department requires, go a couple of inches wider and deeper. The cost won’t be that much more and you will dramatically increase the likelihood of getting a truly strong foundation.

Use extra rebars (reinforcing steel bars). Rebars are placed in the concrete both horizontally (running with the walls) and vertically at various distances. Typically there will be at least two rebars running along the foot­ings. If the footings are deeper, two levels of rebar may be used. Again, additional rebars won’t cost that much more, particularly for a small addition, and will increase the strength of the foundation enormously. Later, even if the foundation should crack, the rebar will keep it in place.

There are many other types of foundation you may need to use, depending on the conditions of the soil. You might want to sink steel pins down to a supporting soil. Or you could use drilled concrete piers (considered better than steel pins) down to a supporting soil.

Many home additions today feature a “slab” or concrete floor rather than a true foundation. Typically a piece of reinforced con­crete, four to six inches thick, is poured inside a peripheral founda­tion to serve as the subfloor for the addition.

Home Concrete Work

When building on a hillside, use a steplike structure to create a stronger foundation with more support for the addition.

Be sure that the mix of concrete is good. When you order concrete from a supplier, you can specify the amount of water, sand/gravel, cement, and additives (various plasticizers). Among other things, the mix will determine how long the cement remains liquid and, hence, workable. However, too much water can weaken the final product. Generally speaking, concrete with less water, which sets up faster, will end up being stronger than concrete with extra water added so that it will set up slower.

Check the strength of the concrete. When the concrete for a foundation is being poured, samples are placed into special cans (they look like gallon coffee cans). These are typically tested at 7, 14, and 28 days. At the end of 28 days, the concrete should be completely cured to a hardness of at least 2800 psi (pounds per square inch). You’ll have to pay a test lab (which sup­plies the cans) to squeeze the concrete through a hydraulic press to make sure it measures up. In some cases the building department may require this test, but even if it doesn’t, you should assure yourself of the quality of the concrete used.

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About the Author: Jason Prickett loves to write about home maintenance and stuff you can do yourself instead of hiring any professional. His step by step guides will assist you in completing your home maintenance tasks.

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