Get Postholes Started on Right Footing

Whether you’re constructing a deck, adding a porch or building a gazebo, the job begins with footings that penetrate your climate’s frost line. In many cases, a simple posthole footing is ideal. This type of footing is quick, easy and relatively inexpensive. If you plan on an enclosed addition, of course, you’ll want a continuous footing that surrounds a crawl space beneath the floor. Anything short of a major structural addition will rest on simple posts and spot footings.

Before digging, check your local building codes. Generally however, spot footings will need to be 8 inches in diameter and at least 36 inches deep. Don’t be tempted to get by with shallower holes. If you don’t dig below the frost line, you run the risk of seasonal shifting and structural damage.

Pouring a posthole footing requires very little in the way of tools and materials. At the start, you’ll need a posthole digger--either a scissors or an auger type. You’ll also need a tape measure, level, shovel, galvanized post brackets and concrete.

Use a mortar box or wheelbarrow to mix the concrete. If you plan to pour a series of footings in a row, stretch a string between two stakes placed beyond the first and last posthole locations. With this in place, the holes can be aligned and each bracket can be positioned accurately.

If you plan to pour only a few footings, it’s easier to buy bags of premixed concrete--you simply add water. Each 60-pound bag will make 1 cubic foot of concrete. An 8-inch-diameter by 36-inch-deep footing will take about two bags.

After laying out and marking the footing locations, rough out each hole with the posthole digger. There’s nothing complicated about digging a hole, but make sure it doesn’t taper. Make the bottom of the hole the same diameter as the top and keep the sides consistent. When you’ve reached the required depth, trim the bottom of the hole flat and clean out all loose soil.

With the holes ready, prepare the premixed concrete one or two bags at a time. As a drier mix is always stronger than a wet mix, add only enough water to make the concrete workable. Then, shovel it into each hole until it reaches the grade level. Finally, float the tops of each footing so that the concrete is level and smooth.

Keep in mind that this isn’t a finished surface and you needn’t spend a lot of time smoothing with a trowel or small piece of lumber.

Setting a bracket in wet concrete is easy enough, as long as you position it exactly where you need it. Again, a taut string helps in positioning a row of brackets. Lacking the string, you can simply measure from a common point such as a foundation wall. With the brackets settled into the concrete, use a level in both directions to level the units.

After the concrete has set for several days, you can begin building on your footings. The mix will not reach full strength for several weeks, however, so avoid side stress on the brackets while building. When nailing lumber to a bracket, use approved bracket nails. These nails are short and thick and designed for optimum shear strength. While a standard galvanized nail may seem an acceptable substitute, many building code authorities won’t agree.