Concrete offers a strong base on which to park your vehicles. If your driveway is too narrow or too short to handle all of your parking needs, you can extend it with additional concrete. Unless the extension is very small--less than a foot wide--hire a professional to pour it.
Dig the soil to a depth of at least 5 inches where you want to pour the extension. This includes the area right next to the current driveway. Clear away all the dirt and debris from the side of the concrete.
Build your concrete forms with 2-inch-by-4-inch dimensional lumber to the desired length and width of the extension. Drive stakes on the outside of the forms to brace the boards and nail the forms to the stakes.
Level the top board of your forms with a transit or a long carpenter's level. Account for the current slope of your driveway. A standard driveway will slope a minimum of one-quarter inch for every 4 lineal feet. After determining the slope of the existing driveway, adjust the top level of your forms to match the grade.
Fill the bottom of your forms with sand 1 or 2 inches deep. The sand stabilizes the concrete and will reduce future cracks.
Drill holes 6 inches deep on the exposed edge of your existing driveway and insert rebar rods into the holes. The holes should be halfway between the surface of the driveway and the base of the concrete. Space the holes 16 inches apart.
Use a hammer to drive the rebar rods into the holes. The rods should be long enough to come within an inch of the opposite edge of the forms. For instance, if you're adding a 2-foot strip to the side of your driveway, cut the rebar rods 29 inches long. This allows you to drive the rods 6 inches into the drilled holes, leaving 23 inches of rod extending to the other end of the forms.
Add additional rebar to the inside of your forms to comply with your local building codes. This rebar will run at a right angle to the rods inserted in to the existing driveway and you will connect them at the intersections with rebar ties.
Pour and shovel the concrete evenly, using a concrete screed, or a board, to level off the top. Use a hand trowel to work the concrete by rubbing back and forth until the surface is level.
Allow the concrete to cure undisturbed until hard, up to 48 hours, before stripping away the concrete forms and filling around the new driveway with soil.