How to Build a Garage Foundation

Building a garage is an endeavor that some leave to the professionals.  If you have patience, fundamental construction skills and the right tools, you can build all or part of a garage yourself.  The first and most important part of your garage construction is building the foundation.  Follow a few straightforward steps and you will be ready to start building your garage. 

Whether you are planning to build a garage from scratch or have purchased a prefabricated garage, you will need to start with a solid, well-built foundation.  The foundation needs to be solid enough to support your vehicle, as well as all the equipment you plan to store in your garage.  Take some time to plan ahead and this activity can be accomplished in a day. 

Supplies you will need:

• Stakes


• Lime


• Can


• Shovel


• 2x10 boards


• 2x6 boards


• ½ inch rebar


• Foundation bolts


• Diesel fuel or non-stick concrete spray


• Sand


• Vapor barrier


• Concrete

Here are the construction steps:

1. Measure the area you will build your garage. Mark the outside of the foundation area with stakes.  Put lime in a can and make a chalk line to mark the perimeter.


2. Dig a 20 inch deep, 1 foot wide trench for your footings, on the inside of your chalk line.  Make sure you are following your plans during this stage of the project. 


3. Place the 2x10 form boards in place. Use stakes to hold them in place on the outside of the perimeter.  Make the forms 6 inches higher than the finished height of the planned concrete slab, to form the outside of the foundation’s curb.  Use a level to ensure the top of each form is level. 


4. Place the 2x6 boards to form the inside of the curb, six inches from the inside of the outside board.  Use stakes on the opposite side of the planned curb to hold them in place.  Forms should be in place on three sides of the garage, with 2 to 3 feet on each side of the door opening.  Use the level on these forms as well. 


5. Add an inch of sand to the forms, the vapor barrier and another inch of sand. 


6. Place the rebar in the forms, running horizontal to the forms.  There should be two sets of rebar inserted about 3 inches from the bottom and top of the planned curb. 


7. Use your design plans to identify and place bolts for sill plates, where needed. 


8. Spray the inside of the forms with diesel fuel or non-stick concrete spray, to ensure the concrete will not stick to the wood.


9. Pour 1 inch of sand on the bottom of the curb, as well as the slab area.  Put down the vapor barrier and then another inch of sand.  Lightly wet the sand.

10. Lay out rebar in the slab area using a grid pattern, 16 inches on center.

11. Pour the concrete into the footings. Allow it to come up to the top of the forms.

12. Wait two hours. Remove the inside form and pour the garage slab.

13. Wait another two to four hours and you can remove the outside forms.

14. You can begin construction on your garage about two days after pouring your footing, if you are in a rush.  Five to seven days will allow your foundation to fully cure.