7 Garage Foundation Tips You Should Know About

Building a concrete foundation for your garage plays a crucial role in the lifetime of the garage. A garage foundation is typically made of a concrete block wall and poured concrete. It is the most important key to supporting the structural integrity of the garage. It may look like a lot of extra work, but building the garage on a well-maintained foundation prevents many problems and grants the garage decades of reliable use. Unfortunately, foundation problems are not always easily apparent, especially if you are not intentional about checking them. The best way to avoid future garage foundation problems is to install it right when building the garage! Most homeowners choose to hire site preparation professionals who have seasoned experience and accurate knowledge about foundations, rather than attempting a DIY garage foundation. Here are some useful tips that every garage owner should know before building their garage.

Trench for a garage foundation
Garage footer

1. Soil Preparation For Garage Foundation

The main threat to your garage foundation comes not from what gets built or assembled on top, but comes from what might move below. The soil you build your concrete foundation on needs to be compact and well-maintained to get the best concrete foundation results. If the soil or base beneath the foundation settles or moves, the result can be a gapped or cracked foundation.

Good preparation of the building lot starts with removing the topsoil. After that, a trench is dug for pouring reinforced concrete footers. In most areas of the United States, garage footers are usually dug 36 inches below the final grade. The footer size is typically 20 inches wide and 8 inches deep. If your township requires something different, it will be done according to your municipality requirements. When you take the steps to prepare the soil, you limit the risk of settling in the ground causing cracks in your garage foundation.

Vapor barrier for concrete foundation

2. Vapor Barrier For Concrete Foundation

After filling the inside of the foundation with at least 4” of ¾” inch clean stone across the entire foundation, it’s a good idea to add a vapor barrier to prevent condensation on your garage floor. A 6 mil plastic vapor barrier is a typical material.

Vapor barriers are usually sheets of plastic. It is an inexpensive bit of insurance against water moving up through the porous concrete. It prevents damage to items placed on the garage floor. Garage foundation vapor barriers are manufactured specifically for use under concrete.

Concrete mixture for a garage foundation

3. Choosing The Right Foundation Mixture

The garage foundation should be a minimum of four inches thick when placed on good soil. It may need to be thicker if the garage will be home to unusually heavy equipment. The amount of water used in the foundation mixture is determined by the standards. Although adding more water makes pouring easier, it can also make the foundation weaker. If you live in a cold climate, your concrete mixture should include air-entraining agents, which limit damage to the foundation through seasonal freeze cycles.

Typically, when pouring a concrete garage foundation, you will simply order the concrete from a local concrete supplier according to the PSI rating your building drawings require. The concrete company will take care of the exact mixing ratios for the materials.

Adding reinforcement for a concrete foundation

4. Garage Foundation Reinforcement

Fiber, wire mesh, or thick reinforcement rebar is an important component of concrete foundations. Fiber reinforcement has become popular in recent years as an inexpensive product that matches up well to wire mesh reinforcement in many tests. The fibers are usually mixed in with the concrete to increase structural strength and produce a stronger foundation. Many contractors like Site Prep now add fiber reinforcement to every concrete garage foundation they pour.

Expansion joints for a garage foundation

5. Expansion Joints

What is a concrete expansion joint? A concrete expansion joint is designed to prevent random cracking by giving a predefined location for a concrete foundation to crack. Expansion joints are normally placed in concrete foundations to prevent expansive cracks formed due to temperature change, ground settlement, and soil movement due to earthquakes. Concrete foundations expand and contract with changes in temperature and moisture. If this expansion is not controlled properly, cracks can begin to appear and may run in any direction, or in multiple directions. For that reason, the expansion joints play an essential role when pouring a concrete foundation.

Expansion joints should be at least 25% of the total thickness of the foundation. Expansion joints will be made by sawing into the hardened concrete surface. It is important to understand that the longer sawing is delayed the higher the potential for cracks to establish themselves before sawing is complete. For instance, one inch deep cut would be required for a four inch thick pour. Expansion joints will then be created after the concrete is poured.

Expansion joints for a concrete foundation

Concrete foundations will perform very well when following the considerations listed above. Secure the success of your next foundation project by taking some time to learn more about concrete foundations.

6. Building A Concrete Foundation On A Hillside

There are several options for building a garage on a hillside, such as digging out and building the garage foundation into the slope or building up one end of the garage foundation. When planning and implementing a garage foundation on a slope, make sure to secure expert advice. This will be invaluable in ensuring that the slope does not pose a risk to your garage or its foundation. Professional advice at the outset can help to prevent possible complications with the overall design of the garage.

7. Finishing Your Concrete Foundation

After the concrete has been poured, the foundation needs to be leveled and smoothed properly. Expansion joints should be measured and cut into the wet concrete to provide additional crack resistance. It is recommended to do this within the first 6to 18 hoursand never delay more than 24 hours. Then, the concrete foundation needs to be left alone. It doesn’t dry out; it rather undergoes a chemical process that creates a solid, cured mass. As the concrete sets, it’s common to use power trowlers to finish the top of the concrete foundation into a smooth surface for the garage floor.

Now that you know the basics of a properly placed garage foundation, you can compare several different concrete garage foundation styles here. You can also watch this video for a visual overview of how we install concrete foundations in the Mid-Atlantic USA.

10 thoughts on “7 Garage Foundation Tips You Should Know About

  1. Site Preparations LLC says:

    Hi SC,
    You’ll want to contact a local contractor that has experience working with the ground conditions in your area. Best wishes!

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  4. Robby says:

    I live in unincorporated Logan County, Oklahoma. No building permits required here. My area where I want to put a concrete pad is on a grade. Is it better to dig into the grade and put a wall around the area that you want to put a concrete pad? Or is it better to bring in something like road base and build up the area you want to put the concrete pad for a new metal garage?

  5. Site Prep says:

    Hi Robby, we would build a retaining wall around the lower side and fill it in with concrete, the main side, where the doors are, should be roughly 3 inches above the grade.

  6. Philip Capaldi says:

    I’m doing a garage conversation turning it into a bedroom with bathroom for my wife who is disabled. The garage only had one brick wall and the cable end of the house being the other with double garage doors at each end, we’ve now discovered the previous owner had only used 10cms of cement for the outer wall so am I right in thinking that this will have to be taken down and a new wall constructed with a 600 mm concrete base any reply or advice would be gratefully received Thankyou

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