How to Build a Concrete Pad for a Garage 

After you place an order for a garage from Sheds Unlimited, its time to begin the foundation installation. If you are looking for a more permanent garage foundation that is the least resistant to settling and deterioration, consider getting a concrete foundation. There are several types of concrete pads that don’t provide a basement or crawl space. Site Prep lists some options, which includes a basic floating concrete pad, a more durable floating concrete foundation, a monolithic concrete foundation (one pour of concrete and a 36×10 frost wall), and the heavier-duty block foundation with 8×20 footer and block wall. We will be describing the block foundation in this guide (most of the process is taken from Site Prep’s block foundation installation method). You can also read Tom’s story on his 2 car garage with loft and see how he prepared his garage pad.

Not looking to build your own? Skip down to our common questions around concrete foundations, or go to our concrete foundation contractor referral page. Still looking for your garage or shed? Browse our options or design one in 3D.

NOTE: Sheds Unlimited is NOT responsible for structural problems if one fails to follow the instructions. Failure to follow instructions will void the Sheds Unlimited Warranty and may incur extra delivery charges!

Step-By-Step Process

How to build a concrete foundation…

1. Follow Local Guidelines

• Before you get deep into preparing the concrete pad for your garage, ensure that you understand your local building codes for a garage foundation. You will probably have to obtain a zoning permit and perhaps a building permit as well. Many times a foundation needs to pass inspection throughout the process if it is a permanent foundation and supporting a large structure. Some towns require a concrete pad with footers and certain specs and others allow for a simple monolithic pad poured on top of the ground. There are also almost always regulations on where the garage is allowed to go. For example, in some PA jurisdictions, any detached garage needs a zoning permit, cannot be placed within 5-10 feet of the property line, and must be located on either the side or rear of the property. As a homeowner, you are responsible for checking with local authorities to find out what is required. (For assistance, you can take a look at our articles on permits for garages in Maryland, New Jersey, and Pennsylvania.)

2. Choose the Site

Here are some things you may want to consider when choosing a place for your garage/shed. 

• As previously mentioned, you want to first get a good understanding of your municipalities guidelines so you know what plans/locations are allowable for you.
• Don’t choose a too-sloped area. This is going to complicate the installation process. And cost you more in the long run. Additionally, the foundation will have more potential to settle over time or deteriorate in some way.
• Choose solid, optimal ground. The more solid the soil, the less potential for settling. Consider the type of soil as well. If it is sandy or a type that tends to expand/contract more by season, you will want to plan your concrete foundation accordingly to give it the longest life possible.
• Make sure there is easy access to that area. Think about your driveway or walkway to your garage or shed. Ensure adequate space for building the garage or delivering the large prefab sections and the transportation vehicles. 

3. Prepare the Ground

• Remove all items that will hinder the placement of the concrete pad for your garage. To get you thinking, this includes roots, branches, brushes, small trees, and other materials. Once that is completed, you can begin marking the perimeter.

4. Measure Your Garage Pad

• The concrete pad for your garage must be the exact same size as your garage. For example, if your garage is 20×26, your concrete slab must also be 20×26. If you lay a foundation larger than your garage, water may run under your garage walls. Mark the corners and perimeter of your garage, making sure that it is square.

5. Excavate

• Next, you must determine what is level and dig accordingly. Excavate down about a foot below where you want the top of the shed pad to be, then dig out a trench around the perimeter for the footing and block wall. Site prep specifies that the footer base is usually dug to 20” x 8” and about 36” below your final grade; however, this may vary according to your municipality’s guidelines. 
• Check that it is level the whole way around. 

6. Pour the Footings

• And add number four rebar in the trench for reinforcement (usually determined by the municipality). 
• Prepare your concrete mix using the correct ratio of cement, sand, aggregates, and water. In most cases, your local concrete carrier will ensure that you receive the best concrete mixture. Finally, pour the concrete in the trench to the desired (required) depth and level. Once the concrete is hardened, lay the block wall. 

7. Lay Blocks

• On top of that concrete, you will lay three courses (or layers) of eight-inch blocks, keeping the wall straight and level. Site Prep recommends that the final layer be a six-inch block or a ledge block, which allows the concrete pad to be poured within the ledge. When laying the blocks for the footers, ensure that every section extends a minimum of two inches above the highest portion of your grade. 
• For extra reinforcement, fill the inside of the blocks with concrete and rebar about every six feet. 

8. Compact the Soil and Add Gravel

• Next, make sure that the soil in the center is compacted well. Then, lay 4-6 inches of gravel. As with a stone shed pad, use larger crushed clean stone. This gravel is imperative for many reasons. First, gravel prevents water accumulation beneath the concrete. Second, it acts as a barrier, protecting against soil erosion. Lastly, gravel creates an extra layer of support beneath your concrete slab, ensuring longevity for your garage. 
• Compact the gravel and use a laser level to ensure that it is level according to your garage’s grade.

9. Add Moisture Barrier and Reinforcement

• Usually, you will want to lay a moisture barrier and another layer of reinforcement, such as a fiber or wire mesh. You can also add a material into the concrete mixture to make sure it is strong enough

10. Pour Concrete Foundation

• Finally, pour the concrete mixture and spread evenly as you go. You should be pouring a minimum of 4 inches of concrete. Smooth the concrete surface.
• If required, install anchors for the building.
• It is a good idea to cut an expansion joint to control cracking.
• Power trowls are helpful to create an especially smooth surface.
• Let it Cure! This will take up to four weeks, though you may be able to start construction before then. Here’s an article about speeding the process and some dos and don’ts.

11. Remove Formwork

• Some foundation types or contractors prefer to lay a formwork barrier around the edge before beginning the process. If this was done, remove it, and fill the dirt back in around the exterior. 

12. Seal the Concrete (recommended but not required)

13. Grade the Site

• Grading the site can happen before the concrete foundation is finished, but spread the excavated soil evenly around the site and take care of landscaping that is needed. Perhaps plant some grass in the disturbed area, or cut a flower bed for use.

Some steps and info taken from Site Prep, Jamaica Cottage Shop.

What is the Best Foundation for A Garage?

Concrete foundations are popular for garages and large sheds for several reasons. 

Durable

Concrete pads are the most durable type of foundation, made with materials highly resistant to erosion, water, and infestation. This makes their likely-hood of water damage, drainage issues, and maintenance needs the lowest.

Sturdy

Compared to other foundation types, concrete foundations are best able to bear the weight of larger buildings and withstand the wear and tear of vehicle usage without breaking down or settling.

Long – Lasting

Because of their exceptional durability and resistance to the effects of nature, one can utilize concrete foundations with long – term intentions. The longer the life-span of the foundation, the longer your building will last.

Is it kinda an overkill? Check out our Garage Pad Installation services; get both the shed pad and the shed delivered and installed the same day!

Common Concrete Garage Foundation Questions

1. How deep should a concrete base be for a garage?

It depends largely on the dimensions of your garage and also what your municipality requires. It should be a bare minimum of 4-5 inches. 

2. Are footings required for a concrete garage foundation?

Not necessarily if your foundation sits on good, solid, level soil. However, they might be required if your local codes require them for your type of foundation and the size of your garage.

3. Can I pour a concrete foundation directly onto dirt? 

This might be possible for very small concrete slabs, like a small shed, if the ground is very compact. But generally speaking, this is a bad idea for a couple of reasons.

• Dirt is not stable enough, and your concrete foundation will tend to settle or crack more quickly, shortening its longevity. 
• Without proper drainage, water will tend to collect and erode out the bottom of your foundation.

It’s advised to put gravel under your shed. In some cases, local building codes require a certain amount of reinforcement or footings in your foundation plans.

4. How large should the garage concrete pad be?

Build the garage concrete pad EXACTLY the same size of the garage which you have purchased or plan to purchase. Please do not go larger than the building or there could be problems with water flowing under the wall! If you fail to follow these directions, Sheds Unlimited is not responsible for leakage that might occur.

5. How much does a concrete garage foundation cost?

According to Angi.com, for a more easily constructed foundation, you will pay from $5-$16 per square foot or (approx. $5,000-$21,000). If you are getting a basement included in the foundation or planning for a heavier-duty concrete foundation, your costs will obviously be higher. Additionally, you will need to add the costs of labor, materials, building and zoning permits, and soil testing. Read more on the breakdowns of foundation costs.

6. Should you build a concrete garage foundation yourself?

You can. It is definitely not impossible to install your own concrete foundation (especially if it is small) if your skill level allows it. It can make the project much cheaper. That being said, it may be much easier in the long run to get a local contractor to do it. They will be aware of what is needed to make your foundation durable and long-lasting and what your local requirements might be. They will be familiar with the process of receiving inspections and permits for your foundation project. Contractors can complete your foundation in a day or two, while it might take you a couple of weeks. Your building is only as good as your foundation! 

7. Anchoring Your Garage to the Pad

You do not need to install anchors into the garage pad unless your local town requires it. Sheds Unlimited will install a pressure-treated sill plate with 1/2 inch Wedge Anchors every 4’ around the perimeter of the building, excluding the doors. If a local town requires that the bolts be concreted into the foundation, please contact Sheds Unlimited at 717-442-3281

8. Do you need rebar for a 4” concrete slab?

Possibly not. If your slab is thin, use a wire mesh to reinforce the concrete instead. 

9. Where is a concrete foundation contractor near me?

If you live in PA, we have compiled a list of contractors that we (as shed and garage builders) would recommend.

Conclusion

If you are considering getting a garage or shed, we have prefab options that could be just for you. Sheds Unlimited specializes in custom prefab garages. We will custom-create your garage from single-car workshop garages to large 4-car two-story garages. Get a free quote, or just browse for your own inspiration. We have many completed jobs that you can look through to see what we do! 

Watch How Our Foundations and Garages Are Installed