Metal Garage Foundations 101: Concrete Slab, Gravel, Or Dirt?

So, you have decided to install a brand new metal garage on your property. You start choosing your dream design and all customizations for optimal functionality and aesthetic appeal. But, there is one more, super important step that you must not forget to include in this preparation – a metal garage foundation.

A strong foundation is what will determine the strength and durability of your garage building. Without it, the ground can shift, which will lead to cracks, rust, and structural damage over time. So, choosing the right foundation is highly necessary for a long-lasting garage. But which foundation works best with a steel garage?

• Concrete slab
• Gravel bed, or
• Dirt base

In this blog, we will break down each of these three popular options, pros and cons, how deep each must be, respective anchors, and which one is best for you. Let’s start!

I. Concrete Slab Foundation For Metal Parking Garage [Best Choice]

Check out in-depth details on a concrete slab for a steel parking structure and learn about its features.

What Is A Concrete Slab Foundation?

It is a strong, solid base made by pouring concrete over the ground. Sometimes, reinforcements like steel rebar are added inside wet concrete to make it even stronger and crack-proof. It does not move or shift with time, making it one of the best metal building foundation options for year-round use.

Benefits Of Concrete Slab For Steel Prefab Garages

• It is a strongest foundation and best for heavy load bearing like cars, tractors, or business storage.
• It is water resistant, which keeps water, pests, and rot away while protecting your garage and stored items.
• It is versatile and works for all sizes, from steel outdoor sheds to metal commercial buildings.
• A concrete base helps keep the interior dry and clean and is suitable for storage and workshops.

Cons Of A Concrete Base Slab

• It has a high initial cost compared to other types of metal structure bases.
• It is more labor-intensive as land owners must prepare the site, set forms, pour concrete, and wait for at least 28 days for it to cure fully.
• Concrete is not permeable, so it requires proper drainage to avoid waterlogging around the slab.
• Once it is set, it is harder to modify, remove, or change.

What Anchors Can You Use With A Concrete Slab For Metal Building Installation? 

Steel frames must be attached to the concrete foundation with the help of correct anchors, such as:

• Anchor Bolts: These are J-bolts or L-bolts, inserted in wet concrete before leaving it to set.
• Expansion Anchors: These are drilled into cured concrete, which expands tightly inside the hole when tightened.
• Sleeve Anchors: These are strong fasteners and are used for heavy loads to help secure the base rail in place.

At Carports Advisor, we provide additional concrete brackets to maximize the stability of the steel frame garage. You can check it out with our free and easy-to-use 3D designing tool for creating a metal parking garage from scratch.

How Deep Should A Concrete Slab Be?

• Standard Thickness: 4 to 6 inches for most metal structures.
• Heavy-Duty Garages: Up to 8 inches’ thickness for a large metal repair building or storing heavy equipment.
• Sub-Base Matters: A layer of compacted gravel underneath the concrete slab helps with drainage and stability.
• Cold Climate Considerations: Deep footings below the frost lines to prevent cracks.

When To Choose A Concrete Base For A Steel Building?

You can choose a concrete base for:

• Home garages
• Workshops
• Commercial use
• Long-term farm storage
• Industrial use
• Living space

II. Gravel Base For Steel Garage [Budget-Friendly]

Let’s see the details about the grave base for metal loafing sheds and garages:

What Is A Gravel Foundation?

It is a layer of compacted gravel that creates a leveled surface for metal structure installation. It’s simple, affordable, and offers better drainage than dirt. It works best for the semi-permanent type of steel structure setup for stability.

Pros Of Gravel Steel Building Foundation

• It costs less than concrete and is a budget-friendly option.
• It offers great drainage as water flows through the gravel instead of pooling.
• You can DIY as it is easy to install and does not require sophisticated tools and machinery. Just level the ground and compact it.
• It can be adjusted or moved when needed, making it flexible.

We suggest considering the weather while selecting the foundation along with soil types, size of the metal prefab building, and its purpose.

Cons Of Gravel Steel Building Foundation

• It is not as solid as concrete, so heavy load-bearing may shift the gravel base over time.
• Gravel can move or settle, so it requires occasional maintenance.
• It is not ideal for a dust-free, dry, and clean space for a workshop, office, or warehousing.

What Anchors Are Best For Gravel Base?

You can pick the following anchors for a gravel foundation:

• Ground Anchors (Auger Anchors): These are large screws that are drilled deep into the ground to hold the steel frames steady.
• Deadman Anchors: Heavy objects are buried beneath the gravel to give a strong anchoring point to the steel building.
• Concrete Footers: Here, concrete blocks are added below the key sections to improve grip and avoid shifting.

What Should Be The Depth Of The Gravel Foundation For A Steel Garage?

• Standard Depth: 4 to 6 inches for compact gravel (for a stable base).
• Crushed Rock Base: You can add crushed rock underneath the gravel bed for extra strength.
• Leveling: You must properly level the surface before installation to keep the garage frame sturdy.

When To Choose A Gravel Foundation For Your Steel Parking Building?

The best use of a gravel bed foundation is for:

• Farm and business storage (where drainage is a priority)
• Semi-permanent structures that may change later on
• Budget-conscious buyers who want an easy DIY option

Note: The durability of the gravel base is high, but it will need occasional re-leveling to maintain an even surface. Though it is durable, it is not as stable as concrete, especially during extreme weather events.

III. Dirt Foundation For Metal Prefab Garage [Least Recommended]

Let’s learn about dirt foundation used as a base for installing steel prefab garages, along with its pros and cons, and types of anchors that you can use.

What Is A Dirt Foundation?

A dirt foundation is simply a leveled ground for steel garage installation. It has no installation cost, which makes it the most affordable option of all three. But dirt can sink and shift, and is not very stable. It is mostly used for temporary setups when a solid base isn’t required for long-term use.

Pros Of Dirt Steel Structure Foundation

• You don’t need to buy material for a dirt foundation setup, making it most affordable.
• It can be done quickly as you don’t need a special setup. Just level the ground, and you are good to go.
• It can be upgraded to a gravel base directly for extra stability.

Cons Of Dirt Steel Structure Foundation

• Dirt can move around easily, leading to shifting, sinking, and uneven flooring.
• Since there is no solid base, water can soak through, causing rust and mildew, especially on stored items.
• Bugs, insects, and rodents can easily enter since the floor is unsealed.
• It is not suitable for most use and not recommended for permanent structures, workshops, or places where stability is of prime importance.
• It is prone to risk in windy areas as anchors can move.

What Anchors Are Best For Dirt Base?

The best anchors for a dirt foundation are:

• Ground Anchors (Auger Anchors): It can be screwed to the dirt to help hold the garage in place.
• Concrete Piers: They can improve stability, but add to the total costs.

Dirt base has limited reliability as anchoring dirt is weaker than other foundations, which makes it less dependable during bad weather.

What Should Be The Depth Of The Dirt Foundation For A Metal Prefab Garage?

• No actual depth required
• Compacting can make the base more stable

Tip: Mobile home anchors (helical earth anchors) can be screwed into dirt for extra hold. If you can stretch your budget, add concrete piers for more support and stability. You must know different types of structural loads on steel structures before choosing the depth and foundation type.

When To Choose A Dirt Foundation For Your Steel Prefab Building?

• You can opt for a dirt foundation for the following:
• For storing temporary garages (that are not needed in the long term)
• Seasonal farm storage (for hay bales and harvesting tools)
• Buyers with a tight budget

Note: Since dirt foundations don’t offer much support, they work best only for short-term use. In the long term, it can cause serious garage shifts with time, structural instability, and frequent damage and repairs.

How To Choose Which Foundation Is Right For Your Steel Garage Building?

Have a quick look at what factors affect the selection of a steel prefab garage foundation in the table below. However, before that, we must remind you that it is best to avoid crucial mistakes when installing steel buildings, including pouring foundation before getting plans and securing a permit.

Factors	Concrete Slab	Gravel Bed	Dirt Base
Budget	High upfront cost Last longer	Lower cost Needs releveling	Most affordable Costly problems later
Intent of Use	Workshops Vehicle storages Heavy equipment	Storage Semi-permanent garages	Temporary/ Seasonal use
Garage Size	Generally, all types Suitable for Large	Medium-sized	Any temporary building
Load Bearing Needed	Heavy load bearing	Moderate weight	Lightweight structures
Local Climate	All weather Needs better drainage	Allows water drainage Needs timely adjustments	Can flood Become muddy Causes moisture damage
Permit Requirement	Yes	May requires proper anchoring	May not meet building codes in some areas
Recommendation	For long-term durability, low upkeep, and stability	Alternative for budget-conscious buyers	Not recommended for most garages since unstable

Concrete, Gravel, Or Dirt? Pick The Right Metal Garage Base Now! 

So, which foundation will work best for you? A concrete slab is a strong and long-lasting option for a permanent garage but comes with high initial costs and a long curing time, while a gravel base is affordable and gives a semi-permanent solution, and dirt is the cheapest but least stable choice.

Note that the foundation choice depends on your budget, climate, garage size, how long you want it to last, and what you are going to use it for. Need any expert advice? Call Carports Advisor at (336)-914-1654 to find your metal ‘dream’ garage for your home, farm, and business!