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5 Types of Foundation for Garages, Carports, and Sheds

contractor installing wood foundation beams on floor

Most buildings need a strong and solid foundation. Not only does a good foundation help keep your building in place, but it also helps protect against flooding and costly repairs. As a vital component for the structural integrity of your building, it’s almost as important as the structure itself.

There are different types of foundation for different buildings and sizes. While the type depends heavily on your plans for using the space, other factors like climate and geographical location also play a role in the ideal foundation.

In this article, we’ll explore a few types of foundation to consider for your building, the benefits of each, and which is best for your construction project.

Common Types of Foundation

While there are several types of foundation in construction, no two are alike. Each variation has its own pros and cons, meaning there isn’t a one-size-fits-all option. Below, we’ll explore five of the most common for metal structures, such as garages, sheds, and carports, and recommendations for each type of building.

Poured Concrete Slab

animation of poured concrete slab foundation

Also known as “slab-on-grade” foundations and “monolithic” concrete pads, these are flat slabs of concrete poured into one single piece on the ground. Newly poured concrete takes about twenty-eight days to fully cure, however it’s strong enough to start framing about a week after installation.

This type foundation is a simple and fairly quick installation process when done correctly. Concrete is also fire and termite-resistant, making it a long-lasting and reliable option.

Poured concrete slabs are one of the most common choices for houses because they are low-cost and durable. These advantages make it the preferable base for parking vehicles—recommended for carports and garages.

On the other hand, concrete slabs are not ideal for climates where the ground can freeze and thaw, which can cause the slabs to crack and shift. Additionally, you’ll have to handle sewage and drainage pipes before slab installation, since you’ll have to cut into the slab to fix them if problems arise.

The average concrete slab has a thickness of four to eight inches, depending on your local building codes. For heavier vehicles, such as for parking RVs, requirements for slabs may be up to six inches thick.

Concrete slab specs to know:

  • Thickness: At least four inches, suitable for most garages.
  • Size: Recommended twelve inches wider and twelve inches longer than the base of the garage, varies by location, use our concrete pad size calculator to determine right size for property.
  • Slope: Should be completely level, especially for detached garages.
  • Edges: Recommended to slope the outer edges of the pad three-fourths of an inch lower than the top of the pad to prevent rain water from pooling.
  • Footings: Must be thicker than the remainder of slab to support garage walls, usually required one foot deep and one foot wide.

Wood

animation of hammering wood flooring installation

Wood may not be as strong as solid concrete but it carries other qualities that make it a reputable foundation choice. While regular wood is prone to termites, mold, and decay, the preservative agents in pressure-treated lumber, such as chromated copper arsenate (CCA) can withstand them all. 

Pressure-treated wood foundations became popular around the 1960s, where the beams are generally placed on gravel or atop concrete masonry blocks to create crawl space. What’s notable about wood foundation is its quick and simple installation process, which is fairly easy for a woodworker or DIY enthusiast. 

Wood is also a natural insulator, helping keep the interior structure warm and less drafts in crawl spaces. Buildings with a wood foundation consume less energy than those with concrete base, making them ideal for spaces where you plan to spend a lot of time, like workshops.

The downside is that wood foundations tend to cost more than poured concrete, considering the amount of lumber needed. It can also be toxic during installation due to the preservatives, and unfortunately is still susceptible to rot and insect damage if not properly treated.

Certain wood types, including redwood, cedar, and cypress are naturally resistant to mold and insects, but they’re more expensive. Wood foundation also requires well-maintained dry soil, so damp and humid areas aren’t ideal.

Wood foundation specs to know:

  • Preservation: foundation-grade pressure treatment, damp-proofing, spacing for good drainage.
  • Footing: posts on solid pea gravel or concrete blocks 16x8x2 in. 
  • Size: 4×4-in. lumber runners.
  • Stability: proper fasteners, durable studs for soil pressure, post base brackets, nails to secure panels to frames.

Gravel

animation of maintaining gravel foundation

For portable metal buildings like mobile homes, gravel foundations are a great option. They’re also the best choice for sheds, allowing you to move or relocate it as desired.

The perks of gravel is that it’s the most affordable and readily available foundation type. Also, water drains quicker through gravel than soil and other types of foundation, making it an ideal shed foundation. With gravel, you can create better leveling, and it’s an easy DIY installation.

With that said, gravel isn’t as durable or strong as other foundation types. Gravel foundations also require mobile home anchors for carports, which may require drills and professional help to secure firmly. 

Last but not least, gravel foundation may need frequent maintenance, which is why many people choose to frame it with timber around the base. This helps keep the gravel inside and can look nicer for yards and gardens. 

Gravel foundation specs to know:

  • Type: Three-fourth inch stone, aka 57 Granite, Crusher Run (mix of ¾” and smaller), three-fourth inch bluestone for wet areas
  • Size: Two feet wider and Two feet longer than size of shed or storage building
  • Thickness: Four to six inches or more for better drainage

Pier and Beam

animation of installing pier and beam foundation for building

Also known as “pier and post,” this foundation is popularly used in coastal areas and those prone to hurricanes. This is because piers elevate your building, providing structural support in case of flooding. You may recognize homes with this type of foundation as  “stilt houses.”

Pier and post foundations are composed of three main elements: 

  • The posts (or “piles”)
  • Wooden beams
  • Concrete piers installed deep in the ground.

This foundation type is good for anchoring large storage buildings above soil that constantly floods and shifts.

Not only do piers and posts protect structures from water damage, but they also prevent them from sinking. You’ll automatically have ample crawl space beneath this foundation, creating easy access to wiring and pipes. Another perk is the flexibility to build on uneven land. In the event of damage, they’re easier and cheaper to repair.

As for the cons, pier and post foundations require professional planning from a structural engineer, to ensure proper installment. This makes them a bit more expensive than concrete slabs. Additionally, the space beneath piers is susceptible to animal and insect infestation, which can be problematic in certain regions.

Pier and Beam specs to know:

  • Size: 8×8 in. or 12×12 in. concrete blocks, 6×6 in. treated wood posts (foundation grade)
  • Footing: reinforced concrete on firm undisturbed soil and level, at least twelve inches diameter, at least eight inches thick
  • Spacing: about 18–22 inches high/crawl space

Concrete Masonry Units (CMU)

animation of laying concrete masonry units

Last of all are concrete masonry units (CMUs). Also known as large cinder blocks,  CMUs are held in place with mortar as another type of foundation. They’re a great option for commercial buildings, such as warehouses, especially if you’d like to add a basement for additional storage. 

This is because CMUs have great compressive or “load-bearing” strength. Cinder blocks are low cost, sustainable, and low maintenance. Also, just as with poured concrete slab, CMUs are fire- and insect-resistant, and readily available.

As for drawbacks, CMU foundations are not well insulated. They can be heavy to handle, so you’ll most likely need a professional company to help install them. More importantly, these blocks aren’t water-resistant, which can lead to expensive repairs down the road.

CMU foundation specs to know:

  • Size: 8x8x16 in. concrete blocks or larger
  • Stability: vertical reinforcing bar (rebar) in holes filled with concrete
  • Footings: cast-in-place concrete on undisturbed soil, beneath frost depth

Factors When Choosing a Foundation 

To select the best type of foundation for your project, there are a few factors to consider beforehand:

Intended Use 

How do you plan to use your building? Even a simple shed to store garden tools will most likely have construction regulations for the foundation. You’ll first need to check the local building codes and HOA guidelines of permits, frost lines, and location specs on your property, as well as underground utilities. 

Size and Space 

Next, the building’s dimensions, including its horizontal and vertical load, must be taken into account. A good rule of thumb is to have at least three feet of clearance around the perimeter of sheds—and even more for garages and storage buildings—to ensure enough space between fences and other structures.

Climate

The local climate, including moisture levels, weather, and wind conditions, will also affect your foundation choice. For example, concrete slabs can crack under pressure in colder regions that freeze and thaw at different times of the year.

Soil and Landscape

Lastly, you’ll want to build on an area that is close to level and doesn’t collect water. It’s best to test the quality of the soil, such as its moisture content and settlement, to determine if it supports your foundation of choice.

Frequently Asked Questions

What is the difference between shallow and deep foundations? 

Foundations are divided into two separate categories: shallow and deep. These terms refer to the depth at which it’s placed in soil—shallow foundations are for lightweight buildings and are more affordable than deep foundations.

What is the most affordable foundation type?

Concrete slabs are considered the cheapest foundation for homes and garages, which typically cost $8–$15 per square foot. However, for smaller structures like sheds, gravel foundations are cheaper at around $1.25–$1.50 per square foot. 

Which foundation is best for a shed?

Since it’ll most likely be for garden supplies, mowers, and household items, gravel foundation is best for sheds. Not only is gravel cheaper than a concrete slab, but it also promotes water drainage, protecting your storage items from water damage.

What is the difference between footing and foundation?

The footing is a portion of the foundation that actually touches the soil, providing support to the rest of the foundation from underneath and creating a safe settlement. Simply put, think of the foundation of your building as the “legs,” and the footing as the “feet.”

Design Your Next Building on a Strong Foundation

Even with a strong and stable foundation, problems can still arise if your building is improperly assembled or installed. Using our 3D Customizing Tool below, you can easily design and purchase your dream structure. Once purchased, our skilled team will deliver and install your custom building for free.

Get an instant price for your new carport or metal garage.

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Alan Bernau Jr

Alan Bernau Jr. is the founder and owner of Alan’s Factory Outlet. He has helped more than 50,000 homeowners design and install custom carports and garages over the last 20 years.

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