Choosing a foundation for container homes is no easy feat. Many things come into play such as the soil type, temperature, cost, the ground’s natural movement, and much more. Plus, is it even necessary to have a foundation for your shipping container home or business? That’s what we’ll cover below.
Shipping containers are helpful for more than just transporting cargo. With a few simple modifications, they can also make significant standalone structures. Just ask the thousands of people who have begun converting them into customizable, readymade homes.
There’s a world of difference between shipping containers and conventional edifices, so if you’re thinking about turning one into a living space, mobile office, or portable storage unit, it’s essential to do your homework. One of the first things you should look into is whether or not to use an underlying foundation to support and stabilize your container.
While there are no hard and fast rules for shipping container foundations, starting with a solid understanding of the where what, and why of your project will help you figure which type of foundation best suits your needs—if indeed you need one at all.
Do I Need a Foundation for My Shipping Container Home?
Before you can answer that question, you’ll first need to answer a few other preliminary questions. Namely, where you’re going to put your container and how long it’s going to be there.
The character of the soil at your intended placement site is the number one factor determining whether or not a foundation will be necessary.
As a general rule, you can get away without a foundation if the ground you’ll be placing your container on is level, stable, and dry.
If, however, you’ll be situating your container somewhere with overly wet or clay soil, a strong foundation is a must to prevent sinking, shifting, and other stability issues, as well as rusting and moisture-related deterioration.
Length of Time and Number of Containers
Another thing you’ll need to think about is how many containers you’ll be working with and how long you’ll be keeping them in place.
Less Than a Month
If you’re only going to be setting up a container temporarily, as is commonly the case with construction jobs and large-scale moving projects, there’s no need to lay a foundation. It’s improbable that anything would happen to the container in such a brief period to justify the time, labor, and expense associated with doing so.
More Than a Month
Assuming you’re planning on leaving your container where it is for longer than a few weeks, a foundation is a good idea. A semi-permanent foundation, such as a gravel pad, may be sufficient for sites that will be in use for up to about a year. For anything longer than that, you’ll want to commit to a permanent foundation.
Large structures that incorporate more than a single container will always require a foundation. Such structures’ added size and weight make them prone to sinking and shifting, even on firm terrain. And the bigger and more complex the structure, the more frustrating—and expensive—complications arising from structural issues can be.
Types of Shipping Container Foundations
Once you have a general understanding of shipping container foundation requirements, your next step will be to choose the type of foundation that best fits your own proposed setup, building site, and budget.
Shipping container foundations generally come in four main foundation types: pier, pile, slab, and strip.
A concrete pier foundation consists of square blocks of steel-reinforced concrete which are placed under each of the container’s four corner castings. Concrete piers elevate the container off the ground and ensure that it remains stable and level regardless of the condition of the surrounding terrain.
Since pier foundations are economical, easy to install, and require minimal excavation, they’re arguably the best foundation for shipping container homes. If you decide that you need some sort of basic foundation for your shipping container, a pier foundation will most likely be your best bet.
Pile foundations derive their unparalleled security from solid-steel piles, which are driven into the ground vertically and capped with concrete blocks to create an unshakeable platform with deep subterranean “roots.”
Pile foundations lie on the opposite end of the spectrum from pier foundations. They’re difficult to plan and expensive to install, and putting them in place involves specialized equipment and a considerable amount of technical expertise.
The upshot is that pile foundations are incredibly durable and long-lasting, especially on soft or wet ground. As such, they’re recommended for those looking to establish a foundation for a shipping container shed or similar building on land where an ordinary foundation just won’t cut it.
Concrete Slab Foundation
With a concrete slab foundation, make use of the same kind of thick concrete pads used to uphold traditional homes.
Needless to say, they provide excellent support and balanced weight distribution for both single and multiple containers on a variety of soil types. They also serve as an effective barrier against pests since they gird the underside of the structure with several feet of solid concrete.
Containers with a strip foundation, or trench foundation, offer a practical compromise between the ease and affordability of pier foundations and the sturdiness of slab foundations.
Rather than propping the corners of the container up on blocks, strip foundations rely on linear strips of concrete (essentially sunken walls) to bolster small and medium-sized structures. These strips typically run along the structure’s outer perimeter, though they can also be placed at either end of the container.
Concrete footings are the middle-range option for a container foundation. This container foundation takes more time and attention to construct, but is cost-effective, durable, and long-lasting.
To start building the concrete footing foundation for your container, you need to determine how deep the footing should be. This decision may not be necessary if you live in an area without frost. Nevertheless, if the ground freezes, it could cause your foundation to shift and cause problems in the future. You should always build your footing at least 6″ below the frost line, which varies from 50″ in North Dakota and 0″ in Florida. The National Snow and Ice Data Center can give you information regarding the frost line in your area.
Next, you need to choose the required footing dimensions. The chart below offers suggestions on how large your footings should be for one or two stacked 40′ ISO containers (not including the extended frost footing).
The process should begin at the highest point of the four corners. Compact the soil in the bottom of an area that is slightly wider and deeper than the footing requires. Build a concrete form with plywood and planks according to the dimensions chosen earlier. Add a 3″ base of loose stone.
The form should be assembled with screws if it will be reused for each footing. This will make the process of disassembling it for reassembling easier. Laying out the footings properly is crucial to the success of this project, and the first footing serves as the base for all other footings.
You should also add rebar to your footings to increase their strength and prevent them from cracking. In order for the rebar to be flush with the top of the footing form, it should be 8 inches longer than the depth of the hole. Every footing should have a few inches of rebar spaced a few inches apart, and the amount of rebar depends on how large it is.
Based on the height of the first footing, the next one must be measured and placed. For accurate height measurement, a laser level is necessary. After you’ve lined up the proper heights and distances, you’re ready to pour the final three footers or more, if you want to add security. Until all footers are in place, repeat the digging and installing of the concrete form and pouring of the concrete until the area is level.
Ideally, this should be done several weeks before the arrival of the container. It is best to consult a professional about the appropriate time for the concrete to cure depending on the heat and humidity in your area.
Surefoot Concrete Free Footing System
With its innovative steel footing, Surefoot delivers the ultimate uplift prevention for any type of foundation work. The slab footing is superior to conventional concrete slab footings in terms of load capacity and ease of installation.
Your container/s can be erected quickly by using refined geotechnical data and a design capacity calculated by the working stress method. The Surefoot has the advantages of enhanced stability as well as minimal disturbance to the soil and substrate. With both tested and certified performance in cyclone-prone areas, the Surefoot assures your construction project is built, fastened, and able to resist environmental challenges.
Wooden Beam Footing
As an alternative to concrete footings and creating concrete slabs, wooden beam footings are suitable for almost all soil types. Before your container is delivered, you can easily install these wooden beam footings. Several materials are readily available, including treated 4″ x 4″ wood beams (or railroad sleepers) and loose stone or gravel.
In order to erect the four corners of the container (if you are building with a single container), you will need to install beams at the four corners of the construction site. In most cases, the frame of the container is sufficient to support the floor and you need not add any additional support underneath; however, if pressure points are noticeable, you might want to add more beam footings under those points. Your beams will not rot because the gravel bed drains away moisture.
Additionally, beam footings are commonly used in high-flood areas when the property needs to be built on an elevated platform, giving flood water room to drain underneath.
Attaching Shipping Containers to Foundations
Regardless of which style of foundation you ultimately end up going with, it’s crucial that you have some means of securing your container to its new perch. Otherwise, it could still be uprooted by floods, tornadoes, hurricanes, or other natural events.
In most cases, you can accomplish this by fastening the container to one or more steel plates.
Be sure to use plates that are welded with high-strength concrete anchors and press them into the concrete while it’s still wet so that the two surfaces have a chance to bond fully. With the right tools, it’s also possible to bolt steel plates to a concrete foundation after it’s dried.
Choosing the Right Concrete for Your Foundation
The kind of standard-strength, all-purpose concrete mixes you find at home improvement centers have a C value of around 20-25. Most builders use C20 concrete to pour slabs for houses, which means these garden variety mixes will be more than strong enough to support even a multiple-container arrangement.
The only circumstances under which it might be advisable to use a special grade of concrete are if you live in a region where extreme weather conditions are common or you’re placing your container on an existing foundation that’s had integrity issues in the past.
Working With Concrete in Hot Weather
Concrete mixes, pours, and cures most efficiently when it’s kept at a consistently moderate temperature. If it’s especially hot out, a few precautions will be in order to ensure the success of your project.
While your concrete is mixing, spray your entire worksite and surrounding area thoroughly with a hose. Wetting the ground will serve not only to cool it off but also to soften it, improving the concrete’s ability to hold.
Working With Concrete in Cold Weather
Like excess heat, frigid temperatures can also negatively impact the workability and ultimate strength of newly-poured concrete.
Before laying concrete in below-freezing conditions, first do away with any ice, frost, or standing water that’s found its way onto your worksite. Excess water, even in solid form, can interfere with the texture of the finished concrete. If not dealt with, it can lead to curing inconsistencies and even crumbling.
Every building needs a strong foundation. This is no less true for ones made from shipping containers.
By taking the time to explore your options and selecting the right type of foundation for your particular arrangement, you can all but guarantee that your container—or container-turned-dedicated-structure—will stay put and fulfill its designated purpose week after week, month after month, or year after year.