Do I Need A Foundation For My Shipping Containers?
In short, you will always need a foundation for your shipping container home. This is because the ground moves a considerable amount. The ground can rise, sink or slide. This movement can be sporadic and is usually very slow. Even though it is often barely noticeable, this slight movement can affect how level your home is.
A foundation provides a solid, stable platform for your building. Without this solid platform the ground’s natural movement can cause the containers to split and separate.
The ground underneath your building can also be comprised of different materials. For example, part of the ground could be hard rock and the other part soft clay. This creates an unevenness which can allow your home to shift since the load isn’t equally distributed. One result could be having doors that are incredibly difficult to open and close.
A solid, well built, foundation will ensure the weight is appropriately distributed. It will also help prevent moisture and the corrosion that occurs as a result of this moisture.
Note that if the shipping container home will be relocated within a few months, it is sufficient to use railroad ties for this short time frame.
Types of Shipping Container Home Foundations
The three main foundation types which can be used with container homes are pier, slab and strip. There are other types of foundations but these are the most commonly used with container homes.
We will outline when you should use each one and discuss the strengths and weaknesses for each.
Pier foundations are the most popular choice for shipping container homes for numerous reasons. They are relatively inexpensive, DIY friendly, and quick to construct.
As seen in the photo above, a pier foundation is comprised of concrete blocks. Each concrete block, or pier, is generally 50 cm X 50 cm X 50 cm.
With shipping container homes, the concrete piers are generally laid at each corner of the container. And, with the with larger 40-foot containers, an additional two piers are placed midway down each side of the container.
The pier foundation is a favorite among many DIY home builders because they are the simplest, cheapest and quickest foundation to lay. No special equipment or experience is necessary for laying a pier foundation.
You save a lot of time and money with pier foundations because you don’t need to excavate a lot of earth at all. You only need to excavate the ground for the piers, which are generally 50 cm X 50 cm X 50 cm.
Compare this to a slab foundation where you will need to excavate more than 18 feet x 18 feet.
Another great reason to use a pier foundation is that other foundations, such as pile foundations, require expensive specialized equipment which can obviously be difficult for DIY builders.
A slab foundation is a popular choice when the ground is soft and requires an equal weight distribution.
As shown in the photo above, a slab foundation is a concrete slab onto which your containers are placed. The slab foundation is generally slightly larger than the footprint of your home.
If you are building with two 40-foot shipping containers, your slab foundation would typically be 18 feet wide by 42 feet long. This would provide an overhanging foot of foundation around the perimeter of your shipping containers.
The slab foundation is generally used on softer soil types. Pier foundations place a great amount of load under a small surface area while slab foundations spread the load across a large surface area.
A huge benefit of slab foundations is that because it provides a solid base, there is no hollow space in the foundation. This prevents future problems such as termite infestations.
Unfortunately though, because of the additional concrete used and the vast amount of space which needs excavated, slab foundations are significantly more expensive than pier foundations.
Note that with slab foundations, once the concrete has set, there is a lack of access to utility lines. If you have a leak in your water pipe, the concrete will have to be cut to access the pipe. With a pier foundation, you will always have access to your utility lines.
A strip foundation (also known as a trench foundation) is somewhat of a combination of the previously mentioned pier and slab foundation.
The strip foundation, shown below, is simply a strip of concrete which is laid to support the containers. The concrete strip is normally 1-2 feet wide and 4 feet deep.
The strip can either go around the perimeter of the containers or it can be laid at the top and bottom of the containers instead.
It is ideal to use when you’re looking for a cheaper alternative to the slab foundation but have slightly less firm ground to lay the foundation on.
For locations where the ground stays damp much of the time because of large amounts of rain, a rubble strip foundation using loose stone below the concrete strip can be used. This stone allows the water to run through and drain away.
Like all the foundation types mentioned, strip foundations also have their weaknesses. For instance, strip foundations have a weak resistance to wind and earthquakes. Also, due to their shallow form, strip foundations are best suited for small and medium-sized builds.
How to Attach Shipping Containers to Foundations
The most popular way to attach containers to the foundation pad is through a steel plate. While the concrete is still curing, a steel plate with vertical bars is set that sinks into the wet concrete.
Paul Chamber’s video shows an excellent example of this.
Once the concrete has cured, the shipping containers can be placed on the steel plate and welded together.
Optionally, if you don’t want to use the steel plate technique, you can bolt the containers down into the concrete using concrete anchors. This is a simpler technique, but the hold isn’t as strong as welding the containers.
Finally, if you are opposed to permanently attaching the containers to the foundation, you can just place the containers onto the foundations. You sacrifice some additional strength when you choose this route.
The only exception to the suggestion of permanently attaching the container to the foundation would be if the container is being built to be portable.
This article discussed several most typical types of foundations used in shipping container homes, but not all types of foundations. There are other types of foundations, including the pile foundation used in the Graceville Container home.
We made our selection of foundation types based on those that are most commonly used and the most DIY friendly, since many of you reading this article are self-builders!
Our recommendation is that you attach your shipping container to a foundation which will add extra strength to your building.
We welcome your questions. Send them to us using the comments section below.