When I was considering how to build the foundations for the shipping container, there was a lot to consider. How strong did they need to be?. What would be easy to build?. I built two sets of foundations as the containers started at a temporary development site, and were later moved to a permanent location. Here is some of the thought process.....
At the temporary site, I wanted a quick and inexpensive solution. At the final site, I wanted foundations I had confidence in.
I consulted widely, and came to realise that containers have been placed on many different foundations for different reasons. The quickest and easist was bessa blocks / cinder blocks / breeze blocks or cement blocks. My storage container is sat on pairs of blocks under the corner castings raised to a level height. The main house has purpose built foundations that took fair level of effort to build. Whilst I was researching what the "Correct" method of supporting a container was, I came upon a very large comercial building site. It was a small village of portacabins and was inhabitted by architects, construction engineers and building inspectors. The two pictures below are an axample of comercialy acceptable foundations on a major construction site.
I started with the pad the containers were going to sit upon. This is a gently sloping piece of ground that will drain water slowly away, and prevent it from becoming too wet. Even compacted and draining ground can become waterlogged, and a good thick layer of gravel prevents getting muddy feet in a downpour.
For the main container house foundations I considered the fiollowing: concrete blocks laid flat, blocks laid flat but cemented together, hollow blocks aranged in a square and filled with cement, cardboard tubes filled with cement, blastic barrels filled with cement, wooden poles sunk into the ground, shuttered and poured concrete foundations, railway sleepers, railway track laid out to allow multiple containers to share a level, a low cement block wall, a tall cement block wall and acro props cemented into the ground to create a foundation that could be leveled by turning a shaft collar.
I considered how I was going to anchor the container to the foundation. I considered embedding a metal plate onto the top of the foundation, this would allow me to weld the casting to the plate. I eventually opted to install threaded rods into the wet cement.
A container with no modification will remain rigid with a full cargo load on just four corner castings. If you make too many holes in the walls, the floor develops a spring or a bounce, and more support is required to prevent it from bouncing. I opted for only modest holes in the walls, and stuck to four corner foundations. When a house is being built, the builder identifies if the ground is soft or solid, and this determines the depth and size of the foundations. This is made more complex if the land is sloping.
You need to consider if the containers will be placed with a crane or a side loader, because a crane can lift to any height where as the side loaded is limited in how high it can lift the containers. For a container with no water connections, a low foundation works. If you want a shower or a toilet and you want the pipes to go down through the floor, you need to elevate the container to provide access to the pipework.
My living container has no water connections and remains close to the ground. I have enough clearance under the bathroom to easily install and service my plumbing.
Most of the work was in the preparation for the foundations.
If you are using concrete, you may want to consider having it delivered in one go, or mixing yourself in smaller quantities. The challenge with that was not having power, water or aggregate easily on site. Most of the work was in the preparation so that everything was square and level. I found a water level was more reliable than the fancy laser levels.
I cover the details and costs for both of my foundation costs in ebook 1, rather than this blog.