Why shipping container homes need a foundation

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Shipping contains are originally designed as structurally strong modules, that can be stacked up to 9 stories on a ship. Then why do they need a foundation? The simple answer is that the ground is not as stable as a ship deck. To completely understand the reasons as to why the structurally strong shipping containers might need foundations, we must understand what the role of the foundation in a building is.  

Shipping container homes need a foundation in most cases. The long exposure of weight on the ground tends to push the soil downwards and the structure can start to sink. The foundation acts as an anchor and prevents the structure above it to sink or getting unstable due to any movement in the soil beneath it. 

If a temporary or short-term solution is needed, there are some possibilities for that as well. It’s explained in the second last section of this article. 

How do foundations facilitate a shipping container home?

Foundations play the following important roles in a shipping container home.

  • To prevent the container to sink or getting unstable or unleveled with the soil.

Even though shipping containers have a flat base, they need flat ground to function efficiently. Even a minor discrepancy in the level can mess up the plumbing system and lead to improper functioning. It could cause hindrance in water supply and collection of wastewaters in corners of the pipelines due to the crookedness that could eventually lead to health and sanitary issues.

  • To allow the space for plumbing beneath it

Placing the shipping container on the foundation also allows some space beneath the container to suspend the central sewage line. It is the most efficient way to layout the plumbing system without much hassle.

When can a foundation for shipping container homes be avoided?

These are the conditions when avoiding or eliminating a foundation might be the right choice.

  • It is a temporary placed single container home: 

If your container home is a single container tiny home, and you intend to keep it mobile or move it to a different location after a few months, then it might be beneficial to save the foundation costs. Shipping containers are structurally stable and can stand stable on the ground on their own, as long as the soil movement beneath it is minimum.

For this reason, shipping containers make excellent modules for temporary and emergency housing in disaster-struck areas.

  • If the ground below is of a stable soil type or hard rock:

In rare cases, it is possible that your site is made up of type A soil, which has a large concentration of loamy soil and is relatively stable for long periods of time, or flat hard rock. In such cases, if the container can stand levelled and horizontal, then the foundation can be eliminated.

Types of Foundations for a Shipping Container Home

The following list of foundations is the most suitable foundations for Shipping container homes. The selection of the type and design of the foundation depends largely on the soil type on the site.

Pier Foundation:

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This is the most popular type of foundation for Shipping container homes. Each pier is generally 50 cm X 50 cm X 50 cm and contains reinforcing steel inside to improve the concretes strength in tension. There are various advantages of this type of foundations

Pros:

  • Saves a lot of money and material
  • Only needed at our corners in a 20 ft container, and two extra in the middle for a 40 ft container
  • Quick to construct
  • Needs only 50 x 50 x 50 cm of excavation per pier.

Cons:

  • This type of foundation works only if the soil is a little bit stable. For very loose or marshy soils, other stronger and more stable types of foundation need to be used.

Slab Foundation

A slab foundation is a popular choice when the ground is soft and requires an equal weight distribution. It is basically a reinforced concrete slab a little larger (2 feet wider both ways) than the footprint of the house, to provide for a stable and levelled ground for the container home. It provides an overhanging foot at the perimeter of the container.

Pros:

  • Stabilizes the soft ground.
  • Avoids any termite or other infestations in the future as it has no hollow space within.

Cons:

  • Increase the potential for heat loss when ground temperatures drop below the interior temperature because the container can conduct heat into the ground, which transfers more heat than via convection into the air.
  • Expensive, as it needs a lot of excavation and large quantities of concrete and steel
  • Time-consuming

Strip foundation:

A strip foundation is another popular type of foundation, often used as a cheaper alternative for a slab foundation, in case of slightly less firm ground. The concrete strip either goes around the perimeter of the containers or just at the top and bottom of the containers instead. The strip is normally 1-2 feet wide and 4 feet deep and is often poured on top of a gravel strip that allows the water to drain away.

Pros

  • Less expensive than a slab foundation
  • Needs a moderate amount of trenching
  • Based on circumstances, the strips can be restricted to only two sides of the container

Cons:

  • Not Earthquake resistant

Pile Foundation:

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This type of foundation is used when the soil type is very weak and unstable or marshy. The cylindrical solid steel tubes (piles) are drilled deep into the site till it reaches the stable ground, and then they are covered by pouring concrete at the top. Its appearance is similar to that of pier foundation.

Pros:

  • Really effective for loose soil and marshy lands

Cons:

  • Most expensive type of foundation
  • The length of the steel rods required cannot be determined in advance
  • Needs professional help and equipment for design and construction.

Stone Foundations:

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Ever since concrete has become the conventional building material, we often tend to ignore the natural materials present in close proximity to the site. Stone foundations are one of the oldest and time-tested foundation types and are strong enough to stand for centuries if built correctly. Granite and quartzite stones are the most suitable type of stones for foundations of building in places with high groundwater levels.

So, if your region is abundant in these types of stones, these can be an inexpensive and sustainable material to build a strong foundation for your shipping container home.

Pros:

  • Inexpensive
  • Environment friendly and sustainable
  • Water-resistant- High water levels do not compromise with the strength or integrity of the foundation
  • Long life
  • Easy to deconstruct- If you decide to shift your shipping container home, this type of foundation will blend into the site naturally and will not leave any debris behind.
  • Aesthetically unique and pleasant. The aesthetics of the stone foundation looks marvellous with the raw Corten steel industrial look

Cons:

  • Need skilled masons to lay
  • Transporting the stone to the site could be an issue
  • Needs a considerable amount of trenching.

Temporary solution for a foundation for a shipping container home:

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Gravel pad for a temporary foundation

If you plan on using a container home as a temporary abode for a few months and do not wish to invest in an expensive foundation, you can use a simple, three-inch deep gravel pad that will level out the irregularities of the ground and prevent the container from getting crooked or sunken for a short period. 

Remember, ‘Temporary is the keyword here.

Bullet points on shipping container foundations

  • Even though Shipping container homes are popular as a DIY living solution, it is important to get the soil tested to determine the type of foundation needed.
  • If your site has marshy or very loose soil, it is advisable to hire a professional to help you design and lay the foundations depending on the number of containers in your home.
  • Make sure to give enough time for curing to the concrete foundations.
  • Stone foundations are also a time-tested option; however, it requires a technique. Make sure to hire the right people to lay it, or it won’t work effectively and can be fatal in the long run

Final Words

Foundations are a very important consideration while building any home. Even though they are below the ground, they define the strength and stability of the house. For shipping containers, of course, in some conditions, skipping or eliminating the foundation seems like a favorable option. But, if you plan to build a permanent shipping container home, then it is important to investigate the soil type and invest in the right type of foundation.

References

  1. https://www.discovercontainers.com/shipping-container-home-foundation-types/
  2. https://www.falconstructures.com/blog/shipping-container-foundations
  3. https://ripplesblog.org/tiny-house-gravel-pad-construction/
  4. https://icontainerhome.com/what-is-best-type-of-foundation-for-container-homes/