Deciding to live in a shipping container unit is a bold decision to downsize many things in your life. Less space in your home, a lower monthly payment on it (if any), smaller kitchen, smaller bedrooms, etc... But many people overlook the most important thing: the need for a shipping container foundation!
While not all of our customer use a concrete foundation (some just place it on the ground directly), you will see in this post why we recommend placing your home on some sort of foundation!
This is one of the most critical steps in building your container home, because if you do not have a solid and sturdy foundation it can damage your new home and end up costing a lot more to repair it or rebuild the foundation correctly after the home has been placed on it.
Unlike a traditional home, which is typically built on a concrete slab, there are four types of foundations to choose from when prepping your Shipping Container Foundation.
They are: Slab, Pier, Strip, and Pile Driven. Each has different applications and situations where one is more appropriate over another one.
Factors include budget, structural requirements depending on the type of home, size, etc., local soil type, and local building codes and requirements.
In this article we will discuss the different types of foundations, which one you should consider and why, and what to look for in your specific location where you are thinking of putting your new home.
Do I Really Need A Foundation For My Container Home?
Soil is unpredictable. Rain, ground water, wind, erosion, earthquakes, these can all contribute to soil becoming unstable and then the risk of the Container home moving, sinking, rising, or sliding can occur.
Most of the time we take soil for granted and see it as stable, however it can shift under the right conditions which would then cause a lot of potential problems for your home. The soil could become unleveled which could damage and safety issues.
A foundation will provide for a solid and stable platform for your new home and will help decrease the risk of structural damage happening to your investment. This will also increase the lifespan of your Container home.
The soil that we typically see is called top soil, which may or may not be made up of all the same material. As you dig beneath the top soil you can come across a variety of different materials such as hard rock or soft clay, or even a combination.
With weight distributed across the ground, settling will occur and the elements that we listed above can work its way into the deeper levels of soil and over time cause the home to shift due to the uneven material. This can result in quite a few problems, such as doors and windows becoming out of square, which means they will not open or close correctly.
A well-built and sturdy foundation will secure the home and will distribute the weight of the home evenly. It also ensures that if erosion does occur your home will be well secured and safe.
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How Do I Know What Type Of Foundation I Need?
There are two major factors that will determine which foundation type will be best for your location and container home. Those factors are cost and what is required structurally.
The best and correct way to calculate which method to go with will require meeting and consulting with a local qualified builder or local engineer. Soil type and how many containers you are planning on placing on your land will play a large factor here.
If you are building on a softer soil you will then need a deep foundation, such as pile foundations.
If you are building on a harder soil you can then go with a minimal foundation type. The reason for this is because the majority of the weight of the container will be evenly distributed onto the existing hard top soil.
Depending on some peoples budget they will do what is called ‘over-spec’ on their foundation, which means building a stronger foundation than what is required. There are a couple of reasons for that, from peace of mind or because they prefer a particular foundation that is more than what is required.
That decision will ultimately come down to cost, design, and what the local building codes require structurally.
What Are Your Shipping Container Foundation Options?
Any foundation that is used in building a traditional home can be used in the same applications for Container home foundations. The foundations can be classified as either shallow or deep foundations.
A shallow foundation is laid close to the ground level, as much as a foot or two down from the top. Deep foundations can be laid at depths of up to 32 feet (10 meters).
Piers are an example of a shallow foundation and are one of the easiest, and cheapest, concrete foundations to do.
To sum up what they are made of, they are concrete cubes which are reinforced with rebar (steel) within them, or a mesh of steel wires. The steel adds a lot of strength to the concrete for a very sturdy foundation.
Shipping container homes set on concrete piers usually will have a pier at each corner of the home. And if using 40-foot container an additional two piers are needed and are placed halfway down the length of each side of the home.
The best reason for going with a pier foundation is that because the container will be lifted off of the ground it allows for greater ventilation and will help prevent condensation from forming underneath the container home.
Pier foundations are chosen quite often by DIY home builders as they are the simplest, cheapest, and quickest foundation to lay down. It doesn’t require any special equipment, and it doesn’t require very much experience to DIY.
It will save a lot of time and money by choosing pier foundations as you don’t need to excavate a ton of dirt to achieve the required depth. You would only need to excavate the ground for the piers. Generally, all that is required is a 24”x24”x24” holes.
Compare this to a concrete slab where you will need to dig for footings, you would need to excavate more than 20 (or 40) feet by 10 feet, or more, and will need equipment to excavate the area.
A slab foundation is the most time-consuming foundations of the four. It is the preferred method when encountering soft ground and the need to equally distribute the weight of the home.
A slab foundation, or concrete slab, can be either built to the exact dimensions of the container, or if cladding is going to be added to the container then you would want to build it slightly larger than the footprint of the container so that the cladding can also rest on the slab.
Depending on the soil type, local water tables, and the frost level in your area the foundation may be dug as shallow as 18-inches all the way to 10-feet.
A couple of reasons to choose a slab foundation, in addition to soil type, is it provides a solid base with no pockets or dead space underneath the container home. This can help prevent a lot of problems, such as bugs, cold/hot pockets, and spreads the load of the container over a larger area than a pier foundation.
Due to the additional concrete that is used in a slab foundation, and with the amount of soil that needs to be excavated slab foundations are vastly more expensive over using pier foundations.
Something to note with going with a slab foundation is that once the concrete is set there is no way to access utility lines like there is with going with a pier foundation. If a water pipe leaks or breaks, then a section of concrete will have to be cut out to access the pipe.
A slab foundation is possible as a DIY but will require an excavator if you need to dig very deep, which can also be DIY. Most equipment rental places will have some kind of an excavator for rent.
However, it is always best to either consult with an architect engineer or have a contractor do it for you.
A strip foundation (also known as a trench foundation, or footing) is a combination of pier and slab foundations. Typically, when building a slab foundation, a strip, otherwise known as a footing, is laid down before the slab for stability and strength.
A strip foundation is a strip of concrete which is laid to support the container. Usually the concrete strip is 1-2 feet wide and can be anywhere from 2-4 feet deep.
A strip foundation can be built in a couple of different ways; as a perimeter of the container or it can be built at the top and bottom of the container.
This is a great option if on a budget and want to keep costs down instead of doing a slab foundation but have less firm ground to lay your foundation on.
In areas where the ground stays damp for much of the year because of heavy or constant rain, a rubble strip foundation using loose stones below the concrete strip can be used. This will work as a filtration system by allowing the water to run through the stones and drain away.
As with the other foundations that we’ve discussed strip foundations also have weaknesses. Strip foundations have a weak resistance to wind and earthquakes. Due to their shallow form strip foundations are best used for a small or medium-sized build.
Pile foundations are utilized when the type of soil in your local area is too weak to support a concrete base. It also happens to be the most expensive foundation that we’ve discussed in this article.
Piles are a cylindrical solid steel tubes that are hammered into the ground until the piles reach a more stable load bearing ground.
Pile foundations are not recommended as a DIY build as they require specialized equipment. A contractor would be needed to install the foundation due to the specialist equipment, typically a pile driver.
After the piles are driven in place and secured, they are usually capped with a block of concrete. Once all the piles are secured you end up with a grid system of concrete caps which look very similar to concrete piers.
What Type Of Concrete Should I Use For My Shipping Container Foundation?
There are a variety of different concretes, and a lot of different strengths of each type of concrete. The strength of concrete you will need to use for your foundation will be decided by a geological engineer’s report.
You can always go higher and above the recommend strength, but never under the recommended strength. You run the risk of failing your building permit if you go under what has been recommended for your foundation and will then have to redo the whole foundation, costing more money and time.
The scale we’ll use to describe the different types of concrete is the megapascal (MPa), which is a x100000 multiple of the pascal unit which is the SI unit for pressure.
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This concrete is made by mixing the basic ingredients of cement, water, and aggregate. The common ratio for this is 1:2:4. The strength of this type of concrete will vary from 10MPa to 40MPa. This type of concrete has an initial setting time of 30 to 90 minutes.
This time will vary depending on the cement properties and on the weather at the site. Sunny, hot days will see the concrete set up faster, while colder days gives you more time to work it.
Reinforced concrete is when a reinforcement element is added to bear the tensile strength. Normal concrete is weak in tension, but good in compression. As was mentioned earlier in this article, the most common reinforcement is steel. Fibers, such as fiberglass, can also be added as a reinforcement.
Ready Mix Concrete:
Ready mix concrete is concrete that is mixed at a central mixing plant. The mixed concrete is then sent out to the site of the construction by a truck-mounted transit mixer, the trucks that we’ve all seen driving around with the barrel mixer on it. This is ready to use immediately at the site.
Ready mix concrete is made to precise measurements and specifications. There are chemicals and ingredients that can be added to slow down or speed up the curing time, these are called retardants. An example would be adding calcium on a cold day to speed up the curing time of the concrete.
Typically, if you are using a ready-mix cement company it will be in relatively close proximity to your location.
If transportation is too long the result will be that the concrete well set on the way to the construction site and not only will be unusable but will also harden in the barrel of the truck. So, there is a time restraint with using ready-mix.
These three types of concrete are the most common, and the ones you would typically use in constructing a foundation. There are a lot of other, different varieties of concrete available, but again which one you choose would be based on the recommendation of the engineer.
What Steps Can I Take If I’m Pouring On A Hot Day?
If you are pouring concrete in the summer, or in hot weather, it is very important to have your site prepared correctly before the cement arrives. Before you begin pouring you should heavily spray the ground with cold water, and if you don’t have access to cold water it is still beneficial to spray water on the site of the pour.
If you are mixing the cement yourself, you will want to use cold water as hot water will cause the cement to set faster.
Another way to work the concrete on a hot day to ensure that you have time to work it, is to pour first thing in the morning or late in the evening to avoid the hottest time of the day.
What Steps Can I Take If I’m Pouring On A Cold Day?
Pouring concrete in cold weather requires special measures just as hot weather days. Cold weather is classified when the average daily temperature is below freezing for more than three consecutive days.
Before pouring the concrete, you need to make sure any snow or ice has been moved and cleared from the base and forms. Any standing water will also need to be removed.
Once you have poured the concrete and finished it, you need to cover the concrete with insulating blankets as soon as possible.
You will want to keep the blankets on the concrete for 3- 7 days while the concrete is curing.
Once the concrete has cured you will want to remove the blankets gradually so that the concrete doesn’t crack, or break, due to quick temperature change.
Now That I Have My Foundation...
How Do I Attach My Container Home To The Shipping Container Foundation?
The most common and popular method for attaching a container to the foundation is by using a steel plate. Once the concrete has set up and is still curing, a steel plate with vertical bars is set into the wet concrete and carefully moved down until it is level with the top of the concrete, or flush.
Once the concrete has cured, usually about a week after pouring it depending on weather conditions, the container can then be placed on the foundation and welded to the steel plate. This creates an extremely strong bond, and generally the preferred method of securing the container to the foundation.
If you don’t have access to a welder or prefer a different method then you can bolt the container to the concrete using concrete anchors, or bolts. This is a simpler and easier method, but the hold isn’t quite as strong as welding to the container. It will still create a strong bond between the container and foundation.
If you are not planning on having your container home permanently attached to the foundation, then you can simply place the container onto the foundation. You will be sacrificing some strength of the home if you plan on using this method, but you could use straps that go over the container to secure it to the foundation to give you a bit more strength against strong winds and storms.
The only time you would be able to use this method would be if the container is going to be portable. You’re local building codes will require that the unit is secured to the foundation.