Well-designed and constructed foundations are important for steel buildings. However, foundations are often given less attention than the accompanying above-ground metal structures. Many potential buyers are confused about how to plan and build a foundation.
A proper foundation is critical to the success of a building project. Weak foundations can cause walls to tilt, and floors to sink, and are susceptible to damage from earthquakes and strong winds. These problems can lead to safety hazards, costly repairs, or render a building unusable. Sometimes it may be cheaper to tear down a building and start over than to repair a problematic foundation.
Foundations for prefab metal buildings are different and often more complex than those for regular buildings. It is important to note that metal building kits do not include foundations or anchors. Therefore, you will need to find a local engineer to plan the foundation and a trustworthy contractor to build it.
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Important information about building metal building foundations
Here are some important points for designing and constructing foundations for metal building systems:
All metal buildings require a concrete foundation, usually a leveled concrete slab. However, some farm buildings and sheds may not require a concrete floor. The type of foundation and floor slab for steel buildings depends on the purpose, size, and location of the building.
The soil needs to be inspected before proceeding with the building project to ensure that it will support the foundation. If necessary, better quality fill should be used.
Make sure you follow all building rules and laws. Local building codes will tell you how deep the foundation needs to be (to protect against freezing) and the minimum thickness and strength of concrete. Local rules and codes may specify the maximum size of a building that can be constructed without a permit. For example, the 2021 International Building Code (IBC) indicates the types of buildings that require a permit. Examples include small buildings with tools and storage and utility buildings with more than 120 square feet of floor area.
Typically, a licensed structural engineer should create the foundation. Unless you are building a small metal shed under 120 square feet, it is not a good idea to plan and build the foundation yourself. If anything goes wrong with the foundation, it can be difficult and costly to fix. So you shouldn’t try to save money in this area.
Structural engineers understand the best ways to create foundations for metal buildings. However, not every engineer understands the unique issues involved in designing these foundations. Steel building foundations are different from regular building foundations. Ask your engineer to follow the Guide to Designing Foundations and Anchors for Metal Building Systems by Alexander Newman.
Metal Building Foundation Design
1 Factors Affecting Foundation Design
1.1 Soil Composition
You need a strong foundation for your steel building. So, you’ll need to look over the soil at your location. The nature of the soil is important for the safety and durability of the prefabricated metal building. In addition, could you please know the frost line in your area? This is because the foundation of your building must be below the frost line.
1.2 Building Loads
In addition, you need to consider what structural loads affect steel buildings. Professional structural engineers understand how to calculate structural steel loads. So, I’d like you to please try to hire a professional.
- Wind Loads. Prefab metal buildings are much lighter than other types of buildings. Therefore, they need strong foundations. Otherwise, a strong wind may weaken the building. Imagine a metal house like a large sail supported by a few sturdy pillars. Steel building foundations usually need to be stronger than those of other buildings. This is because they must hold the structure in place against strong winds and lateral forces.
- Snow Loads. The amount of snow on a building can also affect the size of the foundation due to the weight of the snow pressure. This is the common snow load for steel buildings.
- Seismic Loads. In areas of high seismic risk, building codes require specific foundation designs.
1.3 Building Size
Large metal buildings may require a different type of foundation than smaller buildings. This is because they carry more weight on the ground. Foundation engineers need to know the dimensions of the building you are purchasing and the location of the footing bolts that connect the steel columns.
1.4 Possibility of Future Expansion or Weight Addition
If you plan to expand or increase the weight of your steel building in the future. Then it is a good idea to design the foundation to support these changes. This is because it will be more difficult and costly to expand the foundation at a later date.
2 Who is Responsible for Designing the Foundation?
Foundations for steel buildings should be designed by a professional structural engineer with extensive experience. This is because building strong foundations requires special knowledge and skills.
3 Do I Need a Foundation Plan for a Metal Building?
Yes, you need a foundation plan designed by a licensed structural engineer. Metal building kits include detailed plans, but not foundation plans. Therefore, a foundation plan approved by a professional expert is usually required when applying for a building permit.
In addition, your concrete contractor will need detailed foundation plans and details. This will allow them to provide an accurate price for the foundation required for your building.
4 Foundation Design Process
Building contractors typically list the building’s response to a variety of loads, including live loads, dead loads, snow, wind, and any other necessary loads. The structural foundation engineer uses these responses to select the most appropriate type of foundation. This ensures that the steel foundation will safely resist the loads it is subjected to.
There are two main differences between foundations for regular buildings and foundations for metal buildings:
- As mentioned earlier, a strong foundation is needed to resist wind uplift.
- Most metal buildings use rigid frame structures for support. These frames exert vertical forces on the foundation. In addition, it simultaneously generates horizontal forces that push the foundation to the side. And this is not common in traditional post-and-beam construction buildings.
As a result, the foundation of a steel building is likely to be stronger and different from the foundation of a large house or a two-story office. This is because heavy upward and sideways forces are not present in the latter’s foundations or are balanced by the weight of the building.
Selection of Foundations for Metal Buildings
There are many types of foundations for steel buildings. Some foundations cost more but are more effective. Some foundations are inexpensive but not trustworthy. Therefore, care must be taken when selecting foundations for steel structures. Foundations that are suitable for small buildings may not be suitable for large metal commercial buildings.
The most common types of foundations used for steel buildings are the following:
1 Tension Rods and Column Footings
Connecting the foundations on opposite sides of a rigid frame reduces the horizontal forces on the columns at each end. Tie rods vary in price and reliability. Some tie rods are inexpensive but less reliable, like adding a few bars to a thick concrete slab. Others are more expensive but more reliable, such as concrete horizontal beams. The column base of a steel building must be strong enough to withstand wind pressure.
2 Hairpin Bends + Column Footings
They work similarly to tie rods but utilize a footing to withstand lateral forces. Hairpins were commonly used in the past, but today’s rules make them less cost-effective. Since the floor slab is now part of the structure, it needs to be built as a raised structural floor.
This means it should be reinforced with rebar rather than wire mesh and should not have any control joints. If the floor slab is later cut for the purpose of installing utilities, the system will no longer work. Therefore, use this method with caution.
3 Bending-resistant Foundations
This is the most applicable method for steel building foundations. It is also commonly used for non-building structures. Bend-resistant foundations work similarly to cantilevered retaining walls with a wide base. This helps prevent the foundation from tipping or rolling.
4 Slab Foundation with Soffit
This system is known as an under-turned slab and is commonly used in the construction of houses. It functions similarly to an anti-bend foundation, and if properly designed, the supports will be similar in size to the base of the foundation. Instead of the small, narrow soffit that builders usually expect. This design should be avoided except for very small metal houses. In addition, such systems do not work well in cold locations.
5 Concrete Pad Support
These pads are thick and are reinforced from both the top and bottom. They may be heavy enough to withstand strong winds. In addition, their reinforcements can act as distributed ties. It should be noted that they are relatively expensive.
6 Concrete Piles
Concrete piles are expensive and are usually used in poor soils. This is because shallow foundations are not a good option in such soils.
7 Deep Pier Foundations
These deep pier foundations are used as pile foundations in soft soil areas. They are quite economical and are commonly used for steel building supports and non-building structures such as highway signs and utility poles. In addition, these foundations are not dependent on the slab on grade, making them suitable for farm buildings. Deep piers can be used with sturdy exterior beams.
Whichever method you choose, foundations must be strong enough. This is because they need to withstand wind-lifting forces, not just support weight from above.
Start your project today with a tailored price estimate for your steel building.
Small Metal Building Foundations
These buildings include metal garages and residential storage units. These steel buildings’ dimensions do not exceed 30×40. As mentioned earlier, if these buildings are at least 120 square feet in size, they usually require a building permit. They will also likely require a set of foundation drawings by a licensed structural engineer. In addition, the best foundation system for these metal buildings is:
- Tie rods + column footings
- Hairpins + column footings (use with caution)
- Slab with haunch (use with caution)
- Mats
- Drilled shafts
It should be noted that most of these building projects require the use of ground-floor foundations.
Agricultural Metal Building Foundations
This type of building includes storage barns, riding arenas, and similar structures. They typically have dirt floors and range in size from small 40×60 steel buildings to much larger buildings covering thousands of square feet. As mentioned earlier, these homes will likely require a building permit. In addition, they will likely require a set of foundation drawings by a licensed structural engineer.
Since these buildings usually have no floor slabs, the best foundation method is:
- Moment-resisting foundations
- Drilled shafts
Foundations for Large Commercial Metal Buildings
This category includes medium to large warehouses, community buildings, and commercial buildings. Due to the high loads carried by the foundations. Therefore, these buildings require the most reliable solutions. You may need a set of foundation drawings prepared by a professional structural engineer. The best foundation method suitable for commercial metal buildings is:
- Tie rods + column footings
- Moment-resisting foundations
- Mats
- Piles
- Drilled shafts
Most buildings will require a level base (floor slab) and will have walls or beams at the edges that are below the frost line. In addition, the building’s columns will be supported on pilasters. A structural engineer will develop plans for all of these things.
Anchor Bolts for Metal Buildings
Anchor bolts are also very important when installing steel buildings. They can support the building columns during the installation of the steel structure. In addition, it helps in transferring wind and seismic forces from the framed structure to the foundation.
The type, size, length, and number of anchor bolts depend on your building. These anchor bolts are very important and must be designed by a licensed structural engineer.
1 Accuracy of Placing Anchor Bolts
Prefabricated steel buildings must be installed very accurately. If the anchor nuts are not placed correctly (even by an inch), the columns cannot be installed on the foundation. Therefore, assembly should be done by skilled professionals, such as surveyors and field engineers. General labourers should not do this work.
2 Placing the Anchor Bolts
The building supplier will provide you with specific plans, such as drawings and numerical specifications, for the type and location of the bolts. You will need to provide this information to the foundation designer and contractor. This will make it easier for them to know where the bolts will be located before the concrete foundation is poured.
Summarizing
All types of steel buildings require a proper concrete foundation to hold the building in place. The exact type of foundation depends on the loads on the building columns and the soil on site. In addition, most metal buildings require strong concrete floors. And some buildings, such as agricultural storage buildings, require only dirt floors.
