The best building projects begin with a good foundation - literally. If the foundation isn’t right, there will be a negative impact on the durability and longevity of your metal building, two of the most common benefits you receive from building with steel.
Let’s take a look at some common questions about foundations for metal buildings.
Is the foundation the same as the floor?
In a metal building, the foundation is often used as the floor. Particularly in structures that see heavy traffic, support heavy equipment or require easily cleaned floors, a concrete floor is preferable.
The foundation engineer needs to know how much and what type of weight the floor will support. Reinforcing the foundation with steel rebar can mitigate cracking. Laying a sheet of polyethylene on the surface before pouring the concrete prevents water vapor from seeping up through the concrete floor.
Is the foundation part of the building system?
No. To obtain a set of stamped engineered foundation plans for your steel building, the foundation engineer must have a set of building engineering plans already. Without the building plans, the engineer will not be able to design a foundation. It can’t be done the other way around.
Also, the foundation engineer is typically hired by the contractor on a per-project basis, not by the metal building manufacturer.
Why is the foundation designed before the building is available?
Steel buildings are designed from the bottom up, the opposite of wood-frame single-story buildings. Therefore, the frame analysis is not complete nor are the column reactions known before the foundation is designed.
The foundation and building are designed separately, by different companies, and the metal building manufacturer may not offer foundation engineering services.
Also, the concrete must be allowed to cure before the building is erected. Taking delivery of the building system before the foundation is ready raises the potential for theft or vandalism of the site.
Are there different types of foundations?
Yes. Yes, there are.
- Slab foundations (floating slabs) are the most popular choice for steel building foundations. Slabs are the type used when the foundation is also the floor.
- Pier foundations are used for structures that require a dirt or gravel floor. Concrete piers and footings are buried beneath the soil to support the building frame. Agricultural buildings and buildings that will not often be enclosed use pier foundations. Fewer problems with shifting soil are found with pier foundations.
- Perimeter walls are also called perimeter footings and are poured around the exterior of the structure to support the outside framing walls. Perimeter walls can be used in combination with slab or pier foundations.
Consult with the foundation engineer to determine the best type of foundation for your steel building.
What’s the difference between steel building foundation and foundations for other types of buildings?
A steel building will have more movement than concrete or masonry buildings. There will be a larger columnar uplift, and the foundation may be designed before the column reactions are known, or the building system delivered. Steel building foundations are generally less expensive since the walls are non-load bearing. In other words, the foundation does not have to hold up the walls of the steel building like concrete or masonry buildings.
Foundation design is inspected a second time after the building design is complete to ensure it is adequate.
Does soil type make a difference in steel building foundations from foundations for other types of buildings?
Before construction begins, the land is surveyed for site levelness and to mark the boundaries of the plot. Once the survey is complete, the plot is often graded. At that point, you can learn what type of soil your foundation will sit upon.
Poor soil conditions may require a thicker foundation or more reinforcement to protect it against upheaval and cracking. Bringing in a better grade of dirt to spread on the existing earth may be a less expensive alternative to a thicker foundation, depending on price and availability of materials and fill dirt.
Ask your concrete contractor or engineer for advice on your specific site.
How is a foundation poured?
- Forms of wood or metal are placed around the perimeter of the foundation to hold the concrete together as it cures and to create the correct shape. Forms should not deform, bend or deflect due to the weight of the concrete.
- The concrete is kept mixed, so the aggregate does not sink to the bottom. It is poured evenly across the entire foundation area. Reinforcing bars are completely covered, and no voids or air bubbles are allowed to be trapped within the pour.
- Any water forced to the surface by the pressure of the sand and aggregate (called latinate) is removed as soon as it appears.
- The foundation surface undergoes screeding, a method of leveling the floor by pushing excess concrete away and pushing concrete into lower or under-filled areas.
- The surface is finished using wood or metal floats to compact the concrete and push larger aggregates back into the mixture. The surface is then smoothed with hand trowels or ride-on trowels.
What is meant by “curing” the concrete?
Concrete must cure before you can erect the building frame. Curing is the hardening that occurs due to the chemical reaction between the concrete admixture and the water used to hydrate it for pouring.
Maximum drying strength is reached after 72 hours as long as the temperature is between 50 and 90 degrees Fahrenheit for the entire time. If temperatures fall below 50 degrees, take extra care to ensure the concrete can set properly; otherwise, you can lose 50% of the cohesiveness and strength of your foundation.
Can I use an existing foundation?
Using an existing slab foundation is not recommended unless you can guarantee it was designed and poured exactly right for your new steel building.
Most people do not know the preparation work, the quality of the concrete or the conditions of the pour for an existing foundation. Trying to save money by using it can cost much more down the road if your steel building is damaged or collapses because the foundation was not properly engineered.
Even if you attempt to use the existing slab, it’s likely that it will require modification, which requires the services of a foundation engineer to determine the type of modifications required and whether they are feasible.
If you have any other questions about foundations or steel buildings, contact Whirlwind Steel. We would be happy to answer any questions you may have.