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Evaluating foundation options for prefabricated steel buildings

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Evaluating foundation options for prefabricated steel buildings

Pre-engineered metal buildings make efficient use of structural steel using building information modeling (BIM). This can cut building costs by as much as 20%, but it also makes steel buildings very light. Because of this, steel buildings are susceptible to wind uplift forces — steel building foundations have to be large to counteract wind uplift and ensure the long-term safety and durability of your building.

While prefabricated steel buildings tend to beat other building types in terms of overall cost and value —even when you factor in foundation costs— their foundations are often more expensive than other building types.

Because the foundation makes up such a large proportion of the total cost of your metal building, it is important to work with your general contractor, erector and metal building manufacturer to weigh your steel foundation options carefully.

Three common steel building foundation options and when to use them

Your concrete engineer will evaluate site-specific soil conditions, local building codes and climate conditions to determine the most cost-effective foundation type to meet the design parameters required by your building.

Here are a couple common foundation options they might consider:

Floating / monolithic foundations

Floating foundations continue to be the most popular of the foundation options due to their affordability and ease of construction. If the soil will support a floating foundation, it is installed as a concrete slab with one continuous grade that has reinforcement under each of the columns. These foundations do not require as much digging or time as other foundations and can be completed much more quickly. And after construction, the concrete of the slab will become the floor of your building.

Although floating foundations are the best option for most applications due to the low price and speed of constructions, they do not offer the level of stability needed in regions with higher prevailing winds or poorer soil conditions.

Pier, footing and grade beam foundations

Poorer soil or problematic bearing pressure conditions may make pier, footing and grade beam foundations a necessity. In this case, concrete piers are set deep into the ground (past the frost line) to bear the weight of the building. Though it is often a more expensive option than a floating foundation, the depth of the piers can often better resist wind uplift and can be linked to resist shifting. They are often used in agricultural buildings for livestock or for open-air structures like pavilions.

The biggest drawback of pier, footing and grade beam foundations is their higher cost. But in some applications —such as an open riding arena susceptible to wind damage— the added stability they offer may warrant the cost increase.

Perimeter walls

Often used in conjunction with slabs or pier foundations, perimeter walls support floors and load-bearing walls. Perimeter walls, also known as perimeter footing, are poured around the outside of the structure, reinforcing the exterior framing walls. Perimeter walls will typically be equipped with rebar to resist hydrostatic pressure from the outside of the wall.

And while they add load support to your foundation, load-bearing perimeter walls are not recommended in regions with high flood risk, according to the Federal Emergency Management Agency. That is because the soil around vertical foundation elements are especially susceptible to erosion by flowing floodwater — which could compromise the structural integrity of your foundation.

steel building’s foundation ensures its safety and durability over time. And although foundations for prefabricated steel buildings can be more expensive than those for conventional buildings, these costs are typically recouped in the lower material and construction costs of a steel building. You will want to work closely with your general contractor and concrete engineer to consider factors like location, soil, load and wind uplift to plan the most cost-effective foundation for your application.

Who is responsible for designing your steel building’s foundation?

When you purchase a pre-engineered steel building package, it will come with all the metal building components required to erect your building, the standard building features provided by your manufacturer and any optional features you added to customize your building. It will also include stamped and certified metal building plans (detailed diagrams of your building design) and anchor bolt plans (showing the diameter and projection of all anchor plants, as well as the reactions of the steel on the foundation).

Your metal building will not, however, come with a foundation plan. Since your foundation design will depend on site-specific (e.g., grade, soil type) and location-specific (e.g., climate, prevailing winds) conditions, it is best to have a local concrete engineer design your foundation. They will be the most familiar with local codes in your area, as well as foundation design best practices in your region.

Your general contractor will typically coordinate with a concrete engineer to design and construct your foundation. If you are serving as your own GC, you will need to coordinate the construction of your foundation before the arrival of your building to allow for immediate erection.

Here are a couple factors you, your concrete engineer and your GC will need to consider when planning your foundation:

Evaluating soil conditions and bearing pressure

You will want to test the soil on your site to allow for accurate analysis of the risks associated with building on it. If soil type and bearing pressure are not accounted for in your foundation design, it can leave your building vulnerable to settling, shifting or structural damage.

Highly expansive soils, such as those under most of South Dakota, can expand like ice when wet and threaten the integrity of the building and its foundation. Soil’s bearing pressure, which affects how much force it will support, should be within a particular range to be cleared to build. There are ways to counteract these risks (i.e., ground improvement when the load of your building is greater than the bearing pressure of the soil), and it is important to understand the design parameters of your site prior to designing your foundation.

Counteracting horizontal loads

Steel buildings typically are characterized by high horizontal loads and can be susceptible to damage by high winds, heavy snow loads or earthquakes. You will want to discuss these factors with your local contractor to ensure your project considers these situations.

In areas with high prevailing winds such as Florida, for example, it might be wise to increase the footing size to prevent wind damage. Large, open metal buildings —such as riding arenas, pavilions and some agricultural buildings— are especially susceptible to wind uplift and may also require heavier foundation designs.

To learn more factors you need to consider when purchasing a metal building, check out our guide to capturing value with metal building. You will learn simple ideas to save you thousands in operating costs over the life of your building.