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Breaking Down Concrete Slabs & The 3 Main Types

  

“A strong foundation is the key to creating long-term success.”

— Michael Leonard

Buildings are only as strong as their bases, right? When it comes to commercial real estate development, choosing the right type of concrete will determine whether your building’s future will maintain a strong foundation.

 

Information to Know:

First, let’s break down the basics of what you should know about concrete slabs. A standard slab for single-floor buildings and pavements is 4-5 inches, but will increase in thickness based on site conditions or tenant’s use. 

For instance, a warehouse slab will likely be thicker to handle the load and forklift traffic. Foundation walls for one-story buildings should have a minimum thickness of eight inches. General contractors understand that concrete does shrink during its curing period (about 28 days) and should account for it.

Example: Slab Design Criteria: Min. slab thickness shall be five inches, based on a minimum 3,000 PSF soil bearing pressure, 100 PSF uniform floor design load with 400 psf fixture point loading.

 

To help counteract the immense pressure a commercial building brings, a strong anchor system should be put in place to distribute the weight more evenly and reinforced. You should also conduct a special inspection to verify the concrete strength by doing a break test. This type of test measures the compressive strength by breaking cylinder-shaped concrete samples in a compression-testing machine.

Calculated by: Failure load divided by the cross-sectional area resisting the load and reported in units of pound-force per square inch or megapascals. Then, the average of three tests of concrete, aged at least 28 days, is recorded as the result. Here is more information on break tests.   

 

Important to Note

No matter how perfect the concrete is that you choose, if the earth is not precisely leveled, it will negatively affect the floor thickness throughout the slab. Concrete is relatively inexpensive, but you need to choose the right type for your climate and building type/strength requirements. 

For the specifications submittals, you will need to stay current on requirements and concrete design knowledge. You can reference up-to-date specifications, codes and standards here: American Concrete Institute (ACI), American Society of Testing and Materials (ASTM), and International Building Code.   

 

3 Types:

  • T-shaped Concrete Foundation (Footing Design Foundation)

This type is the most common in commercial buildings and is considered the traditional foundation method. It especially helps support taller buildings and is ideal for colder climates where ground freezing may occur. A high amount of pressure is exerted on the foundation when the ground freezes, and this foundation requires placing footing below the frost line. The walls are then added on the footing, which is wider than the wall so it provides more support. 

 

  • Slab on Grade Concrete Foundation

On the opposition, slab-on-grade foundation is used where there is no threat of ground freezing. This method involves a single concrete layer that is several inches thick and poured all at one time. It is poured thicker on the edges of the base to create an integral footing. Furthermore, reinforcing rods are installed at each edge for even more support. Note: This type usually sits on crushed gravel, which improves the foundation drainage. However, to minimize risk of cracking, wire mesh is placed over the slab

 

  • Frost-Protected Concrete Foundation  

If the area is in fact susceptible to the ground freezing, this type of concrete is an even better option to the slab-on-grade because it uses two sheets of rigid polystyrene insulation. The insulation sheets hold heat from the structure. This method only requires one concrete pouring, while the T-shaped foundation typically needs three. 


Builders are skilled in considering the type and durability against the overall cost in order to elicit a long-lasting foundation for your property. Consider partnering with a preferred developer who is highly skilled in this department.

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