What is a thickened edge slab? Home Construction Concrete Tips

What is a thickened edge slab?

A thickened edge slab refers to a concrete slab or patio with a thickened edge. 

This means that the edge or perimeter around the concrete slab base thickness has been increased in thickness comparison to the rest of the concrete slab. Often the thickness could be up to double the thickness found for the remainder of the concrete slab. The thickened edge is usually sloped on the underneath to meet with the regular thickness of the concrete slab.

For instance, where a concrete slab is typically 4” (100 mm) or 6” (150mm) the thickness around the outside/perimeter of the concrete slab could be up to double the thickness. Generally though, about 2x or even 3x the thickness seen in the base slab thickness is typical. 

Reasons for a Thickened Edge Slab

One of the common reasons for a thickened edge slab is to increase the structural capability of the slab at the perimeter. 

There are a number of reasons that the concrete slab might have a thickened edge, and these reasons are dependent on the intent of the concrete slab in the first place. 

For instance, a thickened edge at a slab may be required to help support walls which are intended to be placed on the perimeter of the slab. 

Some typical reasons for a thickened edge slab include the following:

• To support additional loads from construction elements like walls, columns, beams, and openings for doors or vehicle traffic.
• A thickened edge slab can help reduce the effects of sub-surface settlement, which can stress a concrete slab.
• To reduce the formation of cracks.
• To combat the effects of frost-heave in cold climates.
• To make up for elevation differences from the grade to the top of the concrete slab.
• Can be used sometimes in lieu of a footing as an easier more constructable way to develop a strong base.
• To help support the edge of sidewalks or vehicle parking slabs where vehicle access points will be.

How a Thickened Edge Slab is Poured

A thickened edge slab will require that the base, sub-base, and sub-grade be adjusted to allow for the additional concrete to be poured. 

The additional thickness from the thickened edge has to be made up somewhere, and this is done by additional excavation at the area where the thickened edge slab is to be poured. 

As such, the placement of crushed gravel or other sub-surface building components should follow the line of the thickened edge slab. 

This way, not only can there be benefits from the thickened edge of the concrete, but the thickened edge benefits from the sub-surface gravel and/or crushed gravel as a solid base/sub-base on top of sub-grade.

Frequently Asked Questions – Thickened Edge Slabs

How thick is the edge typically?

The edge thickness of a thickened concrete slab varies but is typical around a foot or 2 feet in depth. 

Typically this would be for a slab thickness of around 6”. Again the thickness would coincide with the width of the concrete slab thickening too, often seeing 12” or 24” wide at the base of a thickened edge slab.

Does a thickened edge slab need rebar?

Yes, most likely. Typically a thickened edge slab has rebar because it needs to resist cracking and movements. The rebar also allows the thickened edge slab to carry more structural loads and tie the slab and the thickened edge/footing together.

Where is a thickened edge slab most common?

You will find a thickened edge slab common in residential garages, parking pads, carports, and general multi-residential parking areas. Small commercial buildings also often have thickened edge slabs and footings. Structures with slab-on-grade(SOG) construction also are typical to have thickened edge slabs.

How to pick the right concrete contractor?

If you are unsure if you need a thickened edge for your concrete slab then refer to the specialized services of a professional concrete contractor. Don’t know one? Not to worry! The professionals at Deluxe Concrete Services provide professional Calgary concrete services and know just how to utilize thickened edge slabs for their exact intended purposes.

Any solid professional concrete contractor will be able to utilize this construction method to their advantage. You as a homeowner can also gain some valuable insight from this post, in seeing where and why a concrete thickened edge might be used for your home or new structure.

What are some issues with thickened edge slabs?

Generally there could be issues with cracking if the footing and thickened edge is not reinforced properly.

Also settlement if the subgrade preparation is poor is another concern. Make sure that insulation is used where applicable in cold climates.

Summary

A thickened edge concrete slab is typical in parking lots, driveway Calgary concrete, and light commercial buildings. The thickened edge of the concrete helps to prevent cracking and resist edge breakage. 

It can also have benefits for resistance to frost heave, erosion, and any potential undermining of the sub-base and base from water. This sort of approach to concrete slab construction can also allow a footing to be poured with the slab, where the thickened edge of the concrete slab acts to support the slab like a footing.

You will find thickened edge concrete slabs common in residential, light commercial, and even landscape construction techniques.