Slab-on-grade foundations refer to concrete floor slabs poured at ground level or grade to create a home foundation. Before starting the construction process, the contract excavates the soil (next to where to construct the foundation) and confirms the ground can support the structure.

Usually, the slab periphery is denser than the remaining surface. This section resembles the footer that enhances a  uniform circulation of the exterior walls’ weight over the soil below the structure. The slab-on-grade foundations work well in areas where soil cannot support basement foundations or crawl space foundations.

Also, you can use slab-on-grade foundations in areas with unsolidified grounds. Also, note that these foundations can or may not feature reinforcement in them. However, the reinforcement inclusion depends on the local construction codes and floor loads.

The grade slab should have a thickness of at least four inches. Increase the slab thickness if the soil features porosity. Besides this, to maintain construction safety, a bitumen layer and gravel layer should be positioned on earth before arranging the concrete slab. Through this, you’ll stop moisture content penetration into the grade slab.

Categories of Slab-On-Grade

Supported Slab-On-Grade


Supported slab-on-grade works great when the site already features conventional footings to hold up the columns. Under the supported slab-on-grade, the wall needs to be placed on a conventional footing and grade slab stand on the moisture barrier and gravel layer.

The formwork used on plinth beams works as the slab mold’s batter boards. Also, you have an expansion joint between the wall and the concrete slab to minimize the stress inserted during the high-temperature seasons.

The control joints must be installed in a grid designed with chalk lines. This feature plays a vital role in managing occasional slab cracking.

Monolithic Slab-On-Grade

Monolithic Slab-On-Grade

A monolithic slab-on-grade doesn’t feature footings. In this case, the slab itself works as a building footing, and the grade slab supports construction walls and columns.

Another thing to note about the monolithic slab-on-grade is that batter boards surround its structure. However, this structure relies on the design, and the concrete is drained inside the batter boards. Note that these batter boards work as a mold to identify the slab corners.

Note that grade slabs usually stand on the moisture barrier and gravel layers – which can resist water penetration into the grade slabs to create surface cracks.

Also, the grade slab features a very dense periphery than the remaining surface. This section plays a critical role by working as a mini building footing.

Applications Of Slab-On-Grade Foundations

  • Slab-on-grade foundations are highly popular in areas with warmer climates. Areas with warmer climates don’t find the thawing effect and freezing effect to be a challenge. As a result, this invalidates the need for installing heat ducts below the floors.
  • These foundations are very popular in areas with clay soil.
  • Slab-on-grade foundations work well on tract homes or constructions built with a limited/low budget.
  • These foundations work well on garages, barns, and sheds to deliver a beautiful floor without digging deep into your pocket.

Final Thoughts

Generally, if you decide to go with a slab-on-grade foundation, electrical and plumbing works must be positioned inside the building or below grade. This foundation requires the position of all wiring to be within a water-tight conduit. Also, all wiring must respond to replacement whenever there is a need for repairs or upgrades.

A slab-on-grade foundation requires you to dig deep into your pocket, and it makes construction go more quickly. However, this foundation’s pros outweigh the cons. For houses, it’s vital to have different foundations poured instead of dealing with issues associated with slab-on-grade foundations.

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