What Is Grade On Slab?
The Slab On Grade is defined as a directly laid on the earth’s surface for supporting the structural elements and walls. The minimum thickness of grade on a slab depends upon the soil characteristics and porosity and generally 4 inches thickness is considered on the grade of the slab. The slab on grade is also known as a floating slab.
Slab on Grade is popularly used in that area where the ground doesn’t freeze. These types of slabs may or may not use reinforcement and the decision to insert or use reinforcement depends upon the local building codes and floor loads.
For safety purposes, a layer of bitumen and gravel is laid on the earth’s surface before laying the concrete slab to prevent moisture from the slab.
Also, this type of slab is directly prepared on the ground level or earth level, slab on grade acts as a foundation for any structure or building. Which does not require a further type of footing.
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Construction of Concrete Slab On Grade
Before the construction of grade on a slab, initially the earth up to the required depth and compacted the earth’s surface to remove air voids from the surface. Batters are placed in position as per plan before pouring the concrete in it and this board acts as a mold that helps to identify the corners of the slab.Â
Soil investigation is done then design to the thickness of the slab as per the investigation result and another layer of bitumen and gravel is poured into the earth’s surface.
This gravel and bitumen layer acts as a sub-base layer for the concrete slab. This is preventing the entry of groundwater into the slab. The pouring of concrete is thicker at the edges of the concrete slab, and that acts as a footing, and also reinforcement bars are provided at the edges for strengthening purposes.
To minimize the cracking problem control joint I the slab and also expansion joint are placed between the slab and wall, to cure the stress action in the high-temperature period.
Types of Grades on Slab
The following two types of grade on a slab are described below,                        Â
1. Supported Slab on Grade
Supported slab on grade is as the name suggests this slab supports the already having traditional footing on the field or site.
The supported grade on the slab also acts as a moisture barrier and an expansion joint is provided between the wall and concrete slab for relieving the stress during the high-temperature period.
The support grade slab used a control joint to control cracking on the surface and also help to raise the column.
2. Monolithic Slab on Grade
A Monolithic slab on grade, it does not have any traditional footing but this concrete slab is acting as a footing for the building, walls, and columns.
This type of grade on a slab foundation is framed by providing batter boards around the slabs. These batter boards help to identify slab corners because they act as a mold.
Grade on a slab is usually rested on the layers of bitumen (moisture barrier) and gravel, which is preventing the entry of water into the slab. The perimeter or edge of the slab on grade is thicker than the rest of the slab surface, this thicker portion works like a mini footing and also helps to distribute the overload on the large area of the ground.
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Advantages of Grade on Slab Home
The Advantages of Grade on slab home are listed below,
- Grade on a slab is an inexpensive competitively doing a crawl space under a structure or a full basement under a structure.
- Grade on a slab is sturdy, the building or structure is directly resting on the poured concrete and it does not rely on the supports and beams to sustain the building.
- Slab-on-grade foundations are excellent for flooring in garages, barn, and shed.
- The grade on the slab foundation does not have a termite attack problem.
- In Grade on slab foundation excavation cost, labor cost and forms are at a minimum.
- Construction speed is high.
Disadvantages of Grade On Slab
The Disadvantages of Grade on the slab are listed below;
- Grade on a slab foundation in a high chance to settle down the foundation.
- The grade on a slab is creating a problem when extending the building.
- Difficult to check the lines periodically.
- In Grade on slab does not have an access to utility lines such as gas lines, pipelines, cable, etc
- Slab on grade is located in low profile elevation so a high chance to flood even in moderate rains.
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Slab On Fill vs Slab On Grade
The difference between Slab On Fill vs Slab On Grade is as follows,
| Slab On Fill | Slab On Grade |
| Slab on Fill is also known as Concrete slab. It is one type of grade on a slab. | A slab on grade is also known as a Floating slab foundation. |
| The slab on the fill layer is made up of a mixture of broken stones, masonry, and concrete. | Slab on Grade is made up of a layer of Bitumen and gravel. |
| It is built over soil or aggregate layer. | Built-in a grade surface or slightly dug in. |
Slab on Grade Foundation vs Crawl Space
The difference between slab on grade vs crawl space foundation is as follows,
| Slab on grade foundation | crawl space |
| The slab on the grade foundation is raised slab that the house is built over it. | A crawl space foundation is a concrete wall that exterior support the interior walls and beams. |
| Construction of slab on grade foundation is inexpensive. | Construction of Crawl space is more expensive. |
| Construction takes a shorter time. | Construction takes a longer time. |
| Slab on grade foundation is more energy efficient. | Crawl space is less energy efficient |
| The slab on the foundation is not suitable for flood-prone areas. | Crawl Space is good for flood-prone areas. |
| Slab on grade is less accessible for gas lines, Plumbing lines, and cable lines. | Crawl space is more accessible for gas lines, Plumbing lines, and cable lines. |
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