1. Foundations Slab & Crawl Foundations
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Crawl Foundations
Slab Foundations

2. Slab Foundations Ardrey Kell High School Charlotte, NC
Drafting 2 (Architecture)
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3. Slab Foundations
A minimum 4” thick foundation that incorporates a concrete base poured over the ground that creates the first floor of a home.
There are (2) types of slabs commonly used in residential construction:
Stem Wall Slab
Monoslab.
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4. Concrete slab built with a masonry foundation wall
Slab Foundations
Slab Foundations are the most common, and least expensive type foundation built.
Put simply, slabs are concrete that is poured over the ground, and contained within forms, or walls. The slab serves as the floor of the building while at the same time anchoring the building to the ground.
Slabs must be built on relatively flat lots.
The concrete is usually poured 4” thick, and thicker under the walls.
Concrete slab built with a masonry foundation wall
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5. Slab Foundations
The diagram at left shows a sectional view of a stem wall slab foundation.
Notice how the footing extends well below the surface, and is reinforced with “rebar” which is a term used to describe reinforcement bar.
Rebar is made of steel and adds tensile strength to the footings and foundation.
Rebar is required because concrete is very weak in tension, and will crack and fail without it.
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6. Slab Foundations Plumbing & Electrical utilities must be
located and installed in
the slab prior to
pouring the concrete.
The picture at right shows a slab with the utilities located and protected from the upcoming concrete pour.
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7. Slab Foundations
To correct a mistake in locating a utility in a slab means big $$$ in repairs!
Slabs must be broken with a jack hammer, or cut with a concrete saw to repair.
Dust, noise, delays in production, customer dissatisfaction, and labor all figure into the total cost of making a mistake in properly locating utilities.
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8. Slab Foundations
As discussed earlier, slab Foundations must be reinforced with steel mesh and / or rebar in order to prevent the concrete slab from cracking.
Steel reinforcement bars add tensile strength to the concrete floor.
Remember; rebar is used to increase the tensile strength of concrete.
WELDED WIRE MESH
REBAR
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9. Slab Foundations
Tensile Strength is the resistance a material has to being pulled apart.
Concrete is very strong in compressive strength. This means it easily resists being crushed. This what makes it a great material for foundations and roadways.
By adding rebar, concrete becomes remarkably strong in multiple conditions, and serves many construction purposes.
Concrete will be poured over this rebar cage and will create an extremely strong wall
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10. Slab Foundations
The concrete used in slab construction is often reinforced with tiny pieces of fiberglass called “fibermesh.”
“Fibermesh” is added to concrete mixtures while they are being mixed at the concrete factory, and delivered by truck to the jobsite.
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11. Slab Foundations
Cracks in a slab are frequently caused by the settlement of soil under a concrete slab.
Soil settlement is usually a result of building over “expansive soil” or improper soil compaction prior to construction.
Expansive soil (known as “bull tallow” in North Carolina) shrinks and expands with changes in moisture content and temperature.
Reinforcement Bar (Rebar) helps prevent slab cracks when foundations are built over expansive soil.
Rebar
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12. Slab Foundations
Pouring a large slab foundation is usually done with a concrete pump.
The pump allows workers to work at long distances from the mixer without having to use wheelbarrows to transport the concrete.
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13. Slab Foundations
Smaller slabs are usually poured with only the use of a concrete mixer, wheelbarrows and a small crew of workers.
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14. Slab Foundations
Often nothing more than simple hand tools are used to finish the “flatwork” of a building.
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15. Slab Foundations
Mechanical floats and other automatic devices are used in many situations.
(Mainly commercial construction and large residential jobs)
Power Concrete Float
(Walk Behind)
Power Concrete Float
Power Concrete Agitator
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16. Slab Foundations
Review:
Less expensive to build than most other type foundations.
Must be built on flat lots.
Concrete usually poured 4” thick
Forms or foundation walls are required to hold the concrete in place while it cures.
Concrete must be reinforced with steel and / or fibermesh to prevent cracking.
Concrete may be “finished” using hand tools or power equipment.
Concrete hardens under a process called hydration.
The water in concrete does not evaporate, but actually becomes a part of the concrete. This is why concrete can harden while submerged in water.
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17. Ardrey Kell High School Charlotte, NC Drafting 2 (Architecture)
Crawl Foundations
Ardrey Kell High School
Charlotte, NC
Drafting 2 (Architecture)
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18. Foundations
The foundation of a house is a system of masonry and wood products that are used to perform the following tasks:
Provide support to the house to keep it from sinking.
Hold the house to the ground to prevent it from moving due to wind, seismic or other forces.
Provide a surface for the first floor of the building.
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19. Crawl Foundations
A crawl foundation consists of a masonry wall built on top of a reinforced concrete footing. This type foundation contains pilasters and piers that support girders that in turn support the floor system of the house.
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20. Crawl Foundations
Crawl foundations may be built on almost any lot, however they are most often built on gently sloping lots.
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21. Crawl Foundations
Crawl foundations are simple to build and one of the most common types of foundations built.
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22. Crawl Foundations
To begin construction of a crawl foundation, it is first necessary to dig footings and fill them with reinforced concrete. These footings will work to spread the load of the building over a large area.
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23. Crawl Foundations
Once the footings have been poured and have cured, masonry walls are built on top of the footings. Usually the foundation walls are built to a height of around two feet.
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24. Crawl Foundations
PIER
Pilasters and piers are added to the center of the foundation. These items are used to support girders and concentrated loads on the foundation.
PILASTER
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25. Crawl Foundations
Once the foundation walls and piers are complete, the wood framed floor system is attached to the masonry foundation wall.
FLOOR JOIST
GIRDER
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26. Crawl Foundations
The actual connection between the foundation wall and the wood part of the floor system is via a mud sill. The mud sill is a treated 2x6 laid flat on the foundation wall, and held down by anchor bolts or straps.
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27. Crawl Foundations
A termite shield is placed between the wooden part of the structure and the masonry foundation wall to prevent termite infestation.
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28. Crawl Foundations
A drain tile is also placed around the perimeter of the foundation wall. The drain tile is used to carry surface water away from the foundation of the house.
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29. Crawl Foundations
Once the foundation wall is completely built, soil is backfilled against the outside of the foundation wall in order to level the ground around the house.
Soil next to a house must be graded away from the house so that water will drain away from the foundation wall.
International Building Code requires that the grade slope away from the foundation at a rate of 6” per ten feet of distance from the wall.
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30. Crawl Foundations
There are a number of advantages and disadvantages of to crawl foundations.
Advantages Include:
Ease of construction
May be relative low cost
Create nice home elevations
Easy access to utilities and mechanical systems (HVAC)
Disadvantages
Moisture Buildup under the house
Toxic Mold buildup
High crawls expensive to build
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31. Crawl Foundations
Sometimes Sump Pumps and French Drains are required to keep moisture from building up under a crawl space.
The water is captured in perforated pipes and transported to a reservoir which contains a pump that purges the water from under the house.
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32. Crawl Foundations
Sealing crawl spaces is a relatively new idea. By sealing a crawl space, moisture is controlled, and therefore, the mold problem is eliminated.
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33. Crawl Foundations
In addition, sealed crawl spaces provide a healthier home environment as radon gas and other toxic gasses/odors are prevented from being introduced to the indoor environment through “chimneying.”
“Chimneying” is a term used to describe how the air in a crawl space enters the main living portion of a structure through the floor.
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