The following procedure details the construction methodology for a crawl space foundation:
A foundation that provides a crawl space under the floor can be constructed in two different manners:
- A concrete footing can be poured independent of the wall and then a foundation wall of concrete block can be laid on top of the footing, as shown in Figure 1.
Figure 1 - Concrete block laid on concrete footing
- The footing and the wall can both be poured in concrete, as shown in Figure 2.
Figure 2 - Poured concrete footing and wall
- The footing should always be constructed of concrete.
- It should be at least 1 foot below the frost line. Check with your local building department for their specific footing criteria.
- The width of the footing should be twice the thickness of the wall. Hence a wall that is 8 inches thick would have a footing that is 16 inches wide and when the wall is constructed or poured the footing should be protrude an equal distance on both sides of the wall. In our example, the footing would protrude 4 inches on both sides of the wall.
- The height of the footing should be the same dimension as the width of the wall. Hence a wall that is 8 inches thick would have a footing that is 8 inches high.
- If you are pouring a concrete wall, a keyway, as shown in Figure 3, should be left in the footing so that the concrete wall will not slip due to ground water or earth backfill pressures. The keyway is generally made 1/2 the wall thickness at the top and 1/3 the wall thickness deep, with sloping sides and is centered on the footing.
- You can create a footing trench, and allow the earth walls of the trench to act as the forms. To ensure that you maintain a proper elevation grade stakes are inserted inside the trench.
- You can use boards to create a form for the footing in the same manner as you would when forming a concrete slab.
- Do not commence constructing a block wall or pouring a concrete wall until the concrete footings have properly cured.
- The top of the wall, block or concrete should be at least 18 inches above finished grade to allow access to the crawl space, ventilation and installation and repair of plumbing and electrical services.
The footing can be poured in 2 manners:
In both cases, rebar reinforcing as previously described should be used in the footings.
The following procedure details the construction methodology for a basement wall foundation, as shown in Figure 4:
If you require a basement in your new home or addition, you must construct the foundation with extreme care. Basement walls are subjected to a great deal of pressure from ground water and soil. If it is your intent to have a basement that is not damp you must construct it properly.
Figure 4 - Construction of poured concrete basement footing, floor, wall and drainage
To properly construct your new basement you must:
- Install drainage or weeping tiles on top of the footing on the outside of the new foundation wall. Drainage tiles have holes in the pipe which collect water as it passes through the soil and gravel. The tile should be installed in a bed of gravel or crushed stone and should drain into a dry stream bed or storm sewer. The gravel is necessary to prevent the drainage tiles from clogging.
- The outside of the wall should be parged or covered with a mixture of masonry cement, mopped with hot asphalt or covered in polyethylene. A layer of Styrofoam insulation may be added to the outside of the foundation wall to prevent heat loss.
- Grade the property so that all surface water and gutter downspout water will flow away from the foundation. It may be noted that as the area where the foundation is built is generally excavated land, the backfill that is put back after the footing and foundation wall have been constructed will most likely settle over time. It is important that additional soil be added against the lower part of the foundation wall to ensure that water flows away from the foundation.