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close this book Self - Help construction of 1-story buildings
close this folder Detailed planning for construction
close this folder Planning foundations
View the document Footings
View the document Foundation walls
View the document Deciding upon the materials and dimensions for foundations
View the document Drawing final foundation plane

Foundation walls

The foundation walls can be made of rock, or they can be made of blocks of concrete, sand-cement, or stabilized earth.

All of these materials are strong enough to support the walls and roof of most 1-story buildings. The choice depends on what materials are available, the builders' budget, and whether or not earthquakes or severe weather conditions will require reinforcement in the foundation.


Foundation walls

 

Rock Foundation Walls. A rock foundation wall is built by setting stones that are 20 to 40 cm. long in mortar. The rocks must be cleaned so that no rocks remain on them. All the spaces between the rocks must be filled with mortar (these spaces are called "joints"). In addition, and most important, they must be laid so they overlap. If a straight line can be drawn between the rocks from the top to the bottom of the wall, a crack will develop.

Rock foundations are the least expensive to build. However, they require a large number of rocks, and it is difficult to clean, level, and overlap the rocks properly.

If the building position is on rocky ground, or on dry, well-packed clay soil, the footing for a rock foundation wall should be 4 to 8 cm. thick.

In less stable soils, such as sand, or gravel, the footing should be at least 10 cm. thick. In soft black soil, drained marshland, and made earth, the footing should be reinforced and should be 10 cm. thick.

In rocky or hard-packed clay soil, rock foundation walls need only be 30 cm. deep. In other soils, they should be at least 45 cm. deep.

Rock foundation walls should be at least 30 cm. thick, and they will be much more stable if they are flared at the base to 45 cm.

Block Foundation Walls. Whether built of concrete, sand-cement, or stabilized earth, block foundation walls are made by laying level rows of blocks on concrete footings until the wall reaches the planned height of the floor. Each row of blocks, called a course, is joined by mortar, as are the ends of each block.

Block foundations cost more to build than rock foundation walls (except in areas where the rock must be transported over large distances), but block foundation walls can be put up faster, and they are easier to build well.


Block foundation walls

 

In rock or firm clay soil, a block foundation should be 45 to 60 cm. deep. In less stable soil, a block foundation should NOT be used.

The width and thickness of the footing depend on the size of the blocks being used. In general:

• the footing should be as thick as the blocks are wide;

• the footing should be 3 times as wide as the blocks.


The footing should be 3 times as wide as the blocks.

 

Frost Line. The frost line is the depth to which the ground in any area freezes in the winter. In climates with freezing temperatures, the footing must be entirely below the frost line.

The table below gives suggested depths to be safely below the frost line in different climates:


Frost line

Lowest Temperature in Winter, Degrees Celsius

Safe Minimum Depth for Top of Footing

-1

45cm.

-5

75cm.

-11

90cm.

-18

1.05m.

-22

1.20m.

-28

1.30m.

Sloping Ground. If a building is built at an angle on a slope, it will tend to slide downhill, causing the foundation and walls to slip and/or crack. Thus if the ground under a building slopes or is uneven, the trenches for the foundation footing must be completely levelled.


Sloping ground

 

If the ground slopes sharply, it may be easier, or necessary, to "step" the trenches. When block foundation walls are planned, it's important to make each step the height of one or two courses of blocks.


Important to make each step the height of one or two courses of blocks