3.6 FOOTINGS & SLABS

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FOOTINGS & SLABS

Confirm that the layout is completely square.
  1. One way to check is to diagonally measure from one corner to the other; the distance should be equal for both diagonal measurements. If not, adjust until they become equal. Once they are equal the corners will be 90°.
  2. Another way is to use the Pythagorean Theory - (a2 + b2 = c2). This 2. theorem calculates the hypotenuse using A & B. Many construction calculators incorporate this method.
  3. Another method involves the 3-4-5 right angle principle. 90°angles 3. are obtained with any multiple of 3-4-5.
  4. The easiest way is to use a laser level that shoots a right angle.

Footings:

1. Footings are designed to distribute structure loads and should be poured on undisturbed native soil or compacted materials

2. The size of the footing is determined by numerous factors such as soil conditions, seismic zoning, loads, number of stories and water tables. Check with your local building official, engineer or architect.

3. Ensure that the footings/slabs are as level as possible, ideally within ¼ inch ± all around. This will reduce the amount of adjusting you will need to do when laying the first course. Minor adjustments can be made by trimming or shimming the blocks.

4. For ease of installation, it is recommended that any required step footing be calculated to the height of the block.

5. Place footing dowels according to local building codes, engineering and plan specifications. Often, vertical rebar are inserted in the wall throughout the entire structure to align vertically with the footing/slab dowels. Dowels usually extend out of the footing between 12 and 30 inches. It is beneficial for later vertical rebar placement to indicate on the footing/slab where the dowels are. This can easily be accomplished with some chalk or marking paint.

SAFETY NOTE: cap the dowels once they are installed in the footing or slab.

6. Footings/slabs should be clean of foreign material and dirt wherever block is to be laid.

7. While the walls are constructed be sure to keep the form cavities free from any foreign materials. Foreign materials that fall through the forms to the footing or slab can be removed in several different ways depending on what it is

  • Snow – cut small weep holes along the bottom course and melt with water
  • Small amounts of dirt can easily be blown out
  • Large amounts of dirt can be washed out
  • Tools – Cut an access hole, remove object(s), replace EPS, glue in place, support area with 1x2 or plywood/osb.

Guides and Layouts:

  1. Snap chalk lines on the footing/slab to mark where the inside, outside, or both sides of the blocks will go
  2. Mark sides of door and window openings on the footing/slab so you remember to cut them out as you build
  3. Be sure to include the buck dimensions
  4. See window/door buck layout requirements

TIP: You can mark where doors go on slab/footing and mark where windows go later on the lower block courses.
  • Mark the footing/slab where the dowels rise out of the footing/slab
  • Enables you to drop vertical rebar in same area later

TIP: It can be helpful to place a small ring of PVC pipe around each dowel. This provides a “catch” for the vertical rebar after the wall is built, ensuring each dowel is aligned properly with the rebar.