Building foundation footings

The footings play a specific load-bearing role inasmuch as they support the weight of the building, whether the building rests on rests on posts or walls which in turn rest on the footings. In planning footings, be sure to consider the type of soil in which they will be poured (clay, marshy etc.). At the very least, footings must be poured below the frost line.
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Depth of footings
Type of footings
Excavation and formwork
1. Assemble the formwork
2. Dig a trench
3. Mould the keys
4. Insert the reinforcing bars
5. Prepare for the garage drain
6. Chose the right concrete
7. Prepare the pouring
8. Spread the concrete
9. Install the wooden pieces
10. Let it dry
11. Backfilling

Depth of footings

Concrete footings must rest on firm soil and extend below frost line. Build footings on lightly moist soil (be sure that soil is not wet). National and local building codes indicate footing depth; ask your local building department (example: Montreal: 4' 1/2").

Type of footings

Flat surface footing is used when the foundation wall is made of concrete blocks or cast concrete. It is possible to make a groove in the footing to hold the foundation concrete. Just insert the edge of a 2'×4' on top of the footing and remove as soon as the concrete has hardened.

Pier foundations (12" diam.) are used as foundation or footing without any other support. They are evenly spaced around the building's perimeter according to the local building codes. Dig a hole to install the 'Sonotube' and fill with concrete.

Excavation and formwork

Excavation: place stakes to indicate footing area. Remove lines from batter boards. Keep the area free from debris and dirt.

Formwork: double-headed nails are easier to remove than ordinary nails. Nail them into the stakes down to the formwork. Oil formwork surfaces touching concrete with waste crank-case oil.

Footing formwork: after digging, replace lines on batter boards and relocate the corners. Mark their location with stakes at the bottom of the excavation. Then drive levelling stakes along footing lines even with corner stakes.

1. Assemble the formwork

Having excavated the site, you can now assemble the formwork for the footings. Footings should be 30" (76,2 cm) wide and 10" (25,4 cm) high. They must be built in such a way as to allow for the centring of the walls in due course.

In order to determine exactly where you want to build the footings, you must first drive retaining stakes into the ground with the help of a sledgehammer. Then nail 2'' × 10'' (5,08 cm × 25,4 cm) boards to the stakes, one behind the other, to build the formwork.

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While you are at it, do not forget to build footings for steel posts, fireplaces and masonry chimneys as well as for the main foundations, in keeping with your plan. When the time comes to pour the concrete, you will need to insert bolts into the footings. They will be used later to secure posts.

2. Dig a trench

Before pouring the concrete, dig a trench through which you will run water intake, drainage and sewage pipes under the foundations to connect them to public utilities. Avoid digging this trench in corners with particularly heavy load-bearing responsibilities. When the installation of the required pipes is complete, cover the trench with machine-compacted gravel or with a light coat of concrete.

3. Mould the keys

Then prepare pieces of 2'' × 4'' (5,080 cm × 10,16 cm) wood that will be used to mould the keys into the footings. The keys increase the resistance of the wall to pressure from the soil and effectively prevent water infiltration between the footings and the foundations. In preparing the wood, be sure to cut it so the sides slope slightly, eventually forming a lozenge-shaped groove or key.

4. Insert the reinforcing bars

Insert two concrete reinforcing bars, 1/2" (1,270 cm) in diameter, inside the formwork. The bars should rest on 1-1/2" (3,810 cm) wood supports and be tied to them with metal wire.

5. Prepare for the garage drain

Now is the time to prepare the footings so you can insert the pipe leading to the garage drain. To do this, cut a length of PCV pipe, 6" (15,24 cm) in diameter, equal to the width of the footings formwork.
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