Deck foundations

You are about to undertake the construction of a one or two level patio. You must then decide what type of foundation is best for your plan taking into consideration your needs and your budget. The various steps related to each type are also described below to help you choose the right type.

There are four types of foundations for your deck. However, from the standpoint of construction stability, we suggest you build a foundation with footing.

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1. Concrete pillars with footings
2. Concrete pillars without footings
3. Dek-Blocks
4. Screwable foundation posts

1. Concrete pillars with footings

Concrete pillars with footings are, without a doubt, the most stable type of foundation you can use. The advantage of sills is that they solidly stabilize the concrete piers that are attached to them. However, this technique is rarely used because of the extensive excavation work involved. A large area must be excavated in order to place the formwork below the frost line. This work requires the use of a mechanical digger.

You could also use prefabricated circular bases that adjust to 8 in. (203 mm), 10 in. (254 mm) or 12 in. (305 mm) diameter pier tubes into which concrete is poured. These may be inserted into the holes without excavating the entire perimeter of the deck, but since the diameter of the hole to be dug must be at least 18 in. (457 mm), a mechanical digger would nonetheless be required.

1.1 

Dig out 4 in. (10 cm) of soil inside the perimeter.

1.2 

You need to calculate the weight of the terrace in order to decide on the number of pillars required. If you have drawn your own plan, you may need to consult an expert to determine that. Then, determine the location of the pillars.

1.3 

If you're planning to build the terrace at the same time as the house, have both foundations dug at the same time. That will make it easier for you to install formwork (54 in./137 cm deep) and pour the concrete.

* If your terrace is an addition, it will be easy for you to dig 54 in./137cm-deep holes using a posthole digger. In such cases, use pre-fabricated circular footings which adapt to circular forms of varying diameters and in which you will pour the concrete.

1.4 

Using 2 in. × 8 in. (5 × 20 cm) boards, build square forms work (24 in./61 cm), 8 in. (20 cm) deep. Lay in a reinforcing rod (diagonally) and add wire mesh.

1.5 

Stand an L-shaped reinforcing rod in the centre of the frame, placing the short end of it under the diagonal reinforcing rod. The L-shaped rod will serve as the link between the footing and the pillar. Hold it erect as your pour the concrete. Be sure to comply with the concrete manufacturer's instructions on curing time.

1.6 

Place tubular forms (Sonotubes®) on the centre of the footings and hold them up with pieces of wood. Use a level to ensure the tubes are vertically levelled.

1.7 

Nail the tube to the footing at a 45°, from the outside of the tube into the footing.

1.8 

Backfill the footing using the original soil. Use a long narrow object to slowly stir the concrete to the bottom of the tube, making sure the concrete remains homogenous and free of air bubbles. Before the concrete sets, insert, in the centre, the rods to which beam brackets will be attached later.
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