A footing calculation determines the required surface area and concrete volume to safely support a structure's load without exceeding the soil's bearing capacity.
For a 20x20 foot deck, you will typically need 6 to 9 footings, depending on how your beams and joists are sized and whether the deck is freestanding or attached to your house.
To calculate a footing size, divide the total downward weight (dead load and live load) by the allowable soil bearing capacity. The resulting number is the minimum required surface area in square feet or square meters. Finally, calculate the dimensions (length, width, or diameter) from that area.
For a standard 10x10 attached deck, you will typically need 2 or 3 concrete footings. If your deck is attached to the house using a ledger board, the house supports one side, meaning you only need a single beam with 2 to 3 footings on the outside edge.
Improper Footing Depth
One of the most frequent reasons for a failed footing inspection is an inadequate footing depth. Building codes and standards specify minimum footing depths to ensure that the structure can withstand various environmental forces, such as frost heave and soil movement.
For a 6x6 post (which actually measures 5.5′′×5.5′′), a 12-inch diameter Sonotube is the industry standard and most widely recommended size. This allows for a 1-inch concrete buffer on all sides and easily accommodates the standard 6x6 post base or bracket.
Pouring concrete directly on dirt is not recommended. While the concrete will set, the soil's moisture and tendency to shift or erode will cause the slab to settle unevenly, crack, or buckle over time. For a long-lasting, durable pad, you must excavate the area and install a compacted gravel base first.
Mixing concrete yourself can be the cheaper choice for small projects. For larger jobs like driveways, slabs, or patios, delivery often wins. Hand-mixing takes much longer, and mistakes in mixing water or cement can weaken the final product. One cubic yard of concrete requires about 45 bags of 80-pound Quikrete.
Water is the most common enemy of concrete surfaces. When water penetrates the surface of concrete, it can cause it to crack and weaken. This is especially true in colder climates where water can freeze and expand, creating even more damage.
Whether footings need rebar depends on your local building codes, soil conditions, and the structure being built. While plain concrete footings can sometimes support simple, light structures, most load-bearing foundations, homes, and projects in high-wind or seismic areas require rebar to prevent cracking and structural failure.
A footing calculation determines the required surface area and concrete volume to safely support a structure's load without exceeding the soil's bearing capacity.
You can look up the recommended footing size, based on the size and type of house and the bearing capacity of the soil. As you can see, heavy houses on weak soil need footings 2 feet wide or more. But the lightest buildings on the strongest soil require footings as narrow as 7 or 8 inches.
Choose 2x10 if you want a firmer, less bouncy deck, or if your joists need to span further than 10 to 11 feet. Choose 2x8 if you are building a small, low-to-the-ground deck where joists span under 10 feet, or if you want to save money on lumber.
The 3-4-5 rule is a fundamental geometry technique (based on the Pythagorean theorem) used to ensure your deck frame forms a perfectly square 90∘90 raised to the composed with power90∘ corner. It works by making the side lengths of a triangle proportional to the numbers 333, 444, and 555.
Coca-Cola does three main things to concrete: it slows down the curing process (acts as a retarder), etches the surface to expose decorative aggregate, and removes tough stains. This happens because of the soda's high sugar content and phosphoric acid.
To recap, the most common mistakes in concrete construction include adding too much water, neglecting site preparation, improper reinforcement placement, inadequate finishing, insufficient curing, and overlooking environmental conditions. These issues weaken the mix and compromise long-term performance.
The 90-minute rule is a longstanding concrete industry guideline stating that ready-mixed concrete should be completely discharged from the mixing truck within 90 minutes from the time water is first added to the cement. This limit ensures the mixture remains workable and achieves its full structural strength.
A gravel sub-base provides essential drainage, prevents the concrete from wicking moisture directly from the earth, and ensures a stable, even foundation. Skipping this layer often results in uneven settling, moisture damage, and structural cracking over time.
Yes, pouring concrete directly on wet or muddy ground is highly risky and can ruin the slab. Excess moisture in the soil can be absorbed by the concrete mix. This dilutes the water-cement ratio, drastically weakening the concrete, and also leads to uneven settling and major cracking.
Without gravel, the soil underneath can shift or settle over time—especially after heavy rain. This leads to pavers becoming uneven, causing tripping hazards and unsightly dips or humps in your patio or walkway.
If stripping is required, strip the form as soon as possible after the concrete has set to prevent concrete from sticking to the form. Recommended time for the easiest and fastest stripping is 24 to 48 hours after the pour. Sonotube concrete forms should not be left on the column for more than five days.
For standard fences and lighter structures, bury a 6x6 post at least one-third of its total length underground. For example, a standard 8-foot post requires a hole 30 to 36 inches deep (burying 2 to 2.5 feet, plus 6 inches of gravel for a drainage base).