Deck Footing Size Calculator

Formula

To calculate the size of the deck footing:

\[ F = \frac{W \times L \times D \times C}{S \times B} \]

Where:

\( F \) is the size of the deck footing (sq ft)
\( W \) is the width of the deck (ft)
\( L \) is the length of the deck (ft)
\( D \) is the depth of the deck footing (ft)
\( C \) is the soil bearing capacity (psf)
\( S \) is the allowable soil bearing capacity (psf)
\( B \) is the safety factor

What is a Deck Footing?

A deck footing is a crucial structural element that provides the foundation for a deck. It is typically made of concrete and is buried into the ground, acting as a base for the deck’s support posts. The footing is designed to distribute the weight of the deck and prevent it from sinking or shifting, which could lead to structural instability. The size and depth of the footing depend on the size and weight of the deck, the type of soil, and local building codes. It is essential to install the footing correctly to ensure the longevity and safety of the deck.

Example Calculation

Let's assume the following values:

Width of the Deck \( W \) = 20 ft
Length of the Deck \( L \) = 15 ft
Depth of the Deck Footing \( D \) = 3 ft
Soil Bearing Capacity \( C \) = 1500 psf
Allowable Soil Bearing Capacity \( S \) = 2000 psf
Safety Factor \( B \) = 1.5

Step 1: Multiply the width, length, depth, and soil bearing capacity:

\[ W \times L \times D \times C = 20 \times 15 \times 3 \times 1500 = 1350000 \]

Step 2: Multiply the allowable soil bearing capacity by the safety factor:

\[ S \times B = 2000 \times 1.5 = 3000 \]

Step 3: Divide the result from step 1 by the result from step 2:

\[ F = \frac{1350000}{3000} = 450 \text{ sq ft} \]