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Footing Size Formula:
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Deck footing size calculation determines the appropriate foundation size needed to support a deck structure based on the load it will bear and the soil's bearing capacity. Proper footing sizing is essential for structural integrity and safety.
The calculator uses the following formula:
Where:
Explanation: The formula calculates the required footing area by dividing the total load (area × load per sq ft) by the soil's capacity to bear weight.
Details: Correct footing sizing prevents deck settlement, ensures structural stability, meets building code requirements, and provides long-term safety for deck users.
Tips: Enter tributary area in square feet, load in pounds per square foot (psf), and soil capacity in psf. All values must be positive numbers. Consult local building codes for specific requirements.
Q1: What is tributary area?
A: Tributary area is the portion of the deck that each footing supports, typically calculated by dividing the total deck area by the number of footings.
Q2: How do I determine soil capacity?
A: Soil capacity is determined through soil testing. Typical values range from 1,500-4,000 psf for different soil types, but professional assessment is recommended.
Q3: What loads should I consider?
A: Consider dead loads (deck weight), live loads (people, furniture), and environmental loads (snow, wind). Building codes typically specify minimum requirements.
Q4: Are there minimum footing size requirements?
A: Yes, most building codes specify minimum footing dimensions regardless of calculated size. Common minimums are 12" diameter or 12"×12" square footings.
Q5: How deep should footings be?
A: Footings should extend below the frost line to prevent frost heave. Depth requirements vary by climate region and local building codes.