Please enter valid dimensions and post count.
Total Deck Area:
0 sq ft
Dead Load (Structure Only):
0 lbs
Live Load (Occupancy/Snow):
0 lbs
Total Load Capacity Required:
0 lbs
Estimated Load Per Footing:
0 lbs
function calculateDeckLoad() {
var lengthInput = document.getElementById('dw-length');
var widthInput = document.getElementById('dw-width');
var materialInput = document.getElementById('dw-material');
var scenarioInput = document.getElementById('dw-scenario');
var postsInput = document.getElementById('dw-posts');
var errorMsg = document.getElementById('dw-error-msg');
var resultsArea = document.getElementById('dw-results-area');
// Parse values
var length = parseFloat(lengthInput.value);
var width = parseFloat(widthInput.value);
var deadLoadPsf = parseFloat(materialInput.value);
var liveLoadPsf = parseFloat(scenarioInput.value);
var numPosts = parseInt(postsInput.value);
// Validation
if (isNaN(length) || length <= 0 || isNaN(width) || width <= 0 || isNaN(numPosts) || numPosts <= 0) {
errorMsg.style.display = 'block';
resultsArea.style.display = 'none';
return;
}
errorMsg.style.display = 'none';
// Calculations
var area = length * width;
// Dead Load = Area * Material Weight Factor (includes framing estimate)
// Note: deadLoadPsf comes from the select value
var totalDeadLoad = area * deadLoadPsf;
// Live Load = Area * Usage Factor
var totalLiveLoad = area * liveLoadPsf;
// Total Load
var totalLoad = totalDeadLoad + totalLiveLoad;
// Load per footing (Simplified average distribution)
var loadPerPost = totalLoad / numPosts;
// Update DOM
document.getElementById('res-area').innerHTML = area.toFixed(1) + " sq ft";
document.getElementById('res-dead').innerHTML = Math.round(totalDeadLoad).toLocaleString() + " lbs";
document.getElementById('res-live').innerHTML = Math.round(totalLiveLoad).toLocaleString() + " lbs";
document.getElementById('res-total').innerHTML = Math.round(totalLoad).toLocaleString() + " lbs";
document.getElementById('res-per-post').innerHTML = Math.round(loadPerPost).toLocaleString() + " lbs";
resultsArea.style.display = 'block';
}
Understanding Deck Weight Loads
When designing or renovating a deck, understanding the structural weight requirements is critical for safety and building code compliance. Deck loads are generally categorized into two specific types: Dead Load and Live Load.
Dead Load vs. Live Load
Dead Load refers to the weight of the deck structure itself. This is constant and permanent. It includes the weight of the materials used for the framing (joists, beams, ledger boards), the decking surface, railings, and fixed fixtures. Different materials have significantly different densities:
- Pressure Treated Pine: Standard framing material, moderately heavy due to moisture retention from treatment (~10 psf).
- Cedar/Redwood: Lighter softwoods, often used for decking boards (~8 psf).
- Composite: Dense synthetic materials that often weigh more than natural wood (~15+ psf).
- Hardwoods (Ipe): Extremely dense and heavy tropical hardwoods (~25 psf).
Live Load refers to the transient weight placed on the deck. This includes people, furniture, grills, planters, and environmental factors like snow. Most residential building codes require a deck to support a live load of at least 40 lbs per square foot (psf). However, if you plan to install a hot tub, large planters, or live in an area with heavy snowfall, you must calculate for higher loads (often 60-100+ psf).
Why Calculate Load Per Footing?
The total weight of your deck is transferred down through the posts into the concrete footings in the ground. If your footings are not wide enough or deep enough to handle the Total Load Capacity, the deck can sink (settle) unevenly, leading to structural failure. By dividing the total weight by the number of posts, you get an average load per footing, which helps determine the required diameter of your concrete piers.
Disclaimer: This calculator provides an estimate for planning purposes only. Always consult a licensed structural engineer and local building codes before construction.