{
  "slug": "snow-load-roof",
  "title": "Snow Load on Roof Calculator",
  "heading": "Roof Snow Load Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/snow-load-roof",
  "summary": "Estimate ground and roof snow load in psf to check against your roof's rated capacity.",
  "description": "Snow load is measured as weight per square foot, not depth, because snow density varies enormously — fresh powder runs about 7-10 lb/ft³ while wet, settled, or rain-soaked snow can exceed 20 lb/ft³. This calculator estimates load from snow depth and a density you select (or measure directly with a scale and known-volume container), then applies the standard roof exposure and thermal factors used in ASCE 7 snow load calculations to convert ground snow load to roof snow load. Most residential roofs are designed for 20-40 psf depending on region; if your estimated load approaches or exceeds your roof's rated capacity, that's a signal to shovel or call a structural engineer, not a DIY judgment call.",
  "formula": "Load (psf) = depth (ft) × density (lb/ft³); roof snow load = ground load × 0.7 (exposure) × thermal factor × importance factor.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=snow-load-roof",
  "inputs": [
    {
      "id": "depth",
      "label": "Snow depth",
      "kind": "number",
      "hint": null,
      "default": 18,
      "unit": "in",
      "min": 1,
      "max": 120
    },
    {
      "id": "snowType",
      "label": "Snow type",
      "kind": "select",
      "hint": null,
      "default": "18",
      "options": [
        {
          "value": "8",
          "label": "Fresh powder (~8 lb/ft³)"
        },
        {
          "value": "15",
          "label": "Settled/packed (~15 lb/ft³)"
        },
        {
          "value": "18",
          "label": "Wet snow (~18 lb/ft³)"
        },
        {
          "value": "25",
          "label": "Rain-soaked/ice-heavy (~25 lb/ft³)"
        }
      ]
    },
    {
      "id": "capacity",
      "label": "Roof rated capacity",
      "kind": "number",
      "hint": null,
      "default": 30,
      "unit": "psf",
      "min": 10,
      "max": 100
    }
  ],
  "outputs": [
    {
      "id": "roofLoad",
      "label": "Estimated roof snow load",
      "format": "number",
      "hint": null,
      "primary": true
    },
    {
      "id": "groundLoad",
      "label": "Ground-equivalent load",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "pctOfCapacity",
      "label": "% of rated roof capacity",
      "format": "percent",
      "hint": null,
      "primary": false
    },
    {
      "id": "status",
      "label": "Status",
      "format": "raw",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Snow depth: 18 in",
      "Snow type: Wet snow (~18 lb/ft³)",
      "Roof rated capacity: 30 psf"
    ],
    "outputs": [
      "Estimated roof snow load: 18.9",
      "Ground-equivalent load: 27",
      "% of rated roof capacity: 63%",
      "Status: Monitor closely"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter snow depth (in).",
      "Enter snow type.",
      "Enter roof rated capacity (psf).",
      "Read your estimated roof snow load on the right — it updates as you type.",
      "Hit Share to keep the scenario or send it to someone."
    ]
  },
  "scenarios": [
    {
      "name": "Conservative",
      "description": "Lower-end numbers — what if things land soft?",
      "values": {
        "depth": 11,
        "snowType": "18",
        "capacity": 20
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "depth": 18,
        "snowType": "18",
        "capacity": 30
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "depth": 29,
        "snowType": "18",
        "capacity": 50
      }
    }
  ],
  "limitations": [
    "Estimates assume standard, average conditions — local rules, pricing, and materials vary.",
    "Results are rounded for readability; add a buffer before ordering, booking, or committing.",
    "Double-check anything with a real cost attached against a local quote."
  ],
  "faq": [
    {
      "q": "Why is roof load estimated as only 70% of ground snow load?",
      "a": "Wind exposure on roofs sheds and redistributes snow that would otherwise accumulate on the ground, so building codes (ASCE 7) apply an exposure factor, typically around 0.7 for a fully exposed roof, before further adjusting for thermal and building-use factors."
    },
    {
      "q": "How do I find my roof's actual rated capacity?",
      "a": "Check building plans or permits for your local snow load requirement, usually stated in your jurisdiction's building code adopted from ASCE 7 tables; older homes may have been built to lower legacy standards, so when in doubt have a structural engineer verify it."
    },
    {
      "q": "Why does wet snow matter so much more than fresh powder at the same depth?",
      "a": "Wet or rain-soaked snow can be 2-3 times denser than fresh powder at identical depth, meaning an 18-inch wet snowpack can weigh as much as a 45-50 inch powder snowpack — depth alone is a poor predictor of structural risk."
    },
    {
      "q": "What are warning signs my roof is overloaded right now?",
      "a": "Sagging ceiling tiles, new cracks in drywall near roof lines, doors or windows that suddenly stick, popping or cracking sounds, and visible roof deflection when viewed from outside are all signs to evacuate the area below and call a professional immediately."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/wind-pressure-on-wall",
    "https://www.revenuelab.fyi/toolbox/roof-rainwater-harvest"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Snow Load on Roof Calculator (https://www.revenuelab.fyi/toolbox/snow-load-roof)"
}