ladder-safety-planner

Use when setting up any ladder for home DIY — gutter cleaning, roof access, painting, light bulbs — and unsure what size or type you need. Computes correct stepladder/extension size from working height, 4:1 lean-angle geometry, duty rating (Type III–IAA) with gear allowance, roof-access overlap math, power-line clearances, and a pre-climb checklist. Fights the ~500k/yr US ER-treated ladder injuries with engineering rules, not vibes.

Overview

Ladders are the most dangerous tool most people own: roughly 500,000 ER-treated injuries and ~300 deaths per year in the US alone, almost all from falls under 12 feet. The failure is almost never the ladder — it is the setup: a stepladder two sizes too short (standing on the top cap), an extension ladder leaned at 30° instead of 75°, a Type III household ladder loaded with a 220 lb roofer plus a bundle of shingles, or aluminum set up under the service drop.

This skill replaces guessing with arithmetic:

1. Size selection — from the height you need to touch, pick the right stepladder size (stand no higher than 2 steps from the top; max reach ≈ size + 4 ft) or extension ladder length (3 ft above the roof line, minus section overlap).
2. 4:1 angle geometry — base distance = working height ÷ 4, plus a no-tape-measure phone check.
3. Duty rating — Type III (200 lb) → IAA (350 lb), computed from body + clothes + tools + materials actually carried.
4. Roof access — extension above roof edge, walk-up sequence, and the re-securing move people get wrong.
5. Power lines & material — clearance ladders by voltage; fiberglass near electricity, never metal.
6. Pre-climb checklist — the 60-second ritual.

When to Use

• Buying or borrowing a ladder for a specific job ("what size do I need to clean my gutters on a 2-story house?")
• Setting up an extension ladder against a wall or roof edge
• Deciding whether your old household stepladder is rated for you + gear
• Any work near overhead service drops or overhead lines
• Choosing between stepladder / extension ladder / ladder+platform for a task

Don't use for: scaffolding design, rope access, boom lifts or anything professional rigging — hire it out. Not a substitute for OSHA-compliant training on job sites.

Quick Start

bash

python3 scripts/ladder.py setup --reach 16 --type extension --purpose roof
python3 scripts/ladder.py setup --reach 9  --type step
python3 scripts/ladder.py angle --height 14
python3 scripts/ladder.py duty --weight 205 --gear 25
python3 scripts/ladder.py powerline --kv 0.4
python3 scripts/ladder.py checklist

Stdlib-only, no network.

Core Rules (what the math encodes)

Rule	Value	Why
Stepladder max standing	top 2 steps OFF-limits	Standing there removes handholds and inverts the tripod
Stepladder max reach	≈ ladder size + 4 ft	Assumes ~5'9" person with 12" vertical reach
Extension lean angle	4:1 (75°)	base out = climb height ÷ 4; shallower = slide-out, steeper = tip-back
Extension above roof edge	≥ 3 ft	A handhold rail when you step off/on the roof
Usable vs nominal length	16→13, 20→17, 24→21, 28→25, 32→29, 36→33, 40→37 ft	Sections overlap in the middle — the fly section doesn't add net length
Duty ratings	III 200 / II 225 / I 250 / IA 300 / IAA 350 lb	Rated load = you + clothes + tool belt + materials, all at once
Power lines	≥10 ft to 50 kV, more above	Aluminum and wet wood both conduct
3 points of contact	always	One hand or two feet — never carry loads up

Workflow

1. Define the reach — the highest point you must comfortably touch with your hands (for gutters: gutter height; for roof work: roof edge).
2. setup --reach H --type step|extension [--purpose roof] → recommended size, standing platform, and the setup geometry if extension.
3. Check the load path: duty --weight W --gear G → minimum duty type. Budget honestly: a drill + shingle bundle + bucket is 20–50 lb.
4. angle --height H for extension ladders → print the base distance and verify with the standing-toes / straight-arm check (below).
5. Scan overhead: powerline --kv V (residential service drop is usually 0.12–0.48 kV, but treat unknown as high). 10 ft minimum — that includes the ladder while it's being carried upright.
6. checklist — run the 60-second pre-climb ritual. For roof work, tie off or have a helper foot the ladder for the step-across.
7. For anything involving steep pitch, wet roof, or >24 ft reach: stop — rent a lift or hire a pro. This skill is for setup arithmetic, not risk appetite.

No-tape-measure angle check

Stand with your toes against the ladder rails, reach straight out parallel to the ground: your palm should just touch the rungs. Too far / can't touch = wrong angle; adjust the base.

Roof access sequence

1. Set ladder with 3 ft above the roof edge, base at height÷4.
2. Climb to just below roof level; check footing and roof condition.
3. Keep 3 points of contact; shift weight slowly to the roof, then grab the rail ABOVE the roof edge before fully stepping off.
4. Coming back: grab the rail above the edge BEFORE stepping back on — the ladder below you is now unsupported against your momentum.

Common Pitfalls

1. Buying by "house height" instead of reach. A 24 ft wall needs an extension ladder rated ~27+ ft usable (24 + 3 above roof edge if you step off) — not a "24-footer" whose usable length is only 21 ft.
2. Ignoring section overlap. A nominal 16 ft extension ladder extends to about 13 ft of safe length. The table in setup encodes this.
3. Standing on the top cap / top step of a stepladder because "I just need 6 more inches." That 6 inches is where half the injuries live — take the bigger ladder.
4. Lean angle by eye. Most people set ~60–65°, which slides out under dynamic load. Measure height÷4 or use the toes/straight-arm check.
5. Duty rating = "my weight." It's your weight plus everything on you. 200 lb person + 30 lb of paint + tools on a Type III is over.
6. Aluminum under the service drop. Fiberglass rails are the only non-conductive option near electrical; wet/fiberglass-dirty still needs distance. powerline gives the clearance table.
7. Leaning a stepladder closed against a wall. Stepladders are built to be self-supporting and spread; leaning one closed is an uncontrolled slide. Use the right tool.
8. Ladder feet on dirt/mulch/snow. Level, firm footing with both feet flat and levelers if needed; soft soil swallows one foot and rotates the whole setup.

Verification Checklist

• Reach defined as "highest point I touch", not wall height
• Recommended size accounts for standing-level limits (stepladder) or 3-ft extension + overlap (extension)
• Duty rating ≥ body + clothes + gear + materials
• Base at height÷4 (extension), verified with toes/straight-arm check
• Overhead lines checked with 10 ft+ clearance, fiberglass near power
• Feet level and on firm surface; 3 points of contact planned
• Helper informed or ladder secured/tied for roof step-off

Safety Disclaimer

Fall height is not a proxy for injury severity — most fatal ladder falls are under 10 feet. When the math says the setup is marginal, the correct tool is a rental lift or a professional, not confidence. Local codes and OSHA rules govern workplaces; this skill is for homeowner planning.