Planning & safety
Ladders and roof safety: the 4:1 rule and when not to go up
Falls from roofs and ladders are among the leading causes of construction deaths. Most of the rules that prevent them are simple; the first one is knowing when not to climb.
The first rule: most jobs do not need the roof
Measuring a roof, judging its condition and estimating materials can all be done from the ground: measuring a roof from the ground shows how. Gutters, drip edge and the first course can be worked from a ladder. The roof surface is for roofing, by people equipped for it. OSHA’s construction statistics consistently put falls among the leading causes of worker deaths, and roofs and ladders are where many of them happen.
Choosing the ladder
An extension ladder is longer than the wall it leans on, longer again because it must extend above the roof, and shorter than its label because its sections overlap.
| Ladder size | Reaches extended (after overlap) | Eave height it serves, stepping off |
|---|---|---|
| 16 ft | about 13 ft | up to about 9½ ft |
| 20 ft | about 17 ft | up to about 13½ ft |
| 24 ft | about 21 ft | up to about 17½ ft |
| 28 ft | about 25 ft | up to about 21 ft |
| 32 ft | about 29 ft | up to about 25 ft |
A 20-foot eave
- Working length: 20 × 1.031 = 20 ft 7 in
- In use, with 3 ft above the eave: 23 ft 7 in
- A 24-ft ladder reaches only about 21 ft; a 28-ft ladder reaches 25 ft
- Base 5 ft from the wall
From the ladder length calculator. The eave height is the fascia figure from the ridge height calculator, or a tape from the ground.
Choose a duty rating for the person plus the load: Type I (250 lb) or Type IA (300 lb) for roofing, not a Type III household ladder. Use fiberglass anywhere near overhead power lines.
Setting it up
OSHA’s ladder rules for construction (29 CFR 1926.1053) translate directly to home use:
- The 4:1 angle. The base sits one foot out for every four feet of height to the support point, about 75 degrees. The quick check: toes at the ladder’s feet, arms straight out, palms on a rung.
- 3 feet above the landing. When the ladder is used to get onto a roof, its side rails extend at least 3 feet above the edge, or the top is secured with a grab rail.
- Secure top and bottom. Tie the top off to a fixed point or use a stand-off that bears on the roof rather than the gutter; stake or block the feet on soft ground, and use levellers on slopes.
- Three points of contact while climbing, facing the ladder, nothing carried in the hands; hoist tools and bundles separately.
- Step off straight, through the rails, never sideways past them, and never from above the top support.
- Ten feet from power lines, ladder and person.
- Never stand on the top three rungs of an extension ladder.
On the roof: fall protection by pitch
| Pitch | Walkability | Protection |
|---|---|---|
| Up to 4/12 | walkable | Dry, clean surface; anchor and harness strongly advised |
| 5/12 to 6/12 | walkable with care | Anchor and harness |
| 7/12 to 9/12 | steep | Roof jacks and planks, anchor and harness, rope grab |
| 10/12 and up | very steep | Staging; a job for professionals |
OSHA treats a roof steeper than 4/12 as a steep roof for fall protection in construction, requiring guardrails, safety nets or personal fall arrest systems. A personal fall arrest system is a roof anchor fastened through the sheathing into a rafter, a lifeline, a rope grab and a full-body harness, set up before work starts and used by everyone on the roof. The pitch calculator tells you which band a roof is in, and roof pitch explained covers the numbers.
Conditions that rule a roof out
- Wet, frosty, icy or dew-covered surfaces; moss, algae or loose granules.
- Wind strong enough to move a bundle or a sheet of plywood.
- Heat that softens shingles enough to scuff and slide.
- Working alone, or without someone on the ground who can call for help.
- A sagging or spongy deck.
DIY or professional?
Roofing a walkable single-storey roof is within reach of a capable homeowner with help, fall protection and patience; it takes three to four times a professional crew’s hours. The DIY vs pro calculator sets the cash saving against your time, and the roofing time calculator gives the professional hours to multiply. For steep, high or complex roofs, and for anyone unsure about the setup above, the honest answer is to hire it out; a roofer’s quote includes the equipment, the insurance and the experience. If a roof has a problem that needs looking at closely, a paid inspection costs far less than a fall. Repair or replace covers what to ask the inspector.