Wind on a Ladder and the Sheet You Carry Up It

Why this matters

Wind alone rarely takes anyone off an extension ladder on a day a crew would choose to work. What pulls people off is what they are holding. A sheet of plywood carried broadside up a ladder is a sail with a person attached to the mast, and a gust that would barely be noticed on the ground turns into a sideways shove at the one moment the person has one hand on the rail and their weight on one foot.

There is no wind rating on a ladder to tell you when to stop. That is the reason this card exists: the limit has to come from the load and the setup, and a shop has to set it itself. The ladder setup and tie-off is owned by 'How to Set and Tie Off an Extension Ladder So It Cannot Move'; how to read sustained wind against gusts is owned by Sustained Wind Versus Gusts and Which One a Limit Means.

Why a ladder has no wind rating

A ladder's duty rating, under the ANSI A14 standards ladders are built to, is a vertical load: the combined weight of the person, their clothing, tools and materials the ladder will carry. It says nothing about side load, because a ladder's failure in wind is not the ladder breaking. It is the person losing balance, or the ladder base kicking out or the top sliding sideways off its support.

So the questions are about the person and the setup, not the ladder:

• How much sideways force will the load put through the person's hands and body?
• Does the person have a free hand on the ladder while that force arrives?
• Is the ladder tied at the top and secured at the feet, so that a sideways shove from the climber does not move it?

Federal rules put the load question plainly. In construction work, 29 CFR 1926.1053 bars a worker from carrying any object or load on a ladder that could cause them to lose balance and fall, and requires a hand on the ladder when climbing; the general industry ladder rule at 29 CFR 1910.23 carries the same prohibition on balance-threatening loads. A sheet in wind is that load.

The force on a sheet, worked out

Wind force on a flat object facing the wind depends on its area, the square of the wind speed, and its shape. For standard air near sea level, the dynamic pressure of the wind in pounds per square foot is about 0.00256 times the wind speed in mph, squared. A flat plate square to the wind takes a force of roughly 1.2 times that pressure times its area; the 1.2 is an approximate drag coefficient for a flat plate broadside to the flow, and it varies a little with the plate's proportions.

Take a 4 by 8 foot sheet, 32 square feet, held broadside.

• At 10 mph: 0.00256 times 100 is 0.256 lb per square foot. Times 32 square feet is 8.2 lb, times 1.2 is about 10 lb.
• At 22 mph: 0.00256 times 484 is 1.24 lb per square foot. Times 32 is 39.6 lb, times 1.2 is about 48 lb.

Check it the other way: 22 mph is 2.2 times 10 mph, and 2.2 squared is 4.84. Ten pounds times 4.84 is 48 pounds. The two routes agree.

A half-inch sheet weighs something on the order of 40 to 50 pounds, depending on the panel. So at 22 mph the gust pushes sideways on the sheet with roughly its own weight. The person is already holding the weight vertically, which is hard enough on a ladder; now an equal force arrives sideways, without warning, and it arrives through a sheet whose far edge is four or eight feet from their hand, so it twists as well as pushes.

   gust 22 mph  -->  -->  -->

                 +-----------+
                 |           |
   about 48 lb   |  4 x 8    |   sheet held broadside,
   sideways  --> |  sheet    |   32 sq ft of sail
                 |           |
                 +-----------+
                       o  <- climber: one hand on
                      /|     the sheet, one on
                       H     the rail
                       H
                       H  <- ladder rail; the push
                       H     goes through the climber
                      / \    into the top and feet
                   ---------  ground

The climber and the ladder catch wind too

Without a sheet, the load is small. A person on a ladder presents something like 7 square feet to the wind, and a body is a blunter shape than a plate, with a coefficient near 1. At 22 mph that is about 1.24 times 7, or roughly 9 lb. The 4 by 8 sheet at the same gust was 48 lb, so the sheet multiplies the sideways push on the climber about five times. That ratio is the whole argument of this card in one number: the wind was never the problem, the area in the hands was.

The ladder itself has little area, but it fails in two wind-related ways that have nothing to do with the climber's hands:

• An unattended ladder blows over. A tall extension ladder standing against a gutter with nobody on it can be walked sideways and dropped by gusts, onto a car, a window or a person below. Tie it at the top whenever it stands, or lower it when nobody is using it on a gusty day.
• The top slides along its support. A ladder resting on a smooth gutter or a siding face has little to stop the top moving sideways when the climber is shoved. A top tie, or a standoff that bears on the wall rather than the gutter, is what holds it; that setup is in the tie-off card.

Which loads turn a person into a sail

The arithmetic carries to anything with area. The ones that come up most:

• Sheet goods. Plywood, OSB, drywall carried outside, foam board. Foam board is the trap: it weighs almost nothing, so the climber is not braced for load, and its area is the same as a plywood sheet's.
• Roof and wall panels. Metal roofing and siding panels are long and light. A 12-foot panel caught at one end acts as a lever, and its edges cut.
• Solar modules. A typical module is somewhere around 18 to 22 square feet. At the same 22 mph gust, 20 square feet takes about 30 lb sideways, by the same formula. Modules are also fragile and expensive to drop, which makes people grip harder and hold on longer than they should.
• Long gutter runs. A 20-foot gutter section has a small face but a long length. The problem is less push than rotation: a gust at one end swings the far end, and the climber is holding the pivot.
• Tarps and sheeting. Any fabric partially unfolded at height is the largest sail on site.

Worked example: two sheets up a one-story roof

A handyman crew is replacing two rotted sheets of roof sheathing on a one-story house with a 4 in 12 roof. The work is near the eave on the west slope. The forecast is 10 mph sustained, gusting to 22, from the west, which means the gusts hit the west elevation, the side the ladder is set on, square on.

The plan as first written. Set the extension ladder at the west eave, tie it off at the top, carry each new sheet up the ladder, slide it onto the roof, climb up after it.

What the numbers say. Each sheet takes about 10 lb sideways in the steady wind, which a braced person can handle, and about 48 lb in a gust, roughly its own weight, arriving on a climber with one hand on the rail. The crew has no wind limit for ladders written down. The lead sets one for the job: no sheet goods carried up the ladder broadside on a day forecast to gust over 15 mph. At 15 mph the same sheet takes about 22 lb sideways (0.00256 times 225 is 0.576, times 32 is 18.4, times 1.2 is 22.1), a little under half the 48 lb at 22 mph. There is no published figure for how much sideways force a climber can resist, so the 15 mph line is a shop judgment, not a derived limit. Set yours, and set it low.

The plan as changed.

1. The ladder moves to the east side, the lee of the house. The lee is not calm, wind swirls over a roof ridge and down the far side, but the steady push on that face is lower and the gusts arrive less squarely.
2. Nobody carries a sheet on the ladder. One person goes up first with nothing in hand and ties into whatever fall protection the roof work calls for. The second stays on the ground.
3. The sheets go up by hand line, tied through a corner and raised edge-first, so the sheet presents its thin edge to the wind rather than its 32-square-foot face. A tag line on the lower corner, held by the ground person, keeps it from spinning.
4. On the roof, each sheet is laid flat and immediately weighted or tacked down. A loose sheet on a roof in a gust can lift and slide, and the eave is where it will go.

The job takes perhaps fifteen minutes longer. The sideways load on anyone's body falls from about 48 lb to the effort of hauling a rope.

If the hand line is not possible. If there is nowhere to rig a line, the alternatives are a ladder-mounted material hoist, carrying the sheets up through the house to an access point if one exists, or rescheduling to a calmer day. Cutting the sheet into smaller pieces changes the repair, so it is a decision about the roof, not about the wind.

What changes the answer

• Gusts arrive from the side, not only head-on. A sheet carried edge-on to a forecast wind direction becomes broadside the moment the wind shifts, and it shifts most around buildings. Plan for the face, not the edge.
• A second person on the ladder does not help. Two people on one extension ladder is outside its use, and the second person is not in a position to brace the first.
• Height multiplies the consequence, not the force. The force on the sheet is about the same at 8 feet and 20 feet in the same wind, but the fall is not, and the wind at the second-story eave is usually stronger than at the first.
• Roof edge work has its own fall rules. Once the crew is on the roof, fall protection is governed by the rules for that work (in construction, 29 CFR 1926.501, with its 6-foot trigger); the ladder card does not replace it.

References

• 29 CFR 1926.1053, Ladders (construction), and 29 CFR 1910.23, Ladders (general industry)
• ANSI A14 ladder standards (duty ratings as vertical load capacity)
• See related: How to Set and Tie Off an Extension Ladder So It Cannot Move
• See related: Sustained Wind Versus Gusts and Which One a Limit Means; The Wind Hold for Ladders, Roofs and Spraying SOP
• See related: The Roof Panel That Caught a Gust at the Eave