How are skyscraper windows cleaned?

The machine on the roof

That crane is a building maintenance unit, or BMU: a davit or trolley arm that rides a track around the roof and lowers a cradle holding one or two people and their water. Guide buttons in the facade stop the platform swinging off the glass on the way down.

On a supertall the BMU is designed in from the start, because it is a structural load: heavy, moving, hanging weight off the roof edge, so the slab and track must resist the overturning moment when the arm is out. Retrofitting one means finding structure to anchor it to, which is why older towers are more often cleaned from ropes.

The Burj Khalifa shows the full version. Its 828 m and 163 floors carry about 23,000 glass panels, worked by roughly eighteen machines and crews of around thirty-six, the highest davits above 740 m where the tower narrows past what a cradle can follow. A full pass takes about three months, worked in stages down the building, then starts again.

Ropes, cradles and bosun's chairs

There are two other ways down. A suspended scaffold is a powered platform hung on wire ropes from davits at the top, the long cradle seen on buildings under renovation. Rope access is the other: a descent on a working line from a certified anchor, sitting on a bosun's chair, a small seat board slung from the rope.

Rope access exists because glass is not flat. A tower with sloping facets or a tapering crown has places no cradle can sit square against, and the Shard in London is the case: eight panes angled inward so none meets the vertical. Those are worked by abseiling crews trained under the Industrial Rope Access Trade Association scheme, which certifies technicians at three levels on logged hours. The job title is window cleaner or facade technician; the rope qualification sits on top.

The water matters more than the tools. Tap water spots the glass, because its minerals stay behind as it dries, so high-rise work runs water through deionizing resin or reverse osmosis until the dissolved solids are near zero and it dries clear. Above the reach of a fed pole the squeegee still wins: a rubber blade pulled across wet glass by someone who can see the streak clears it in one pass.

The risk, and the rules around it

Falls are the hazard that matters; everything else on a facade is ordinary by comparison. The United States rules are specific. Every component of a rope descent system must hold a rated load of 5,000 pounds. The technician wears a harness on a fall arrest system independent of the line being descended, so the working rope is never the only thing holding anyone. Anchorages are certified by the owner in writing and the rig inspected every shift. Rope descent is barred above 300 feet unless another method would be infeasible or more dangerous, much of why supertalls have BMUs. Hazardous weather forbids it outright, and wind limits pull a cradle before conditions get dramatic, because a suspended platform in gusts becomes a pendulum next to glass. Crews close the sidewalk below with an exclusion zone.

A fatal fall in the trade is rare enough that individual accidents make national news. The consequence of a failure is severe, which is why the redundancy is mandatory, the same principle behinda tower's other safety systems: assume the single component fails and put a second behind it.

What the job pays

No United States government figure covers high-rise window cleaners on their own. Federal wage data files the work under janitors and building cleaners, whose median was $36,840 a year in May 2025, a category that mixes office and storefront cleaning in with facade work and so understates the height trade.

Trade and union figures put high-rise crews roughly between $40,000 and $80,000 a year, the spread driven by city and by how much of the work is at height. The floor is non-union work in a cheap market; the top is union facade work in an expensive one, where the New York local representing about 600 window cleaners puts members above $26 an hour with benefits, more than $54,000 before overtime. Read the upper end as experienced union crews in major markets, not a national average.

How often, and what the owner pays

Owners are quoted per pane or per drop, and access sets the price: a working BMU is cheap because the machine is already there. A commercial tower is washed two to four times a year, and the pass doubles as inspection, since the crew is the only person who gets within arm's reach of every gasket and fixing onthe curtain wall.

The robots

Machines are being tried and one has stuck. Ozmo, built by Skyline Robotics on an industrial KUKA arm with lidar and computer vision to read the facade, went into full-time service in August 2024 on a 45-story building at 1133 Avenue of the Americas in New York, after beta runs there and in Tel Aviv.

The limits are the honest part. It rides a conventional suspended platform, so it needs the rigging a crew needs, and it works flat, repetitive curtain wall; facets, setbacks and crowns are still hand work. Skyline's own argument for it is a shortage of people willing to do the job. Everything in the supertall category is still cleaned by people.