For a glass roof, a roof cleaning robot needs a slope rating above your maximum pitch, suction headroom for condensation, a documented anchor point and a frame-crossing or edge-stop behaviour that matches your mullion layout. Consumer units rated to 15 degrees fail on 25 degree roofs.
Skylight cleaning is the use case these machines were not originally designed for, and it shows in the specifications. A machine tuned for vertical glass has gravity working on its side. On a pitched roof light, gravity is the enemy.
What slope rating do you need?
Match to your worst month, not your average. Measure the actual pitch with an inclinometer on the glass, not from the architectural drawings. Then add 5 degrees of margin. If the roof is 22 degrees, buy for 27.
Skylights over atriums are often steeper than owners assume. A common profile is 25 to 35 degrees. Most consumer robots top out at 15 to 20. That is not a minor gap, it is outside the operating envelope.
If you need crossing too, our Lingfeng S1 review covers a unit with both a higher slope rating and frame-crossing behaviour, which is the combination glass roofs actually need.
How much suction headroom does a skylight need?
Add 25 to 40 percent over the vertical-glass requirement for each 10 degrees of pitch, and another margin for wet glass. Morning condensation is the killer: it does not reduce suction, it reduces friction, and you get a robot that holds but does not move.
Watch for the case where suction is fine and the drive wheels spin. The fix is usually a dry first pass with low water, not more suction. Increasing suction on a wet pitched panel often just presses the robot harder onto a lubricated surface.
Where does the anchor go?
To a structural member, rated at three times the robot’s weight including any dynamic swing. On a roof, the temptation is the parapet, and parapets are frequently non-structural capping over insulation. Get it confirmed by whoever signed the structural drawings.
Route the rope so it cannot cross the cleaning path. On a pitched glass roof this means anchoring uphill of the work zone and keeping the line off to one side. A robot that rides over its own tether lifts an edge and loses seal.
What roof lights are unsuitable for robots?
Domes and curved glazing, glass with embedded decorative frit above a few millimetres of relief, frameless structural glazing with no positive stop at the edge, and any skylight where the fall zone below is a public space and the safety case is undocumented. That last one is the one people argue about and the one that matters.
Also skip robots on old single-glazed roof lights with visible seal failure. The flex under suction load can crack a pane that was already compromised. A 6 mm pane with a 20-year-old seal is not the place to test suction ratings.
How often should a roof cleaning robot run?
Quarterly is the typical facility schedule, monthly on dusty sites or buildings near major roads. Rain does not reset the clock: rain leaves mineral spotting that needs a machine pass, and on pitched glass it deposits the dirt at the low edge.
Budget for pads and seals on that schedule. At quarterly use a set of pads lasts about a year; at monthly use, expect two to three sets and a seal replacement. Our skylight robot reviews note consumable intervals per model where we have the data.
How do you test a roof before committing?
Do a dry run on the steepest pane on a dry afternoon. Watch the wheels, not the suction reading. If the unit slips when the glass is dry, no setting will save it when the glass is wet. That test takes 15 minutes and settles most of the argument.
What should you not assume?
How do you handle multiple roof lights on one building?
Treat them as one zone with a shared anchor, not as separate jobs. Route the tether once and move the robot between panes. On a spaced arrangement, six roof lights of 2 square metres each is a 30-minute cycle plus repositioning, against six separate ladder setups that eat an afternoon.
Weather delay is the other factor people miss. Wind at roof level runs higher than at street level, often by 30 to 50 percent on a building with any height. A gusty day can stop work when the ground feels calm. Build slack into the schedule instead of promising a fixed date.
What does maintenance of the machine itself look like?
Wipe the seal after every run, check the pad for embedded grit, clear the sensor ports, and store the unit upright indoors. Once a season, inspect the tether for abrasion at the anchor end and check the blower intake. Ten minutes of checks a month is the difference between two years and five.
Consumables are the ongoing cost. Pads wear fastest on dusty sites, seals degrade faster in UV. A machine used quarterly on a shaded roof light may go three years on original parts; the same unit monthly on a sun-exposed roof will need a seal inside 18 months.
- Measure actual pitch and buy 5 degrees above it.
- Add 25 to 40 percent suction per 10 degrees of slope.
- Anchor to structure rated 3x robot weight, never a parapet cap.
- Domes, curved glass and frameless glazing are out of scope.
- Quarterly minimum schedule; rain does not count as cleaning.