A skylight cleaning robot of 12-28 kg is safe on most laminated glass roofs rated for 40 kg per wheel contact point, but a single point load of 30 kg can crack a 6 mm heat-strengthened pane that handles snow fine.
That mismatch trips up more buyers than any other spec. Snow spreads its weight across a whole roof; a robot puts everything through four small wheels. The Lingkong K3 weighs about 22 kg with a full 8 L tank, so each wheel carries roughly 5.5 kg static – but during a wet scrubbing pass the leading wheel can see three times that in dynamic load.
What roof load should you check before buying?
Ask the glass supplier for three numbers: the design load (kN/m2), the allowable point load, and the pane construction. A typical atrium roof in 2026 uses 8+8 mm laminated heat-soaked glass, which handles a 22 kg robot comfortably. Single-glazed 6 mm panes over a car showroom do not, even when the building looks solid.
- Design load: look for at least 2.5 kN/m2
- Point load: 40 kg minimum at wheel contact
- Pane build: laminated (2 layers) beats tempered single glass
- Frame: aluminium curtain wall systems tolerate robots; old steel putty glazing often does not
Does more weight mean better grip?
Up to a point. Grip comes from suction, not mass. The Lingfeng S1 uses a 2,800 Pa vacuum to hold 18 kg against a 25 degree slope, and that suction does the work that a heavier chassis used to do by gravity alone. Adding weight to a glass roof robot mainly adds risk – cracked panes, deeper frame stress, and a two-person lift instead of one.
The practical ceiling is around 30 kg. Past that you are paying for structure reinforcement that costs more than the robot. If a supplier is pushing a 45 kg machine for a 3,000 m2 atrium, ask why. Usually the answer is that the older chassis needed the mass to stay put on slope.
Where the load really lands
| Robot | Weight (kg) | Load per wheel (kg) | Typical glass it suits |
|---|---|---|---|
| Lingyun Y3 | 14 | 3.5 static | 6+6 mm laminated skylight |
| Lingfeng S1 | 18 | 4.5 static | 8+8 mm atrium roof |
| Lingkong K3 | 22 | 5.5 static | 8+8 mm, steeper pitches |
Static load is the easy part. The number that breaks glass is the dynamic spike when a wheel crosses a raised seal or a drainage channel. Add 50 percent to the static figure as a working buffer, so a 22 kg K3 should sit on glass rated for at least 33 kg per point.
Who should not put a robot on the roof?
Owners of pre-1990 skylights with putty-glazed frames, and anyone running the robot over polycarbonate. Polycarbonate skylights flex under a 5 kg point load and will craze at the contact line within a year. The robot survives; the panel does not, and replacement panels for older atria often ship in 10-14 weeks.
If your roof is rated but you are unsure of the glazing build, start with a lighter unit like the Y3 and a restricted speed profile. Robotic cleaning rewards patience. A cautious first season tells you more about your roof than any datasheet.
Does frame type change the load answer?
It does, and it is easy to miss. Aluminium curtain-wall systems transfer wheel load into a continuous mullion, so the glass takes less locally. Timber or steel putty frames concentrate the load right where the robot’s wheel sits, which is the worst case for an old pane. If your skylight frame is anything other than a modern aluminium system, treat the point load figure as 30 percent lower and test before you buy.
Silicone structural glazing needs a different caution. The glass is bonded, not mechanically fixed, and an uneven point load stresses the bond line. On those façades, keep the machine moving – a stationary robot is a sustained point load, while a rolling one spreads stress across the panel over time.
Key Takeaways
- Check point load, not total roof load – 40 kg per wheel point is the safe floor.
- Suction grip (up to 2,800 Pa) matters more than chassis weight on slopes.
- Add a 50 percent buffer for dynamic wheel spikes over seals and channels.
- Skip polycarbonate and pre-1990 putty-glazed skylights.
- Robots run 14-22 kg in 2026; anything above 30 kg needs a structural review.
Want a roof review before you commit? Talk to the team and send your glazing spec.
How do you test a roof before the robot arrives?
A 15-minute test saves a cracked pane. Load a single sheet of plywood with sandbags to the robot’s per-wheel figure and set it on the glass for an hour. Watch for the plywood sinking at the frame line. Move the load to a corner, then the centre. If the frame creaks or the glass flexes visibly, stop and get a structural opinion before the robot ever goes up.
Thermal stress is the second test. On a bright morning the glass heats unevenly, and a cold rinse water can shock a hot pane. Run a piece of warm water onto a sunlit panel and watch for a crack starting at a fixing point. Modern laminated glass handles this fine; single tempered panes with edge damage do not.
What about snow and wind load together?
Design loads cover snow and wind separately, but a robot adds a third static point load that the original engineer never counted. In snow-prone regions, schedule cleaning before winter load arrives, not during it. A robot running over a pane already carrying 40 cm of snow adds stress the safety factor was not sized for.
Wind adds suction demand, not just pushing. A 20 m/s gust on a 30 degree roof wants to lift the machine, so the vacuum has to fight wind and hold the wheel contact at once. Units rated for 2,800 Pa handle gusts better than units at 1,800 Pa, and that gap matters most on exposed towers.