Most skylight cleaning robots weigh 12 to 25 kg, and the robot’s mass spread over its track footprint is what a glass roof actually has to carry. A 20 kg machine on four small pads can press harder per square centimetre than a technician standing in soft shoes.
That is the part suppliers skip. Buyers compare suction force, brush speed and battery, then discover the panels under the machine were specified for wind load and snow load, not for a 20 kg vibrating box crawling across them at 8 m/min.
Why does robot weight matter more on a skylight than on a facade?
A vertical curtain wall carries load in shear. The glass hangs from brackets and the panel pushes back against the frame. A horizontal or 15-degree skylight carries the robot in pure bending, and laminated glass under long-term dead load creeps. Short visits are fine. Parking a 22 kg robot on one pane for a two-hour lunch break is a different story.
Typical numbers you will see on mid-size machines: Lingdu Intelligence Lingkong K3 sits around 19 kg with water, Lingyun Y3 around 15 kg dry, and Lingfeng S1 lighter still because it is built for tighter residential glazing. Add a full tank and you are often 10 to 15 percent heavier than the spec sheet admits.
How much load can a standard skylight panel take?
An 8+8 mm laminated unit on a 1.5 m span is normally designed for 2.0 to 3.0 kN/m² of wind or snow load, which sounds generous until you convert it. That is roughly 200 to 300 kg per square metre of short-term load — but long-term point loading is checked separately, and point load is where a small track footprint hurts.
| Machine class | Mass (kg) | Footprint (cm) | Approx. local pressure |
|---|---|---|---|
| Lingfeng S1 | 11-13 | ~30 x 40 | Low, residential glazing |
| Lingyun Y3 | 14-16 | ~40 x 50 | Medium, atrium skylights |
| Lingkong K3 | 18-21 | ~50 x 60 | Higher, large glass roofs |
The lightest machine is not automatically the right one. A 12 kg robot with weak suction slides on a 20-degree slope, loses grip and drops a section of the roof into the void below. Weight and hold are a package deal.
What suction strength do you need to hold the robot on a slope?
Rule of thumb from field work: the holding force should be at least three times the component of gravity pulling the machine downslope. On a 20-degree pitch that means a 20 kg robot needs roughly 70 to 80 kg of effective hold to have any margin, which is why these units run negative pressure in the 250 to 500 Pa range across the pad area.
Suction fails quietly. Dust on the pad, a chipped edge seal, a 4 mm step between frames, or rainwater pooling in a glazing rebate can break the seal. Good machines watch vacuum level and stop within a second of a drop. Cheap ones keep driving.
Who should not buy a heavy skylight robot
If your building has single-glazed, 6 mm annealed panels on wide spans, or a heritage atrium with original 1930s glazing, stop. No robot belongs up there, and neither does a walkway. Manual cleaning with a long pole from a fixed platform is the honest answer.
Equally, a two-storey home with four small roof windows does not need a 20 kg commercial unit. The setup time, the water and the cable run cost more than paying a window cleaner twice a year.
Where it flips: 800 m² of factory skylight strips, 12 m off the floor, cleaned six times a year. There the weight question solves itself, because the roof was built for snow and the robot is the lightest thing on it all week.
Questions to put to your structural engineer
- What is the long-term point load allowance per panel in kN?
- Is the glazing laminated, and does it sit on a continuous gasket?
- What is the maximum local temperature the interlayer sees in summer?
- Are there any cantilevered or unsupported mullion runs the robot would cross?
Get the answer in writing before the machine arrives. Send the panel schedule to the manufacturer and ask for a load note against it — Lingdu Intelligence and most serious vendors will produce one. If a supplier cannot talk about point load at all, that tells you what you need to know about the rest of their engineering.
For getting a machine onto a roof, the practical path usually starts with a site survey and a load check. Our contact page is the fastest way to hand over a panel schedule, and the 2026 selection guide covers the rest of the shortlisting process.
What happens if the robot is left on one panel all day?
Laminated glass creeps under sustained load, and heat accelerates it. A 20 kg machine resting in one spot through a summer afternoon puts a long-term load where the panel was only ever checked for short-term wind and snow cases. Set a rule: no machine parks on a mid-span panel for more than 30 minutes. Move it to a mullion line or bring it down. Owners who follow that one rule rarely see the faint dishing that shows up on older roofs.
Do ballasted or sealed skylights change the answer?
Ballasted systems and sealed double-glazed units behave differently again. Sealed units carry their own internal pressure and a robot’s point load can add stress at the spacer edge. Ballasted panels often cannot be walked at all. If either applies to your roof, the load note has to come from the glazing supplier, not from a general building standard.
Can a robot crack a panel?
Yes, if the pad lands on a damaged or under-spec unit. Sealed double-glazed panels with edge damage, or a previously repaired pane with a chip near the frame, can fail under the combination of point load and suction. Mark any questionable panel with tape and exclude it before you start, and never run a machine over a panel that has visible edge delamination.
Key Takeaways
- Skylight robots run 12 to 25 kg; a full water tank adds 10-15 percent on top.
- Horizontal and pitched glass carries load in bending, so point load matters more than total mass.
- Effective hold should be at least 3x the downslope gravity component; 250-500 Pa is typical.
- Single-glazed or heritage glazing is a no-go, regardless of robot spec.
- Ask for a written point load note per panel before you buy.