Run skylight cleaning robots at night when the building is empty and the glass is cool, and during the day when you need full visibility and a spotter. For hot roofs above 40 C, night work is the safer default in 2026.
Scheduling sounds like an afterthought. On skylights it changes both the cleaning result and the safety case. Heat, glare, public access and supervisor availability all move with the clock.
Why does glass temperature matter for robot cleaning?
Rinse water evaporates before it can carry dirt away on hot glass. A skylight in direct summer sun can sit at 50-60 C surface temperature. Cleaning it with ambient-temperature water means the squeegee leaves mineral residue behind, and the harder the water, the worse the marks.
Early morning is the sweet spot for most roofs. Glass has cooled overnight, water stays liquid long enough to flush dirt, and there is usable light. Night work adds artificial lighting and a higher supervision demand. If you must work hot, pre-cool the pane with a light wetting pass before the cleaning pass.
What are the supervision rules for night work?
- Two people minimum: one operating, one watching the tether and edge.
- Portable lighting directed at the glass, not the operator’s eyes.
- A radio check every 15 minutes if the roof is out of sight.
- A retrieval plan for a stalled machine written down, not improvised.
Solo night work on a roof is where most incidents happen. Fatigue plus poor light plus a machine that can slip is a bad combination, and no throughput figure justifies it.
How do you pick a window per building type?
| Building | Best window | Reason |
|---|---|---|
| Retail mall atrium | 01:00-05:00 | Empty floor, no public risk |
| Airport terminal | 23:00-04:00 | Reduced footfall, cool glass |
| Factory monitor roof | 06:00-09:00 | Shift gaps, cool start |
| Office podium | Weekend day | Visibility, no tenant disruption |
Airports complicate this because roofs sit above zones that never fully close. Plan the lanes around active gates and keep noise under the local limit; a robot is quieter than a pressure washer but not silent.
Who should clean during the day instead?
Buildings with no safe night access, no lighting infrastructure, or a first-time operator learning the machine should run in daylight. Learning a new robot on a dark roof is a poor idea. Once the crew knows the lanes and the edge behaviour, night shifts become viable. See how runtime shapes a night plan in our battery guide.
Key Takeaways
- Hot glass above 40 C rejects rinse water and leaves residue; prefer cool hours.
- Early morning balances cool glass with usable natural light.
- Night work needs two people, directed lighting and a written retrieval plan.
- Malls and airports fit 23:00-05:00 windows; factories suit early shifts.
- Train crews in daylight before starting night shifts.
How does the shift pattern affect crew cost?
Night rates are higher in most markets, often 1.25 to 1.5 times day rates once premiums and transport are counted. That extra cost has to come back through better output or fewer disruptions. On a cool night roof, a machine runs nearer its rated speed and the crew is not fighting heat, so the throughput gain can offset part of the premium. It rarely offsets all of it.
Do the maths per building. A mall that can only be cleaned after midnight will pay the premium anyway, because there is no alternative. An office podium with a weekend window can use cheaper day labour and lose nothing.
What are the safety traps of night work?
- Depth perception drops; roof edges look closer than they are.
- Tether and harness checks get rushed when everyone is tired.
- A machine fault is harder to diagnose in the dark.
- Emergency access to the roof takes longer at night.
The trap that catches people is fatigue on the second or third consecutive night. One night is manageable. Three in a row is where incidents cluster. Rotate the operator or build a rest day into the schedule.
Can you split a roof between day and night?
Yes, and it is often the best answer. Clean the zones over sensitive rooms at night and the rest during the day. On a mixed mall roof, the atrium over the empty floor can be done at night while the back-of-house skylights wait for daylight. This keeps cost down without exposing anyone to unnecessary night work.
What is the one mistake operators make?
Treating the night shift as a way to work unsupervised. The temptation is to set the machine going and go home. That is how a stalled robot sits on a roof overnight, and how a small fault becomes a major repair. Night work is not less supervision; on a dark roof it is more.
Schedule the same two-person rule regardless of the clock. The savings from dropping a spotter are outweighed the first time a machine slips near an edge.
How do you brief a night crew?
Hold a short briefing before dark, not on the roof. Walk the lanes, point out the edge and the tether points, and name who does what if the machine acts up. A five-minute huddle in daylight is worth more than an hour of improvisation under floodlights, and it sets the two-person rule before anyone is tired.
What about residents near a night window?
Give advance notice and a contact number. Most objections come from surprise, not from the actual sound. A short note delivered two days ahead, naming the night and the duration, turns a complaint into a non-event. It costs nothing and it is the single most effective noise control available.