Roofs and solar panels, without walking on them
Soft washing roofs and rinsing solar arrays by drone keeps boots off fragile surfaces and people off steep pitches. The service is coming; register now to be assessed first.
Moss, algae and why pressure washing is the wrong tool
On the West Coast, roofs grow things. The dark streaks on asphalt shingles are usually algae; the green cushions are moss, which holds water against the roof, lifts shingle edges and fills gutters. Lichen grips harder than either.
The asphalt roofing industry is clear on method. Its manufacturers' association advises against pressure washing shingles, because it strips the granules that protect the asphalt from sun, and recommends a dilute bleach solution applied with a sprayer, left to dwell, then rinsed with low-pressure water, with landscaping protected. That is a soft wash, and it is what a drone does well: even application over the whole roof from above, with no one walking on it.
What a drone cannot do is pull up thick moss mats. Where moss is heavy, hand removal from a safe position comes first, or the roof is treated and left for the growth to die back and weather off. Tile, slate and some metal roofs are easily cracked or dented underfoot, which is another reason to keep people off them.
Killing moss is regulated, cleaning a roof is not the same thing
Products sold to kill moss are pesticides. In Canada they carry a Pest Control Products registration number on the label and are regulated by Health Canada; in the United States they carry an EPA registration number. The label is the law for how the product may be used.
In 2026 Health Canada began allowing pesticide application by drone, but only for products already registered for aerial application. Most roof moss products are not. Provinces add their own rules: in British Columbia, applying many pesticides for hire requires a licence and certified applicators, and some municipalities restrict cosmetic pesticide use. In the US, dispensing a pesticide from a drone can bring in FAA Part 137 on top of Part 107; see drone rules in the United States.
Our plan for roof work is cleaning and rinsing. Any moss-control product is a separate decision made against its label and the local rules, and we will tell you which parts of the job that affects. See safety and environment for the aviation side.
Solar panels: clean gently, by the warranty
Dirty panels produce less. Pollen, bird droppings, tree sap, construction dust and road grime build up, especially along the lower edge of low-tilt arrays where rain leaves a line of silt. Rain helps on the coast but rarely finishes the job.
Panel makers publish cleaning instructions, and they are strict. Across the major manufacturers the common points are: use clean, low-mineral water such as deionized water; no high-pressure washers; soft brushes or sponges only; no abrasive cleaners, solvents, acids or strong alkalis; and clean in the cooler part of the day so cold water does not hit hot glass. Some state a maximum pressure. Cleaning outside those terms can void the panel warranty.
A drone rinse with pure water at low pressure fits those instructions well, and it keeps crews off roofs where walking between panels risks both the panels and the people. If output has dropped more than dirt explains, a thermal solar inspection first finds hot spots, cracked cells and failed connections that cleaning will not fix.
Roof and array cleaning methods
| Method | Works well for | Risks |
|---|---|---|
| Pressure washing | Concrete and hard surfaces | Granule loss on shingles, cracked tiles, water forced under laps, often outside solar warranties |
| Hand soft wash from the roof | Low-slope roofs with safe access | Fall exposure, foot damage to tiles and panels, fall protection set-up time |
| Hand work from a lift | Low buildings with room for a lift | Reach limits, landscape damage, set-up space |
| Drone soft wash and rinse | Steep, fragile or large roofs and roof-mounted arrays | No scrubbing, wind limits, drift that must be managed |
Where roof and solar cleaning fails
Granules in the gutter
Pressure washing makes a shingle roof look new for a season and shortens its life.
Solution burns the garden
Bleach-based solutions harm plants and lawns below the eaves if runoff is not managed.
Voided solar warranty
The wrong water, pressure or brush can give a manufacturer grounds to refuse a claim.
Gutters overflow after cleaning
Dead moss and debris wash into gutters and downspouts.
How roof and solar work will be planned
Identify the roof
Material, age, slope, known leaks and any warranty. A roof inspection is often worth doing in the same visit.
Identify the array
Panel make and model, mounting, inverter data if you have it, and the manufacturer's cleaning instructions.
Protect below
Plants, decks, cars and drains mapped and protected.
Test area
A small section cleaned and checked before the whole roof.
Clean and rinse
Solution at low pressure where needed, dwell, pure water rinse, gutters checked.
Questions
Can a drone remove moss from a roof?
A drone can apply a cleaning solution and rinse, which kills and loosens light growth. Thick moss mats still need hand removal. Products sold specifically to kill moss are regulated pesticides and are used only as their label allows.
Is it safe to pressure wash asphalt shingles?
The asphalt roofing manufacturers advise against it because it strips the protective granules. Their recommended method is a dilute bleach solution, dwell time and a low-pressure rinse.
Does cleaning solar panels void the warranty?
Cleaning does not, but the wrong method can. Manufacturers generally call for low-mineral water, low pressure, soft tools and no harsh chemicals. Check your panel's installation manual.
How often should solar panels be cleaned?
It depends on tilt, trees, birds, nearby roads or construction and rainfall. Manufacturer guidance ranges from yearly to every few years. Monitoring output over time tells you when soiling is costing you.
Can a drone clean solar panels on a commercial roof?
Yes, the method suits large rooftop arrays, and it avoids walking between rows. The site assessment checks access, water supply and electrical safety around the array.
When is the best time to clean a roof on Vancouver Island?
Dry spells with mild temperatures, so solutions do not dry too fast and rain does not wash them off. Late spring and early fall are common windows.
Do I need a licence to kill moss on a roof in BC?
Homeowners using retail products on their own property follow the label. Applying many pesticides for hire in British Columbia requires a provincial licence, and some municipalities restrict pesticide use. Check the provincial rules for the product.
Keep reading
Exterior cleaning by drone · ComingExterior cleaning by drone, launching soon →
InspectionEvery slope, without anyone on the roof →
InspectionFind the panels that stopped pulling their weight →
Exterior cleaning · Safety and environment · ComingSafe in the air, clean at the drain →
Exterior cleaning · Strata and property managers · ComingExterior cleaning your council can plan →
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An address and what you need is enough to start. We reply with the price, who will fly it and when.