A conservatory roof is not a big window. It faces the sky rather than the horizon, so it collects what falls rather than what blows past, it drains into gutters nobody looks at, and a good share of what makes it look dirty is not dirt at all. That is why it is quoted separately from a window round and usually booked separately. Know what yours is made of before you get anyone out, because glass and polycarbonate have different methods and different limits.
Glass or polycarbonate, and why it changes the method
Glass roofs are toughened or laminated and behave much like the rest of your glazing: brush, detergent, and they come up properly clean. Newer installations often carry a self-cleaning coating, which wants plain water and a soft head, because polishes and strong chemicals damage it and it cannot be reapplied.
Polycarbonate is soft. A scouring pad, a stiff brush or grit trapped under a cloth leaves a permanent haze, and there is no polishing it out. It is flooded and rinsed rather than scrubbed.
It also has a UV-protective face meant to point at the sky. Once that has weathered, the sheet goes cloudy and slightly yellow and no cleaning reverses it, so a roof can be entirely clean and still look tired. Anyone quoting should ask which material you have. If they do not ask, they are pricing the wrong job.
Growth sealed inside the flutes
This is what people most expect cleaning to fix, and the one thing it genuinely cannot.
Twin-wall and triple-wall polycarbonate sheets are hollow, divided into narrow channels called flutes running from the ridge to the gutter. The ends are sealed when the roof is built, and after a decade or two most of those seals have failed, letting water and spores inside to grow there. From underneath you see dark vertical stripes, evenly spaced, following the line of the sheet. They read as filth on the panel. They are inside it, between two walls of plastic, and nothing applied to either face reaches them.
What can honestly be done: clean both faces, which removes the surface growth sitting on top of the internal staining and often making it look worse than it is; reseal failed end caps and breather tape so less water gets in from here on; and say plainly what will still be visible afterwards. If someone offers to flush the flutes out, ask how the water comes back out. Replacing the affected panels is the only real fix, and that is a glazing job.
Algae and lichen on the shaded side
Roof glazing greens up unevenly. The north-facing slope, the side under a tree, and the strips nearest the ridge and the gutter go first, because those stay damp longest. Algae is a green film that comes off with detergent and dwell time. Lichen is the crusty grey growth fixed to seals, glazing bar tops and gutter edges, and it needs softening and lifting rather than scraping, which takes the finish off aluminium and gouges plastic.
The pattern matters more than the growth. If one slope greens back within weeks, something is keeping it wet: an overhanging branch, a blocked gutter above it, or a downpipe discharging across the glass. Cleaning that panel four times a year without touching the cause is money spent on a symptom.
Nobody should walk on a conservatory roof
Conservatory roofs are not designed to carry a person, and polycarbonate becomes brittle with age, so a roof that looks solid can fail underfoot without warning. The work is done from the ground with a pole and a soft brush head, or from a properly footed position at the eaves for the gutter line, never by standing on glazing or glazing bars. Where a pole cannot reach, the answer is a tower or a platform, which changes the price. It also means the work happens in your garden, so a locked side gate or a border planted tight to the frame changes how the job runs.
Gutters, box gutters and the junction with the house
The gutter usually needs the work more than the glass does. A conservatory sheds a large area of water into a small gutter set low down, and once it silts up, water sits along the bottom edge of the glazing, exactly where the seals are.
The box gutter is the important one. On a lean-to this is the channel where the roof meets the house wall, tucked under the flashing and out of sight. It fills with moss, backs water up behind the flashing, and produces damp indoors that gets blamed on the roof for years. If your conservatory has one, it should be cleared at the same visit.
Late autumn, once nearby trees are bare, is the sensible slot for the whole job. Doing it in spring means clearing a gutter that refills in October.
Inside: condensation, ventilation and the drainage channels
The interior of roof glazing is dusty rather than dirty. Sheet joints drop fine debris, cobwebs collect in the frame corners, and dead flies gather in the glazing bar channels and along the bottom of every frame. Those channels drain condensation out through weep holes in the outer face, and when they silt up the water goes onto your floor instead. Clearing them takes minutes and solves a puddle people have lived with for years.
Interior roof glass also streaks badly in the heat. A glazed room can be well over thirty degrees by mid-morning in July, and solution dries before a squeegee reaches it, so a cool morning in spring or autumn is the honest slot.
Condensation itself is ventilation, not cleaning. Roof vents that no longer open, trickle vents felted solid with road dust, and a room shut up all winter will produce a green bloom in the glazing bar channels however often the glass is done. The vent mesh lifts out in one grey mat. Not strictly glass work, and worth doing anyway.
Frames, seals and glazing bars
Aluminium glazing bars hold growth along their edges and oxidise to a chalky finish that returns after cleaning. UPVC frames yellow under UV and respond to a UPVC-specific cleaner, tested in a corner first. Perished gaskets are worth flagging rather than working on: hard, shrunken rubber lets water past and cleaning around it does nothing. Same with a misted side panel, where the fogging is between the panes.
How often
| Situation | Roof glazing |
|---|---|
| Open aspect, nothing overhanging | Once or twice a year |
| Trees or hedging nearby | Twice a year, one in late autumn |
| North-facing slope, persistent algae | Two to three times a year |
| Interior roof glazing | Once or twice a year |
| Gutters and box gutter | Annually in autumn, more with trees |
Conservatories want the outside doing more often than the inside, and both less often than the windows on the house.
What makes a quote vary
Conservatory roofs are quoted after somebody has seen the roof rather than priced from a list. What moves the figure:
- Material and age. Brittle old polycarbonate is worked differently from toughened glass
- Shape. A lean-to is straightforward. A Victorian roof with facets, a ridge and finials is not
- Reach. Pole from the ground, or a tower because of a slope or planting in the way
- Condition. A roof done annually takes a fraction of the time a neglected one takes
- Whether gutters are included, and whether the inside is wanted as well as the outside
Across the trade, conservatory roof cleaning is commonly quoted from around £30 for a small lean-to to well over £100 for a large or long-neglected roof, with gutter clearance often a separate line. That is a market range rather than anybody's quote.
Frequently asked questions
Can you get the green stripes out of my polycarbonate roof? Not if they are inside the sheet. Growth in the flutes sits between two walls of plastic and cannot be reached from either face. The surfaces get cleaned, failed ends resealed, and the striping stays until the panels are replaced.
Is the conservatory roof included in a window clean? Normally no. It is quoted and booked separately, because it takes longer than the rest of the house put together and needs a different method.
Can I clean it myself? The lower edge from the ground with a soft brush on a pole, yes. Not from a ladder leaned against the frame, and never by getting onto the roof. Conservatory glazing will not hold your weight.
Does a pressure washer work on a conservatory roof? No. Pressure drives water past seals and into the flutes of polycarbonate, and it lifts capping and gaskets. Low pressure, a soft head and thorough rinsing is the method.
Will cleaning fix my condensation? No. Clearing the trickle vents, roof vents and drainage channels helps, but the underlying fix is airflow and heating.
