The short answer
Clean a conservatory roof from the ground or from inside, using a soft brush on a long pole, lukewarm water and a little mild washing-up liquid. Never stand or kneel on it, because roof sheets and glass are not built to carry a person. Marley does not recommend jet washing roof coverings, and forced water can find its way behind the seals.
A conservatory roof looks easy to reach and is not. The safe routes stay on the ground, and the rest is a job for proper access.
Why you should never stand on it
Polycarbonate sheets, glass units and the thin glazing bars that hold them are designed to keep the weather out, not to take a person's weight. A sheet that looks solid can flex, crack or pop out of its bar the moment someone puts a knee on it. Moss and algae make the surface slippery as well, so even a roof that holds still can send you sliding towards the gutter.
What about laying a board across it?
A scaffold board spreads the load, but it does not make the surface safe. The board itself can skid on a wet, mossy sheet, and the bars underneath were never sized for it. The safe rule is simple, and it saves a trip to casualty. If the only way to reach a patch is to put your weight on the roof, that patch is not a DIY job.
Roofers use a roof ladder or a crawl board that bears on the bars, or they work from a tower or scaffold alongside. That is also why a cleaning visit can cost more than the area suggests: the access is often the larger part of the effort, and the safe set-up takes time before any washing starts.
Gentle ways to clean from the ground
Most conservatory roofs can be kept presentable without leaving the ground. Start by clearing leaves and twigs from the gutter and along the lower edge, because debris holds water against the seals and feeds moss.
What do you use on the sheets?
A soft-bristle brush or soft cloth on a telescopic pole, a bucket of lukewarm water and a small squeeze of washing-up liquid. Work from the top downwards, so dirty water runs over the part you have not cleaned yet, and rinse with a hose on a gentle setting. Pick a dull, cool day if you can, because sun dries soapy water into streaks on the sheets. Avoid stiff bristles and scouring pads, which scratch polycarbonate and glass and leave a surface that picks up dirt faster next time.
Can you clean it from inside?
Yes, with a long-handled squeegee and a step ladder set on firm, level ground. Inside is where you see algae sitting between the layers of twin-wall sheets. That growth cannot be reached with a brush, and it usually means the end seals have failed and the sheet needs a roofer's attention. A weekend of scrubbing will not shift it.
What to avoid putting on the roof
High-pressure water is the usual mistake. Marley, the roof tile maker, says jet washing is not recommended for its tiles and slates, as the blast scars the surface and cuts into its working life. A conservatory roof is more delicate than either of those, and the rubber seals and end caps take the worst of any rough treatment. Water driven at pressure can slip behind the rubber glazing seals and into the end caps, and a roof that was dry last week then starts to drip along one bar.
What about bleach and moss killers?
Leave bleach, solvents and abrasive powders in the cupboard. They can cloud a sheet and perish the seals. Biocidal moss killers are a different matter. HSE tells householders to stay away from biocides sold for professionals only, and the law expects every product to be used as its approval says. If the label says professional use only, it stays on the shelf.
Our answer on moss on a polycarbonate roof covers thick, stubborn growth and the sheets that have turned green on the inside.
When a roofer should do it
Pick up the phone when moss has built into a thick mat, when the roof sits above a first-floor window or a drop, or when you can see cracked sheets, lifting bars or green lines inside the sheets. Cleaning can hide a fault for a week, but it cannot repair one.
What does a roofer do differently?
We look at the whole roof before cleaning any of it. That means checking the bars, the seals, the gutter and the flashing, the lead strip at the join with the house wall. Then you get photographs of the actual roof, so the choice rests on the facts: a wash, or something more. If a repair makes sense, the written price covers it as one total.
Sometimes the survey tells a different story. An ageing roof may be worth replacing rather than cleaning, and our conservatory roofs page sets out the options. If water is already coming in, read why a conservatory roof leaks before you book anything, and ask for a look at the roof first.
More on keeping a conservatory roof clean
How often should a conservatory roof be cleaned?
There is no set interval. Trees overhead, a north-facing aspect and shade all speed up moss and algae. A look from the ground a couple of times a year tells you more than a calendar. Wash it when dirt or green growth shows, and clear the gutter as often as it collects leaves.
Is a power hose a good idea on polycarbonate?
It is best avoided, and Marley does not recommend jet washing roof coverings. A jet can scratch the sheet and force water past the glazing seals and end caps, leaving you with a leak that was not there before. A soft brush, lukewarm water and patience do the job without risking the seals, and anything that will not shift is a roofer's call.
The full picture: Conservatory roofs in Taunton ยท More short answers