Cleaning a conservatory roof safely
From the ground, with soft tools and no pressure washer. The roof will not take your weight and the plastic scratches.
You cannot stand on it
A conservatory roof is a fragile surface in the formal sense. Polycarbonate sheet carries almost no point load, glazing bars are not walkways, and even toughened glass units are not designed to be stood on. Falls through conservatory and rooflight glazing are a recognised cause of serious injury.
That is why the whole job is done from the ground with poles, or from a ladder set alongside and never resting on the roof. If something genuinely cannot be reached from either, the answer is a tower or a contractor rather than a careful step onto a glazing bar.
- No point load at all
- Not on the sheet, not on the bars. Both are glazing components rather than structure.
- Never rest a ladder on it
- The ladder goes alongside against the wall, or on a stand-off. Not on the roof or the frame.
- Poles first
- Almost all of it is reachable from the ground with a telescopic brush and a hose.
- Out of reach means a tower
- Not a careful step onto a bar. That is the decision that causes the accidents.
No pressure washer
A pressure washer does three things to a conservatory roof, all of which cost money. It drives water past the seals and into the roof, it lifts the capping and the gaskets on the glazing bars, and on polycarbonate it strips the UV coated surface layer.
That coating is what stops the sheet yellowing and going brittle. Once it has been blasted off, the sheet degrades in a few years rather than twenty. A soft brush and a hose does the job without any of that.
- It forces water past the seals
- Straight into the roof build up and often into the room. The leak appears later and looks unrelated.
- It lifts cappings and gaskets
- Once a capping has lifted it does not reseat, and the roof then leaks at that bar.
- It strips the UV layer
- On polycarbonate that coating is the sheet's whole lifespan. Removing it is not recoverable.
- Soft brush and hose instead
- Slower and it cleans just as well without any of the above.
Green algae inside polycarbonate
Multiwall polycarbonate is hollow, and the green staining people find most annoying is algae growing inside the flutes rather than on the surface. Washing the outside does nothing to it, which is why the roof still looks green after cleaning.
It gets in through unsealed or failed ends. The sheet ends should be sealed with breather tape and closed with an end cap, and if algae is inside, the honest position is that it cannot be cleaned out effectively. Flushing sometimes helps a little; usually it means resheeting.
- Green inside is algae in the flutes
- Washing the surface will not touch it. This is why the roof still looks green afterwards.
- It enters at the sheet ends
- Failed or missing breather tape and end caps. That is the fault to fix, not the algae.
- It is not really cleanable
- Flushing occasionally helps. Mostly it means the sheet has reached the end of its life.
- Seal new sheet properly
- Breather tape and end caps at both ends. It is what determines whether this happens at all.
The box gutter is where the leaks are
Where a conservatory roof meets the house there is usually a box gutter or a lead flashing, and that is the detail that actually causes most conservatory leaks. It is also the part nobody cleans, because it is the hardest to see.
It fills with leaves and silt, ponds, and then backs up under the flashing. Clearing it is part of cleaning the roof rather than a separate job, and it is worth doing first because the debris from it ends up on the glazing anyway.
- Clear it first
- Whatever comes out of it lands on the glazing, so doing it first saves cleaning twice.
- It causes most leaks
- A blocked box gutter ponds and backs up under the flashing, and the leak looks like a roof fault.
- Check the outlet runs
- Water in at the top and out at the bottom. A blocked outlet is invisible from the ground.
- Look at the flashing while you are there
- The gutter is only accessible now, and a lifted flashing is easy to see with it empty.
Everything about not scratching it
Polycarbonate is soft. A grain of grit trapped in a brush head will draw a line across a panel that cannot be polished out, and a stiff brush will haze the whole surface over a few cleans.
So rinse the brush before it touches the roof, rinse the roof before you brush it, use soft bristles, and keep anything abrasive away entirely. No scouring pads, no glass scrapers, no household cream cleaners.
- Rinse first, brush second
- Grit on the surface is what scratches, carried by the brush. Wash the loose material off first.
- Rinse the brush too
- A brush that has been on the ground has grit in it, and it takes that grit straight onto the plastic.
- Soft bristles only
- A stiff brush hazes polycarbonate within a few cleans, and the haze is permanent.
- Nothing abrasive
- No pads, scrapers or cream cleaners. Mild detergent and water is what the sheet is rated for.
Frequently asked questions
- What tools do I need to clean a conservatory roof?
- A telescopic pole with a soft brush head, a hose or water fed pole for rinsing, a gutter scoop for the box gutter, a squeegee or microfibre head for glass, and mild detergent. A ladder set alongside if some of it cannot be reached from the ground.
- Can you walk on a conservatory roof?
- No. Polycarbonate sheet carries almost no point load and glazing bars are not walkways, so both give way. Falls through conservatory and rooflight glazing are a recognised cause of serious injury. Work from the ground with poles, or from a ladder set alongside.
- Can I use a pressure washer on a conservatory roof?
- No. It forces water past the seals into the roof, lifts the glazing bar cappings and gaskets so they no longer seat, and on polycarbonate it strips the UV coating that determines the sheet's lifespan. A soft brush and a hose cleans just as well.
- How do I get rid of green algae in polycarbonate roof panels?
- If the green is inside the hollow flutes rather than on the surface, cleaning the outside will not touch it. It entered through failed or missing breather tape and end caps. Flushing occasionally helps a little, but usually it means the sheet has reached the end of its life.
- What should I clean a conservatory roof with?
- Mild detergent in water with a soft brush, then a clean water rinse. Nothing abrasive, no scouring pads, no glass scrapers and no cream cleaners, because polycarbonate is soft enough that all of them leave permanent marks.
- How do I clean the gutter where the conservatory meets the house?
- With a scoop on a pole from the ground or from a ladder set alongside, and do it before the glazing rather than after, since the debris lands on the roof. Then flush it and check water comes out of the outlet, because a blocked box gutter causes most conservatory leaks.
- Why does my conservatory roof still look green after cleaning?
- Because the algae is inside the hollow flutes of the polycarbonate rather than on the surface. Surface washing cannot reach it. It got in through unsealed sheet ends, and it is not really cleanable once established.
- How often should a conservatory roof be cleaned?
- Twice a year suits most, in spring and after the autumn leaves. Clearing the box gutter matters more often than cleaning the glazing, since a blocked gutter causes leaks while dirty glazing only looks bad.
