Cleaning a green, dirty or yellowed polycarbonate roof

A polycarbonate roof that has gone green or grey is usually just dirty, and you can clean it. One that has turned yellow, brown or cloudy has a different problem: the plastic itself has broken down in sunlight, and no amount of scrubbing will bring it back. Work out which you have before you spend an afternoon up a ladder.

Green, dirty or yellow: which do you have?

What you see	Likely cause	Can you clean it?
Green or black film, moss at the edges	Algae or moss growing where the roof stays damp and shaded	Yes, from outside
Grey film, leaves, bird droppings	Dirt and debris	Yes
Streaks or growth inside the sheet	Water and dirt in the hollow flutes	No, the sheet needs new end tapes or replacing
Misting inside the flutes	Condensation that cannot drain out	Sometimes: check the tape at the bottom of the sheet
Yellow, brown or cloudy all over	The plastic degrading in sunlight	No

A quick test: look at the underside from inside the room. If the colour is the same from inside and out, and a wet cloth does not change it, it is in the plastic, not on it.

How to clean a polycarbonate conservatory roof safely

1. Stay off the roof. ConservatoryLand says you should not walk on a polycarbonate conservatory roof, and Ultraframe says it is not safe to stand directly on any conservatory roof.
2. Work from a ladder. Ultraframe notes that special ladders can be hired for conservatory roof maintenance.
3. Clear leaves and gutters first. Which? names blocked gutters as a common cause of roof leaks, so this is worth doing even if the roof looks fine.
4. Wash with warm soapy water and a soft brush or sponge on an extending pole, working down the slope along the line of the flutes.
5. Rinse with clean water so no soapy film is left to attract dirt.
6. Skip anything abrasive. Check the sheet maker’s care advice before using anything stronger than soapy water.
7. Clean the inside with a damp cloth from a stepladder.
8. Check the fittings while you are up there: bar caps, end caps and gutter joints. Loose caps and blocked gutters are where leaks start. Our roof maintenance guide has a fuller checklist.

If you would rather pay someone, Checkatrade’s 2024 refurbishment guide puts a professional deep clean at around £12 per roof panel.

If the growth or misting is inside the sheet, cleaning the surface will not reach it. Polycarbonate sheets are meant to have solid tape at the top and breather tape at the bottom, so any condensation in the flutes can drain out. When those fail, water and dirt collect inside, and the sheet needs new tapes or replacing. For more on misting, see conservatory condensation.

Why do polycarbonate roofs turn yellow?

Sunlight, and especially its ultraviolet part, slowly breaks down the plastic. The sheet changes colour, lets through less light and becomes more brittle, which is also why old roofs crack and leak. How fast depends on the sheet and its UV protection, and published estimates vary widely:

Source	Stated lifespan of polycarbonate
Little Conservatory Company (installer)	Degrades and discolours within 5 to 10 years
The Eco Experts (review site)	Around 10 years
ExpertSure (review site)	Around 10 to 15 years before discolouring
MyHomeImprovements (review site)	10 to 15 years with proper maintenance
ConservatoryLand (installer)	10 to 20 years
WholesalePOS (sheet retailer)	25 to 30 years for 16mm to 25mm multiwall

Notice the pattern: firms selling replacement roofs quote shorter lives and the firm selling sheet quotes longer ones. No independent lifespan study was found. One retailer’s example warranty covers 10 years against discolouration of more than 20% light loss, so if you re-sheet, ask exactly what the discolouration warranty covers. Our guide to how long a conservatory roof lasts compares all roof types.

What to do when the sheets have yellowed

You have four options, from cheapest to dearest:

Option	What it involves	Typical cost, medium conservatory
Insulated panels	Opaque panels in the existing bars	£1,800 to £4,600
New polycarbonate	New sheets in the existing bars	£2,700 to £5,200
Glass	Usually a new roof designed for glass	£3,500 to £7,000
Tiled	A new insulated solid roof	£7,400 to £12,100

Re-sheeting is the like-for-like fix. The caps come off, the old sheets come out, the bars and seals are checked, and new sheets go in with the flutes running downhill and the right tapes at each end. One couple’s DIY account of re-sheeting a lean-to with 25mm multiwall put the materials at £324, with two people working a full day. Think about the specification while you are at it: on Ultraframe’s figures, 35mm sheet loses less heat than 25mm (U-value 1.3 against 1.7), and opal, bronze or Solarguard tints let through far less of the sun’s heat than clear sheet. Our guide to polycarbonate thickness compares the options, and new polycarbonate roof costs has prices.

The catch is that new polycarbonate brings back everything else about polycarbonate: hot in summer, cold in winter and loud in the rain. If those bother you, a glass roof, insulated panels or a tiled roof cost more but fix them too. Glass is heavier, so the frames need checking; LABC notes that frames built for polycarbonate may only have enough reinforcement for that load. See conservatory roof costs to compare.

When you get quotes, ask each installer to name the sheet or glass it will fit, its thickness and tint, and what its guarantee says about discolouration.