How-to · 4 min read · Updated 6 November 2026
How to clean uPVC fascias, soffits and conservatory roofs safely
Why uPVC goes green and black
uPVC is smooth and largely maintenance free, but it is not dirt free. Fascias, soffits and gutters sit at the edge of the roof where water runs off, so algae, dirt and black streaks from traffic and rain build up. Conservatory roofs, especially polycarbonate ones, collect leaves, moss and algae in the channels and along the glazing bars.
Black streaks on gutters, sometimes called tiger stripes, are usually caused by dirt and pollution carried by water running over the edge. Green growth is algae, usually worst on shaded sides.
Grey or white chalky marks on older uPVC are usually surface weathering of the plastic itself rather than dirt, and they need different treatment.
What to use and what to avoid
| Use | Avoid |
|---|---|
| Mild detergent or uPVC cleaner | Abrasive pads and scouring powders |
| Diluted biocide for algae, as per the label | Strong solvents such as acetone or thinners |
| Soft brushes and microfibre cloths | Wire brushes and stiff bristles |
| Low-pressure rinsing | High-pressure jets close to seals and joints |
| Long reach poles from the ground | Standing on conservatory roofs |
Abrasive cleaners and solvents can dull the surface of uPVC and remove its protective finish, making it stain more easily in future. Some cleaning products sold for uPVC restoration are fine for occasional use, but test any new product on a small area first.
Step by step for fascias, soffits and gutters
- Clear leaves and debris from gutters first so water can run freely
- Close nearby windows and protect plants below with water and sheeting
- Apply the cleaner or diluted biocide with a low-pressure sprayer or soft brush
- Leave it for the time stated on the label
- Agitate stubborn black streaks gently with a soft brush
- Rinse with low-pressure water, working from top to bottom
- Check that downpipes are clear and gutters are draining
Professionals often use water-fed poles and soft brush heads to reach first and second floor rooflines from the ground, which avoids ladders and protects the roof edge.
Check fascias and soffits for damage as you clean. Cracked boards, loose cover trims and missing soffit vents are easy to spot once the surface is clean and are much cheaper to fix early.
Conservatory roofs
Conservatory roofs are not designed to take a person's weight. Polycarbonate sheets crack, glass can break and glazing bars can bend. Clean them from the outside using long reach poles and soft brushes, or from a ladder or platform positioned so that no weight goes on the roof itself.
Clear leaves and moss from the gutters and glazing bar channels first. Treat algae with a mild cleaner or diluted biocide, rinse gently and avoid letting strong solutions sit on seals and rubber gaskets for longer than needed.
Glass conservatory roofs with self-cleaning coatings need extra care, because harsh cleaners and abrasive brushes can damage the coating. Follow the glass manufacturer's guidance where you have it.
Cladding and composite panels
Many homes have uPVC or composite cladding around bay windows, dormers and gable ends, and modern homes increasingly use composite or fibre cement boards. These are cleaned in a similar way to fascias, with low-pressure biocide treatment and gentle rinsing. Timber cladding needs more care, as strong mixes can lighten the wood or affect stains and oils.
Common mistakes
- Using a stiff brush or scouring pad, which scratches and dulls the surface
- Applying solvent-based products that soften or discolour uPVC
- Leaning ladders on gutters, which can crack brackets and joints
- Cleaning in hot sun, which leaves streaks as products dry
- Spraying high pressure upwards into soffit vents and under roof tiles
- Forgetting to clear gutters first, so dirty water overflows again
If uPVC is very old and already chalky or yellowed, cleaning will improve it but may not make it look new. In that case, specialist restoration products or replacement may be the longer-term answer, but cleaning is always the first step.
How often to clean
For most homes, cleaning fascias, soffits and gutters every one to two years keeps them looking good and helps spot problems such as leaking joints, sagging gutters and damaged soffit boards early. Combining it with gutter clearing and a render or roof soft wash in the same visit is usually more cost-effective. As a guide, cleaning the outside of fascias, soffits and gutters on a typical house usually costs £100 to £300.
Frequently asked questions
Can I pressure wash uPVC fascias?
Light pressure from a distance is unlikely to harm solid uPVC, but high pressure close up can force water behind fascias and into the roof space, damage soffit vents and blow out gutter seals. It also does not kill algae, so growth returns quickly. A low-pressure biocide treatment with soft brushing usually gives a better and longer-lasting result.
How do I remove black streaks from white gutters?
Black streaks are usually ingrained dirt and pollution rather than growth. A dedicated uPVC or gutter cleaner applied with a soft brush or cloth, then rinsed, usually removes them. Avoid abrasive pads and solvents, which damage the surface. Very old streaks may need a couple of treatments. Clearing the gutters stops dirty water overflowing and causing new streaks.
Why is my conservatory roof turning green?
Polycarbonate and glass conservatory roofs often turn green because leaves and debris collect in the channels and stay damp, allowing algae and moss to grow. Overhanging trees and shade make it worse. Regular clearing of gutters and channels, followed by a gentle cleaner or diluted biocide and low-pressure rinsing, keeps the roof clear and lets more light through.
uPVC fascias soffits conservatory
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