Black streaks on gutters are mostly carbon and road grime carried down by rainwater, sometimes called tiger stripes. Green is algae that grows where the roofline stays damp and shaded. Both build up slowly over years. They can be washed off by hand with the right cleaner and a soft brush, without pressure.
What are the black streaks on gutters?
Mostly airborne grime. Soot, exhaust film and dust settle on the roof. When it rains, water runs down the tiles and over the edge of the gutter, carrying that grime with it. It dries in vertical lines on the front of the gutter, which is why the streaks are often called tiger stripes.
Homes near busy roads, or with a lot of overhanging trees, tend to get them worst. They're stubborn because the grime bonds to the plastic over time.
Why do fascias and soffits go green?
Algae, just like on a conservatory roof. Fascias and soffits that face north, sit in shade or stay damp give green algae a place to grow. It starts as a thin film and gets thicker year by year. It's most common under deep eaves, behind trees, and on bungalows near hedges.
Is it a sign of a problem?
Usually not, but sometimes. Streaks and algae are mostly cosmetic. But a heavy, concentrated stain in one place can mean a gutter is overflowing there, from a blockage or a joint that's dropped. If you see a dark streak running down the wall below the gutter, it's worth checking the gutter is clear and draining.
Does rain wash it off?
No. The front of the gutter and the face of the fascia are vertical and sheltered, so rain doesn't clean them. In fact, rain is what puts the black streaks there in the first place. Once the grime has bonded, only cleaning will remove it.
How do you clean uPVC fascias and gutters?
By hand, with a soft brush and a uPVC-safe cleaner, then rinse. Apply the cleaner, give it a minute to work, and brush gently along the length of the board. Rinse with plenty of clean water. For high rooflines, a soft brush on a water-fed pole reaches from the ground. Stubborn black streaks may need a second pass.
What should you avoid?
- Pressure washers: they can force water behind the fascia and into the roof space, and damage the finish.
- Abrasive pads: they leave dull, scratched patches that go dirty faster.
- Bleach and strong solvents: they can mark the plastic and harm plants below.
- Leaning ladders on gutters: use a stand-off or rest them on the wall.
How long does it stay clean?
Usually a good while, but it does come back. The causes are still there: the road, the trees, the shade. Cleaning before the stains get heavy makes the next clean quicker. Cutting back overhanging branches helps the green.
What about the windows underneath?
Do the roofline first. Anything washed off the fascias and gutters runs down onto the frames, sills and glass below. That's why a deep clean works top to bottom: roofline, then frames, then glass, then sills.
Our frames, sills and fascia deep clean takes the whole front of the house back to white in one visit across Essex, by hand and with soft brushes, no pressure washer.