Those black streaks running down your roof tiles are not dirt. They are colonies of algae and lichen that feed on moisture and minerals, and they will keep spreading until they are treated properly. At Outdoor Butler we remove them from roofs across Villamartin, Orihuela Costa and Torrevieja using a gentle soft wash treatment that kills the growth at the root, without a pressure washer ever touching your tiles. Ask us for a free, no obligation quote today, with no hidden fees.
What are the black streaks on my roof tiles?
The main culprit is a hardy blue-green algae called Gloeocapsa magma, usually mixed with lichen and mould. The algae builds a dark protective coating to shield itself from the sun, which is exactly what you see as those grey-black streaks. Colonies start on the dampest, shadiest part of the roof, typically the north-facing slope, and gravity slowly drags them downwards, leaving the tell-tale vertical stripes from ridge to gutter.
The spores are airborne, so once one roof in the street has them, the neighbouring roofs usually follow. If several villas in your urbanisation show the same streaks, that is why.
Why the DIY method fails
Most homeowners reach for one of two things: a pressure washer or supermarket bleach. Both cause more problems than they solve.
A pressure washer blasts the visible black off, but terracotta and concrete tiles are brittle and porous. High pressure cracks tiles, strips the protective surface layer, and forces water underneath the tiles and into the roof structure. The algae roots survive inside the pores, so the streaks come back within months, often worse, on a roof that is now more absorbent than before.
Bleach poured or sprayed from a ladder runs off before it can work, kills your plants below, corrodes gutters, and leaves you balancing on wet tiles. Walking on a tiled roof is dangerous for you and for the tiles, which crack underfoot far more easily than people expect.
How roof streaks are actually removed
- Inspection first. We check the tile type, condition and fixings, and identify any cracked tiles before any treatment starts.
- Protection. Gutters, downpipes, plants and anything below the roofline are protected or pre-rinsed.
- Soft wash application. A professional biocide solution is applied at low pressure, similar to heavy rainfall. It soaks into the pores of the tile and kills the algae, lichen and mould at the root.
- Dwell time. The solution is left to work. Lichen and stubborn colonies die off and release their grip on the tile.
- Gentle rinse or natural weathering. Depending on the surface, we rinse at low pressure or let the weather carry the dead growth away over the following weeks, leaving the tiles clean and undamaged.
How to keep the streaks from coming back
Because the treatment kills the organism rather than just stripping the stain, a soft washed roof typically stays clean for around three years, often longer on concrete tiles. Trimming back overhanging branches, keeping gutters clear and treating the shaded slope before the streaks take hold all extend that further. A periodic maintenance treatment is far cheaper than replacing cracked or crumbling tiles.
The Costa Blanca angle
Roofs here have their own set of enemies. Coastal humidity and morning dew keep north-facing slopes damp even in summer. Calima dust settles on the tiles and acts as a nutrient layer for algae. And most local roofs use curved terracotta tiles, the classic teja, which are beautiful but especially fragile under pressure and quick to absorb moisture once their surface is worn. That combination is exactly why soft washing, not pressure washing, is the right method on the Costa Blanca. It is the same logic we explain in our guide to professional pressure washing services: the right method for the right surface.
Frequently asked questions
Are black streaks harmful to my roof?
Yes, over time. The algae holds moisture against the tile and feeds on its surface, and lichen roots slowly break up the material. Left alone, streaks shorten the life of the roof, not just its looks.
Can I pressure wash roof tiles?
We strongly advise against it. High pressure cracks tiles, strips their protective surface and pushes water into the roof. Soft washing achieves a deeper, longer-lasting clean with none of the damage.
How much does roof cleaning cost in Spain?
It depends on the size, pitch, access and condition of the roof, which is why we quote each roof individually. The quote is free, there is no obligation, and there are no hidden fees.
How long will my roof stay clean after treatment?
Around three years is typical, and often longer. Shaded, tree-lined or very humid plots may need treatment a little sooner.
Get your roof looking new again
If your roof in Villamartin, Orihuela Costa or Torrevieja has black streaks, send us a photo and we will tell you honestly what it needs. Message us on WhatsApp at +34 644 466 783 or call +34 644 390 864 for your free, no obligation quote. No hidden fees, just a roof you can be proud of.