If you’re looking at black streaks, green cushions or crusty patches on your roof, you’re most likely looking at algae, moss or lichen. All three are common on tile and shingle roofs across the San Fernando, Santa Clarita, Conejo and Simi valleys. We remove them with a low pressure softwash, which is a cleaning solution applied gently, given time to work, and rinsed off. Estimates are free. Call (818) 913-1626 Monday through Saturday, 7am to 7pm, or request an estimate.
The rest of this page explains what’s growing on your roof, why, what it does, and what you can and can’t safely do about it.
What is growing on my roof?
Several different things get called “roof stains.” Here’s how to tell them apart.
| Growth | What it looks like | Where it shows up | How hard it is to remove |
|---|---|---|---|
| Algae | Black or dark streaks that run down from the ridge | Most common here. Often on shaded or north-facing slopes | Usually the easiest |
| Moss | Thick green or brown cushions | Shaded, damp spots, between tiles and along shingle edges | Moderate. Thick moss can take more than one visit |
| Lichen | Flat, crusty patches in gray, green or orange that grip the surface | Older, shaded or slow-drying areas | The slowest. Can take more than one visit, and may leave a faint stain |
| Mold and mildew | A dark or gray film | Shaded or damp areas, often with algae | Usually easy to moderate |
| Not growth | Rust drips, tar, mineral deposits, efflorescence on concrete tile, stains from trees | Below vents and metal, on tile surfaces, under trees | Varies. Some of it isn’t something a wash removes |
We can’t always tell what you have from a photo. Several of these look alike from the ground, and more than one can be on the same roof. We look at it in person and tell you what we see.
Why does it grow on my roof?
Almost all roof growth comes down to moisture. Anything that keeps the roof damp longer gives it a place to live.
- Shade from trees, tall walls or the house itself
- North-facing slopes that get little direct sun
- Overhanging branches and the leaf litter they drop
- Valleys, flat sections and low spots that hold water
- Irrigation overspray or gutter overflow that lands on the roof
- Some roofing materials that hold moisture longer than others
The dark streaks are commonly caused by an algae often called Gloeocapsa magma. It spreads down the roof in long lines, following the path rain water takes. On asphalt shingles, some fillers in the shingle can commonly feed it, which is one reason shingle roofs streak so readily.
Our climate has a pattern. Dry summers slow growth on sunny slopes, but it persists in the shade and under trees. After the first rains it can spread, and streaks often look darker after a wet winter.
Hillside and tree-lined streets make this more noticeable. A roof under oaks in Thousand Oaks or on a shaded lot in Calabasas stays damp far longer than an open, sunny roof in a newer tract.
Does it damage my roof?
Honestly, it depends on what’s growing and for how long.
Algae is mostly cosmetic early on. Over time a heavy coating holds moisture and heat against the surface, and it makes the roof look older and dirtier than it is.
Moss holds water against the roof. It can lift shingle edges and collect between tiles, which keeps those spots wet.
Lichen attaches firmly. Over many years it can wear the surface it’s gripping.
Growth can also hide a problem. A thick patch of moss can cover a cracked tile, and a dark stripe can sit over a worn spot. That’s one more reason to look at the roof once it’s clean.
So heavy growth can speed up wear. We won’t tell you it’s about to ruin your roof, and we can’t put a number on how many years it costs. If you’re worried about the roof’s actual condition, or about warranty terms, ask your roofer or check with the roof manufacturer. We don’t make warranty promises.
How do you remove algae, moss and lichen?
We softwash the roof. That means a cleaning solution applied at low pressure, time for it to work, and a rinse. The solution does the cleaning, so we don’t rely on force.
Different growth responds differently, so here’s what to expect.
| Growth | What we do | What to expect |
|---|---|---|
| Algae | Apply the cleaning solution, let it work, rinse | The roof looks cleaner once it’s rinsed and dry |
| Moss | Same softwash, with more time on thick areas | Thick moss can take more than one visit. We guarantee the removal and come back as many times as it takes |
| Lichen | Same softwash on the affected areas | Slowest to come off. We guarantee it comes off and come back as many times as it takes. The lichen will be gone, but the spot can keep a faint stain and may not look spotless |
| Mold and mildew | Same softwash | Usually comes off with the rest of the roof |
| Not growth | We assess it first | A wash may not remove rust, tar or mineral deposits. We’ll say so before we start |
We guarantee our moss and lichen removal. If it takes more than one visit, we keep coming back as many times as it takes. On lichen, the surface underneath can keep a faint stain, so we guarantee the growth comes off but don’t promise a spotless roof.
What happens on the day?
We start by looking at the roof, the access and the plants around the house. We rinse and protect plants and landscaping before and after we work. Then we apply the cleaning solution to the roof at low pressure, give it time to work, and rinse it off.
You’ll usually see the roof look better as it dries, and thicker growth can take more time. If moss or lichen needs more than one visit, we keep coming back as many times as it takes. You don’t need to be home.
Why not pressure wash, scrape or use bleach yourself?
We get it. The growth is right there and it looks easy to fix. It isn’t.
- Pressure washing can strip the granules off shingles, crack or chip tile and push water in under it.
- Scraping and wire brushes scratch and gouge the surface.
- Do-it-yourself chemicals can harm plants, stain walls and gutters, and leave the roof slippery.
- Ladders and roofs are dangerous. A wet, algae-covered slope is slick, and tile can break underfoot. Please don’t climb up there.
We’re insured and rope access trained, and we use the safest techniques we know for each roof. You can read more in our guide to roof algae and black streaks and pressure washing versus softwashing for roofs.
What about tile and shingle roofs?
Concrete and clay tile. Growth settles into the textured surface and the low edges where water runs. Tile can crack or chip under pressure, so we keep it gentle and careful. Mineral deposits and efflorescence on concrete tile can look like growth, and a wash may not remove them.
Composition shingle. Algae clings to the granule surface, and the granules are the shingle’s protective layer. That’s the main reason we don’t use force.
On every roof we assess before cleaning. We don’t repair roofs. If we notice a cracked tile, a lifted shingle or damaged flashing, we’ll tell you so a roofer can take a look.
How do I know it’s time to clean?
Most customers call when they notice streaks from the street or green patches along the shaded side. Earlier is easier. Light algae is simpler to remove than a thick mat of moss, and it’s a good moment to look at the roof before the rainy season starts. If you can see growth between tiles or along shingle edges, it’s worth having someone look at it.
You don’t have to wait for the whole roof to turn dark. Send us a photo of the shaded side and we’ll tell you what we think.
Roofs with solar panels
Panels and roof growth often share a roof. Dark streaks right below the lower edge of a panel are common because water runs off the glass and across the roofing, and growth can build up around and under the edges of an array.
We clean the roof around the panels. We never use the roof solution on the panels. They get cleaned separately by hand with deionized water, as described on our solar panel cleaning page, and we can do both in the same visit. If wildfire ash is part of the picture, see our guide on solar panels and wildfire ash.
How long until it grows back, and how do I slow it?
There’s no single answer. It depends on shade, moisture, trees and the roof material. A roof under oaks or on the shaded side of a hill will show growth sooner than a sunny, dry one. We won’t promise how long a roof stays clean, but we’ll tell you what we expect for your home.
A wet winter can speed growth up, and our El Niño 2026-27 guide covers what to watch for.
You can slow regrowth:
- Trim branches back from the roof so it gets more sun and less leaf litter
- Keep gutters and valleys clear so water drains instead of pooling (our gutter cleaning covers that)
- Fix drips and adjust irrigation that sprays the roof
- Clear leaf litter off the roof surface
- Let the sun reach the roof where you can
Some homeowners ask a roofer about zinc or copper strips near the ridge. We don’t install those.
What should I tell you before we come?
A few details help us give you a better estimate:
- Roof type: tile, shingle or something else
- How many stories the house is
- Photos of the worst areas
- Whether the roof has solar panels
- Access and gate details
- Pets on the property, and anything you want us to avoid
Roof cleaning plus other services
Since we’re already there, it makes sense to combine. House washing covers stucco, siding and trim. Gutter cleaning clears the debris along the roof edge. Bird proofing helps if birds are roosting on the ridge or nesting at tile ends, and cleaning comes first.
We clean roofs in Granada Hills, Porter Ranch, Woodland Hills, Calabasas, Thousand Oaks, Valencia, Simi Valley and across the rest of our service area. For more detail, read our guide to roof algae and black streaks.
All our work comes with a 100% satisfaction guarantee. If you’re not satisfied, we’ll come back and make it right at no additional cost. Request a free estimate or call (818) 913-1626.