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Roof Cleaning FAQ
Why Does My Roof Look Dirty? 7 Questions Kankakee and Will County Homeowners Ask
Every summer we get the same call. A homeowner in Bourbonnais or Frankfort walks to the mailbox, turns around, looks up at the house, and notices the roof has gone dark on one side. It looked fine last year. This article answers the seven questions those homeowners ask us most, in plain language, with no sales pitch buried in the middle.
The Short Answer
Your roof does not look dirty because it is dirty. It looks dirty because something is living on it. The dark vertical streaks are a cyanobacteria called Gloeocapsa magma that feeds on the limestone filler in asphalt shingles. The soft green mounds are moss , which holds water against the shingle and lifts the edges. The pale gray or green crust that looks painted on is lichen , which bonds into the granule surface. All three take hold on the shaded, north facing slopes that most Kankakee County and Will County homes have, and none of them rinse off with a garden hose. A low pressure soft wash removes all three at the root without stripping granules, without a pressure washer touching the shingles, and without voiding a shingle warranty.
1. Why does my roof look dirty when it is only ten years old?
Roof age has almost nothing to do with it. Staining is driven by moisture and shade, not by how many years the shingles have been up there. A seven year old roof under a mature oak will streak long before a twenty year old roof in full sun.
What you are looking at arrived as airborne spores. They land on every roof in the region. On a slope that dries out fast in the sun, they never get established. On a slope that stays damp for hours after a rain, they colonize, spread, and start feeding.
Our part of Illinois gives them a lot to work with. Humid Kankakee River corridor summers, heavy tree canopy through the older Kankakee and Bourbonnais neighborhoods, spring pollen that adds an organic food layer, and a freeze and thaw cycle that keeps roofs wet through late winter. Homeowners here often see the first faint streaks somewhere between year five and year eight.
The practical takeaway: a stained roof is a maintenance item, not a sign that the roof is failing. Most of the roofs we clean have years of service life left. See how the process works on our roof cleaning service page.
2. What are the black streaks on my roof, and are they damaging the shingles?
The black streaks are colonies of Gloeocapsa magma, a cyanobacteria. It is dark because it grows a protective sheath that shields it from UV light. It feeds on the limestone filler used in asphalt shingles, so it is consuming part of the shingle, though the damage is slow.
The streaks run downhill because rain carries the colonies down the slope, which is why the pattern looks like something spilled at the ridge and dripped toward the gutter. Light colored shingles show it first. Weathered wood and driftwood colors hide it the longest, which is why some homeowners are surprised when we point it out.
On the damage question, be honest with yourself about the timeline. In the first few years the growth is a curb appeal problem. Over a longer stretch it does three things that matter:
- It holds moisture on the shingle surface, and standing moisture is what invites moss and lichen, which cause real physical damage.
- It darkens the roof, so the surface reflects less sunlight and the attic runs warmer in July and August.
- It reads as deferred maintenance to appraisers, buyers, HOA boards, and insurance underwriters, whether or not the shingles are sound.
That last point costs homeowners more money than the first two combined. We wrote about the HOA side of it in our guide to Frankfort HOA curb appeal standards.
3. Why is only one side of my roof streaked?
The stained slope is almost always the north facing one, or the one shaded by trees. It gets the least direct sun, so it stays damp the longest after rain, dew, and snowmelt. The south slope dries within an hour and the growth never gains a foothold.
Once you know this, you start seeing it on every street. Drive through a Manteno or New Lenox subdivision where the houses all face the same direction and the same roof plane is stained on the entire block. That is not a coincidence and it is not a shingle defect.
Two other patterns worth knowing:
- Clean stripes below flashing. If you see a clean vertical band running down from a chimney, a roof vent, or a metal valley, that is zinc or copper washing off the metal in the rain. Those trace metal ions suppress growth on everything below them. It is the same principle behind zinc strips installed near the ridge.
- Heavy growth under overhanging limbs. Branches drop debris, block sun, and drip water in the same spot for years. Trimming them back is the single best free thing a homeowner can do to slow regrowth.
4. Is the green fuzzy stuff moss, and is it worse than the black streaks?
Yes, and yes. Algae stains the roof. Moss and lichen damage it. Moss anchors itself into the seams between shingles, holds water like a sponge, and lifts shingle edges as it thickens. Lichen roots into the granule layer and takes granules with it when it finally releases.
Homeowners use "moss" and "mold" for anything green on a roof, which is fine in conversation but not much help when deciding what to do. Here is how to tell the three apart from the driveway.
Algae
Flat dark streaks running down the slope. No texture. No height. Cosmetic first, but it is the moisture layer everything else grows in.
Moss
Raised green clumps, usually along shingle seams, in valleys, and at the north edge. Spongy when wet. Lifts shingles and traps water underneath.
Lichen
Crusty gray, white, or pale green rosettes that look painted on. The hardest of the three to remove and the one that pulls granules if scraped.
A proper soft wash treats all three the same way: apply the solution, let it dwell, kill the organism at the root, then rinse at low pressure. Moss and lichen do not vanish the moment the truck pulls away. They die, dry out, turn brittle, and shed over the following weeks of rain and wind. That surprises people, so we say it up front on every roof job.
★★★★★
"Unmatched customer service! Stellar. Arrived at agreed time & got right to it. Reasonably priced, too. Cleaned the awful moss & mold from my roof, it looks sooo much better."
Jacqueline McTaggart
Read all 95 Google reviews for Green Pro Services5. Can I just pressure wash the roof myself?
No. The Asphalt Roofing Manufacturers Association warns against using a pressure washer, a brush, or a broom on asphalt shingles. High pressure blasts off the ceramic granules that shield the asphalt from UV light. The roof looks clean for a season and then ages fast.
Granules are not decoration. They are the sun shield. Once they are gone the asphalt underneath bakes, dries, and cracks, and no cleaning brings them back. We have inspected roofs in this area where a single DIY pressure washing session took years off the life of the shingles, and the giveaway is always the same: clean, faded lines where the wand tracked back and forth.
Three other reasons homeowners hand this one off:
- Chemistry. Roof cleaning solution needs the right dilution, the right surfactant, and the right dwell time. Too weak and the growth returns by fall. Too strong, or applied without pre wetting and rinsing the landscaping, and you kill the shrubs along the foundation.
- Falls. A wet, treated roof is one of the most slippery surfaces on a residential property. Roof work is the reason our crew completed OSHA 1910 safety training before anyone touched a ladder.
- Runoff. The rinse has to be managed so it does not sheet into gutters, downspouts, and beds unchecked. That is a planning step, not an afterthought.
Pressure has its place. It belongs on concrete. Our pressure washing page explains which surfaces we clean with pressure and which ones we never touch with it.
6. Will roof cleaning void my shingle warranty?
A low pressure soft wash does not void a shingle warranty. Pressure washing can. Shingle manufacturers and ARMA point homeowners toward a sodium hypochlorite and water solution applied without pressure, which is exactly what a professional soft wash is.
The confusion comes from lumping every kind of roof cleaning together. There are two very different jobs on the market and one of them is a problem:
- Soft washing. Solution does the work. Water pressure at the shingle is close to what comes out of a garden hose. This is the manufacturer aligned method.
- Pressure washing a roof. Force does the work. It strips granules, can drive water under shingle courses, and gives a manufacturer a reason to deny a claim.
If you want the paperwork side buttoned up, pull your shingle manufacturer's care and maintenance document and read the cleaning section. Then ask any contractor you are considering one direct question: what PSI reaches the shingle? If they cannot answer it, keep calling. We are happy to put our method in writing before we schedule.
7. My insurance company sent a letter about my roof. Does cleaning it fix that?
Often, yes, when the letter cites algae, moss, mildew, or biological growth rather than structural damage. Insurers now review roofs with aerial and satellite imagery and flag staining as deferred maintenance. Cleaning the roof and sending back before and after photos with a paid invoice resolves many of these notices.
A few things worth understanding before you respond to one of these letters.
Non renewal is not cancellation
Cancellation ends a policy in the middle of its term. Non renewal means the carrier will not write it again when the term ends. Most roof related notices are non renewal, and carriers have to give written notice and a reason. That notice usually carries a response window of 30 to 60 days, so the date on the letter matters more than anything else in it.
The imagery is not always right
Aerial and satellite review is a snapshot from directly above. Shadows get read as damage, a neighboring roof gets attributed to the wrong address, and normal weathering gets flagged as growth. Homeowners have successfully appealed these notices with a documented inspection showing the roof was fine. If the letter does not match what you can see from the ground, ask the carrier for the image they are working from.
Documentation is the whole game
If the growth is real, the response is straightforward. Get the roof cleaned by a licensed and insured contractor, keep dated before and after photos from the same angles, and keep the paid invoice showing the address, the date, and the service performed. Send that package to your carrier before the deadline on the letter.
We provide all of it as a matter of course on roof cleaning jobs, and we can provide a certificate of insurance on request. We are not insurance agents and this is not insurance advice, so call your agent about your specific policy. What we can tell you is what the carrier is looking at, because we clean the thing they photographed.
Two more questions we hear every week
How often should a roof be cleaned in Kankakee or Will County?
Most homes in our area go 3 to 5 years between roof cleanings. Homes with heavy shade, mature trees overhead, or a north slope that never dries usually land closer to every 2 to 3 years. If you can see faint streaks starting to return, that is the right time to schedule, because early growth clears faster and cheaper than a roof that has gone another two seasons.
What does roof cleaning cost?
Price follows roof size, pitch, access, and how much growth is present. A single story ranch with light streaking and a two story home with moss packed into every valley are different jobs. We quote most roofs in this area the same day using Google Earth, without an appointment or a site visit. Give us the address and what you are seeing, and you get a real number back. You can also start with our power washing price estimator for a ballpark before you call.
Should I do anything else while the truck is here?
Roof runoff lands in the gutters, so most homeowners pair a roof cleaning with gutter cleaning and a house wash. If you are getting ready to list, the roof is one of the first things a buyer sees in a drone photo. Our guide on pre listing exterior cleaning covers the order we recommend.
Where we clean roofs
Green Pro Services is based at 407 S. Yates Ave in Kankakee and cleans roofs across Kankakee County, Will County, and the south Cook suburbs. No travel fees inside our service area.
Send Us a Photo of Your Roof
Text a picture and your address to (815) 650-0397 and we will tell you what is growing up there and what it takes to remove it. Most quotes come back the same day, no appointment needed.
