Roof Cleaning: Why This Job Should Be Left to Professionals
Your roof protects almost everything underneath it.
It protects your family, your belongings, your walls, your ceilings, and the structure of your home.
It is also one of the most expensive exterior surfaces to repair or replace.
That's why roof cleaning is different from cleaning a driveway, patio, or even the siding on your house.
Perfectly Clean™ Rule
Homeowners should understand how their roof is cleaned—but roof washing is a job we recommend leaving to trained professionals.
In this chapter, we're going to teach you what those black streaks on your roof may be, why roofs become dirty, how professional roof cleaning works, what methods can cause damage, and what you should look for when hiring someone to clean your roof.
What we're not going to do is give step-by-step instructions for climbing onto your roof and cleaning it yourself.
There are simply too many things that can go wrong.
Why Shouldn't I Clean My Own Roof?
There are several risks involved with roof cleaning.
The first and most obvious is falling.
Roofs can already be dangerous to walk on.
Now add:
Water + cleaning solution + algae + moss + a sloped surface
and the risk can increase quickly.
Even experienced exterior-cleaning professionals need to carefully consider how a roof can be cleaned safely.
But falling isn't the only concern.
DIY roof cleaning can also involve:
Damaging shingles
Using the wrong cleaning solution
Using too much pressure
Damaging gutters
Sending cleaning solution into landscaping
Improper chemical handling
Walking on areas that should not be walked on
Sending water underneath roofing materials
Damaging surrounding siding, windows, or painted surfaces
That's why this is one area where knowing how the process works is more valuable to most homeowners than knowing how to perform it themselves.
What Are the Black Streaks on My Roof?
You've probably seen them.
A roof that was once one consistent color starts developing long, dark streaks.
Sometimes one side looks much worse than another.
Those dark streaks are often associated with biological growth on the roofing surface.
You may also see other types of growth, including moss or lichen.
Moisture and shade can play a major role in how quickly these conditions become noticeable.
Trees can also contribute by creating shade and dropping organic debris onto the roof.
Just like the siding on your house, different areas of your roof can age and collect growth differently.
Why Is One Side of My Roof Dirtier?
Look at your roof throughout the day.
Some areas may receive hours of direct sunlight.
Others may remain shaded by:
Trees
The shape of the house
Other roof sections
Nearby buildings
Areas that stay shaded can remain damp longer after rain or morning moisture.
And remember what we learned earlier:
Moisture + shade + time can create favorable conditions for organic growth.
That's why you may see one roof slope covered with dark streaks while another looks much cleaner.
Should You Pressure Wash Asphalt Shingles?
This is where the name pressure washing can confuse homeowners.
You may hire a pressure-washing company to clean your roof.
That does not mean the company should treat your roof like a concrete driveway.
Asphalt shingles are not concrete.
A roof-cleaning process should be selected specifically for the roofing material.
Aggressive high-pressure cleaning can damage roofing materials and should not be used as a shortcut for removing roof growth.
At Pro Wash Pressure Washing, our roof-washing process is based on low-pressure chemical application, not blasting asphalt shingles with high pressure.
The goal is to treat the growth without using unnecessary mechanical force against the roof.
How Does Professional Roof Cleaning Work?
The basic idea is actually similar to what you've already learned about soft washing.
Instead of relying on high-pressure water to physically blast growth from the roof, an appropriate roof-cleaning solution is applied at low pressure.
The cleaning solution does the work.
The professional controls:
The solution → The application → The runoff → The surrounding property → The result
But roof cleaning requires additional planning because everything applied to the roof eventually has to go somewhere.
And that's where property protection becomes extremely important.
Where Does the Cleaning Solution Go?
Imagine applying water to the top of your roof.
Where does it go?
Down.
It can travel into:
Gutters
Downspouts
Flower beds
Grass
Bushes
Trees
Porches
Decks
Driveways
Walkways
That's why a professional roof cleaner shouldn't only be looking up.
They also need to know what's happening below.
Before the roof is cleaned, the property should be inspected and a plan should be made for protecting the surrounding areas.
Plant Protection Is Extremely Important
If you've read the earlier chapters, you already know how seriously we take plant protection during house washing.
With roof cleaning, it becomes even more important.
A professional should identify the landscaping surrounding the house before the cleaning begins.
Special attention should be given to:
Flowers
Bushes
Grass
Potted plants
Delicate landscaping
Areas near downspouts
Fresh water can play an important role in protecting vegetation before, during, and after the cleaning process.
The crew also needs to pay attention throughout the job.
Plant protection isn't something you do once and then forget about.
Perfectly Clean™ Rule
If you're cleaning the roof, you also need to be thinking about everything underneath the roof.
What About Gutters and Downspouts?
Gutters collect water from your roof.
That means they can also affect where roof-cleaning runoff travels.
Before cleaning, a professional should understand:
Does the house have gutters?
Where do the downspouts discharge?
What's underneath those downspouts?
Is there landscaping nearby?
Where will the runoff travel?
These questions are part of the process.
A roof-cleaning company that pays attention only to the shingles and ignores everything below them is missing an important part of the job.
What About Moss and Lichen?
This is another area where homeowners can accidentally cause damage.
Suppose you see a thick patch of growth attached to your roof.
Your first instinct might be:
“I need to scrape that off.”
Or:
“I need enough pressure to knock it loose.”
That's not necessarily the right approach.
Some growth can be strongly attached to the roofing surface.
Trying to aggressively scrape or blast it away can cause unnecessary damage.
Depending on the type and severity of growth, professional treatment may kill the growth first, while the remaining material loosens and changes over time.
That means a professionally treated roof may not always look completely different the instant the application is finished.
A reputable company should explain the expected result before the job begins.
Should Someone Walk on My Roof?
Sometimes roof access may be necessary.
Other times, the roof may be cleaned using equipment that reduces how much roof walking is required.
The right decision depends on:
Roof pitch
Roof condition
Roofing material
Height
Access
Weather
Equipment
Safety conditions
There isn't one answer that applies to every house.
But homeowners should understand that walking on a roof carries risk for both the worker and the roofing material.
A professional should choose the safest practical method for the specific property.
What Should You Ask a Roof-Cleaning Company?
You don't need to understand every piece of professional equipment.
You just need to ask good questions.
“How are you going to clean my roof?”
They should be able to explain the process.
“Are you going to use high pressure on my shingles?”
For asphalt-shingle roof cleaning, aggressive high-pressure blasting should be a major concern.
“How will you protect my plants?”
They should have an answer.
“What happens to the cleaning solution coming through my gutters and downspouts?”
Again, they should have a plan.
“Will all of the moss or lichen disappear immediately?”
A trustworthy contractor should set realistic expectations.
“Are you insured?”
When someone is working around your roof and property, this is an important question.
Warning Signs to Watch For
Be cautious if someone tells you:
“We just turn the pressure up and blast it clean.”
That's not how a delicate roofing surface should be approached.
Also be cautious if a contractor:
Doesn't inspect the property
Doesn't ask about water access
Ignores the landscaping
Has no plan for runoff
Cannot explain the cleaning method
Makes unrealistic promises
Treats every roof exactly the same
Cannot explain what happens with moss or lichen
Doesn't appear concerned about weather or safety
A professional process should sound like a process.
Why Weather Matters
Roof cleaning doesn't happen in a bubble.
Weather can affect:
Chemical dwell time
Drying
Runoff
Overspray
Worker safety
Plant protection
Wind can move spray where you don't want it.
Extreme heat and direct sunlight can affect how quickly surfaces dry.
Rain can change the way cleaning solution moves across the roof and property.
A professional needs to evaluate the conditions rather than simply cleaning because the appointment is on the calendar.
Why More Chemical Isn't Automatically Better
This follows the same principle we've discussed with pressure.
If some cleaning solution works, that doesn't mean:
More chemical = better cleaning.
The correct process depends on the roof, the growth, the product being used, surrounding surfaces, landscaping, weather, and other conditions.
Professional roof cleaning involves understanding those variables.
It should never be:
“Let's make it as strong as possible.”
The goal is:
Use the appropriate treatment to achieve the desired result while protecting the property.
Why We Don't Teach DIY Roof Washing
Throughout the Perfectly Clean™ Guide, we're happy to teach homeowners.
We want you to understand your property.
We want you to understand what a professional is doing.
And when a project can reasonably be performed by a homeowner, we want you to understand the basic process.
But there's an important part of being educated:
Knowing when not to do something yourself.
Roof washing combines working at height, slippery surfaces, chemical handling, expensive roofing materials, runoff, and landscaping protection.
For us, the risk isn't worth encouraging homeowners to climb onto their roofs and experiment.
So our recommendation is simple:
Leave roof cleaning to a properly trained and insured professional.
You can still be an educated customer.
In fact, after reading this chapter, you should be better prepared to choose the right professional.
The Perfectly Clean™ Roof-Cleaning Standard
As a homeowner, you don't need to know every technical detail.
Look for these things instead:
INSPECTION
The roof and surrounding property are evaluated first.
CORRECT METHOD
The cleaning process matches the roofing material.
LOW PRESSURE
The contractor isn't treating shingles like concrete.
PROPERTY PROTECTION
Plants, gutters, downspouts, siding, and surrounding areas are considered.
CONTROLLED APPLICATION
The cleaning solution is applied intentionally.
REALISTIC EXPECTATIONS
The contractor explains what will happen with streaks, moss, and lichen.
SAFETY
The crew treats roof access and chemical handling seriously.
FINAL INSPECTION
The job and surrounding property are checked before leaving.
Perfectly Clean™ Quick Lesson
BLACK ROOF STREAKS
Often → Biological growth
MOSS OR LICHEN
→ May require treatment and time
ASPHALT SHINGLES
→ Do not treat like concrete
HIGH PRESSURE
→ Not the answer for asphalt-shingle roof cleaning
PLANTS BELOW
→ Must be considered and protected
DIY ROOF WASHING
→ We recommend leaving it to trained professionals
The Perfectly Clean™ Principle
Knowing how something should be cleaned doesn't always mean you should clean it yourself. Sometimes the right process begins with knowing when to call a professional.