Learning Center · Exterior Cleaning
Pressure Washing Roofs and Siding: What Is Safe and What Wrecks the House
High pressure cleans concrete and ruins shingles. This guide explains why an asphalt shingle roof is never pressure washed, what the shingle industry says to do about algae streaks instead, and how siding and the rest of the house are washed without pushing water where the walls are built to keep it out.
Updated October 12, 2026
Read This First
The short version
- Never pressure wash an asphalt shingle roof. ARMA says not to use a power washer on it, because high pressure is likely to damage the roofing.
- Granules stripped by a pressure washer are not a manufacturing defect, so a shingle warranty is not written to cover them.
- Black streaks are algae; ARMA says a bleach and water solution lightens them, and no scrubbing.
- Siding is washed from the top down at low pressure so water is never driven up under the laps.
To get cleaning matched to your surfaces, start with Get Help or call or text 512-575-5052.
Short version: 2 min. Full page: 6 min. Want the detail? Each section below opens with a tap, or switch to Full at the top to open them all.
Direct Answer
Is it safe to pressure wash a roof?
Not on an asphalt shingle roof, where the industry says not to use a power washer at all.
What the shingle industry says
The answer is in the manufacturers’ own guidance. The Asphalt Roofing Manufacturers Association, the trade body for shingle makers, says not to use a power washer or any type of brush or broom to clean algae from a roof surface, and that high pressure washing systems are likely to damage asphalt roofing. The granules on a shingle are its sun protection and its wearing surface. A pressure washer strips them, the damage is permanent, and it is often invisible from the ground until the roof fails early.
What that does to the warranty
A shingle warranty covers defects, not damage. GAF’s shingle warranty, for example, warrants the shingles against manufacturing defects and excludes damage from causes beyond normal wear, such as the impact of traffic on the roof or foreign objects. Granules blasted off by a pressure washer are not a defect, so do not expect a manufacturer to cover a roof that was washed that way. The Roof Shepherd does not pressure wash roofs, on any job, for this reason.
Roof Cleaning
What to do about black streaks on a roof
The streaks are algae; ARMA describes a bleach and water solution, rinsed, with no scrubbing and no power washer.
What the streaks are
The dark streaks are algae. ARMA names Gloeocapsa magma as the most common of several species that discolor roofs, and says it grows especially in warm, humid conditions, which describes most of Texas. It is a discoloration, not a leak, and on the homes we look at it shows most on the slopes that stay shaded and damp.
What ARMA describes
Low pressure and chemistry, not force. ARMA says the discoloration may be lightened by applying a solution of liquid household bleach, sodium hypochlorite, and water, that mixing directions may vary by shingle maker, that the surface should not be scrubbed because friction loosens granules, and that the effect is temporary. The trade calls this soft washing: the solution goes on at garden hose pressure, sits, and is rinsed. Plants below the roof are wetted and covered first. GAF’s warranty names the reasonable cost of commercially cleaning the shingles as its remedy for algae on products carrying its StainGuard label, which is one more sign that cleaning, not washing, is the accepted answer.
Ask for a look first
Streaks are a reason to look, not to blast. If the roof is old enough for algae, it is old enough to have other things going on. Ask for a documented look at the roof before any cleaning, so the record shows what was there before anyone touched it. Our roof maintenance guide covers what a yearly look includes.
Walls
How siding is washed without wrecking it
Top down, low pressure, a wide tip, and never spraying up under the laps or into the soffit vents.
The method
Water goes where the siding was built to shed it: down. Siding is washed from the top of the wall down with a wide fan tip held at a distance, at low pressure, with a cleaner for mildew where needed, then rinsed. Spraying upward drives water under the laps and behind the siding, where the wall is built to keep it out, and it can fill the soffit vents and the attic edge. Painted and wood siding get the least pressure of all, because high pressure gouges soft wood and lifts paint. Our pressure washing service matches the method to each surface.
The places to protect
Some parts of a wall cannot take any pressure. Window seals and glazing, door weatherstripping, old mortar joints, electrical fixtures and the gaps around hose bibs and vents are all places where concentrated water does harm. A wash plan names them.
Before paint
A wash is the first step of a paint job. Walls are washed to remove chalk, dirt and mildew so paint can bond, then left to dry fully before primer. Our exterior paint prep guide puts the wash in the full sequence.
Hard Surfaces
Where high pressure does belong
Concrete, stone and most masonry take high pressure well; everything else gets less.
Concrete and stone
Driveways, sidewalks, patios and most masonry are what a pressure washer was made for. A surface cleaner attachment keeps the pass even and avoids the stripes a wand leaves. Even here, old or soft mortar and sealed or stamped concrete are checked first.
Fences and decks
Wood gets a light touch. Fences and decks are washed at low pressure with a cleaner, in the direction of the grain, and left to dry before any stain. Too much pressure raises the grain and leaves fuzz that no stain hides. Our fence and deck staining guide covers what comes next.
Planning Range
What a house wash costs
A house and siding wash is a job price, and the roof is never on it.
The planning range
A house and siding wash runs $490 to $830 as a planning range for a single story home, with two story homes and heavy mildew at the top of the range or above it. Driveways, fences and decks are priced by the square foot on a visit. Roof washing is not on any of our price lists, because we do not do it. These are planning ranges, and a written quote settles the number.
Common Questions
Questions homeowners ask
Can you pressure wash an asphalt shingle roof?
No. ARMA, the shingle makers’ trade body, says not to use a power washer on a roof and that high pressure washing is likely to damage asphalt roofing. The granule loss is permanent. The Roof Shepherd does not pressure wash roofs.
How do you get black streaks off a roof?
They are algae. ARMA describes applying a solution of household bleach and water, with no scrubbing and no power washer, and notes the effect is temporary. The trade calls that soft washing.
Does pressure washing void a roof warranty?
A shingle warranty covers manufacturing defects and excludes damage from causes beyond normal wear. Granules stripped by a pressure washer are damage, not a defect, so a manufacturer is not going to treat them as a warranty claim.
Is it safe to pressure wash vinyl siding?
At low pressure, from the top down, with a wide tip and never spraying up under the laps. Driving water behind the siding or into the soffit vents is the damage to avoid.
How much does it cost to pressure wash a house?
Our planning range for a house and siding wash is $490 to $830 for a single story home. A written quote after a look settles the number.
Keep Learning