Roof and deck soft washing in Southfield.
No pressure on the shingles.
The people who make asphalt shingles say never to put a pressure washer near one. They also publish the method that works instead, and it is the method used here.
A referral service for Southfield homeowners. An automated assistant answers; calls are recorded.
Typical cost: $250 – $600 for a roof, about three hours; deck $120 – $240 — national ranges (HomeGuide's national chart, June 2025)
- Cost to call
- Nothing
- Answered by
- Automated assistant
- Hours
- Any hour
Never a pressure washer
“Never use a pressure washer to clean an asphalt shingle roof as this will cause granule loss and very likely premature failure of the roof system.” That is the roofing manufacturers' own wording, and their algae page repeats it: high pressure washing systems are likely to damage asphalt roofing and should not be used to remove algae, or for any other purpose (on moss and algae · on algae).
What they publish instead is a low pressure wash: a 50:50 mix of laundry strength liquid chlorine bleach and water, applied with a sprayer, left on the surface fifteen to twenty minutes, then rinsed off thoroughly with water at low pressure (the method).
The same guidance notes the cleaning makes a roof slippery, and encourages the use of professionals for the work (the method).
Streaks and moss
Two different growths, and only one of them is a roof problem.
The black streaks are algae
The common one is an algae that protects itself from ultraviolet light by producing a dark pigmented sheath — which is the streak you see. By the time it is visible it has usually been up there several months or longer.
The roofing makers say there is no scientific evidence that algae damages asphalt shingles, although it certainly affects how the roof looks (on algae).
Moss is the one that matters
Moss grows on the parts of the roof that face north, which get less direct sun and stay damp longer — the shaded side of the house.
It lifts and curls the leading edges of the shingles, which raises the risk of blow-off in wind; in severe cases the build-up moves water sideways, which can damage the roof deck or cause leaks (on moss).
Keeping it off
Four things, in the roofing association's own order (on moss and algae).
- Trim branches back so sunlight reaches the roof.
- Clear debris with a leaf blower, not with anything abrasive.
- Keep the gutters clear, so water is not held against the roof edge.
- Do not let an upper gutter drain onto a lower roof.
And one thing not to do: the same guidance says adding zinc or copper strips to an existing roof is not recommended — exposed nails leak, and sliding strips under shingles breaks the seal (on moss and algae). It is worth knowing before someone offers it.
Cost
National ranges, not Southfield quotes.
Ask the contractor for your number in writing before any work starts.
Washing a deck and sealing a deck are two jobs with two prices. If the deck is being stained, the siding beside it gets covered first. The full table.
Algae is a looks problem. Moss is a roof problem.
The roofing manufacturers say there is no scientific evidence algae damages shingles, while moss lifts the shingle edges and raises the risk of blow-off. on algae · on moss
Ask which one is on your roof before you agree to anything. On the shaded north side, assume moss and look.
Questions
How long does a roof take?
- A national chart puts a professional roof clean at about three hours, at $250 – $600 (HomeGuide, June 2025). A steep pitch adds about $0.10 a square foot to it.
Will the bleach kill my plants?
- It is the reason the rinse matters: the solution has to come off the roof and go somewhere, and in Southfield that somewhere is not the storm drain (the city's own rule). Ask how the beds below the eaves are being protected and where the runoff is being sent.
When can this be done?
- Cleaning with water alone wants 40 °F and rising and ideally a week without a freeze after it (the brick industry's guidance). The two nearest weather stations with long records give 50/50 freeze dates of April 28 and October 17 at the Oakland County airport and April 18 and October 30 at Detroit City Airport — airport readings, not Southfield ones (the freeze normals).
Will I be charged for the visit?
- Calling us costs nothing. Some contractors charge to come out and look at the job. Ask before they come, and get the price in writing.