Roof Soft Washing: Black Streaks, Methods and Roof Care

Reviewed and updated October 6, 2026.

Identify the staining before choosing treatment

Brown or black streaks can be algae discoloration. The Asphalt Roofing Manufacturers Association (ARMA) distinguishes algae from moss and says there is no scientific evidence that algae damages asphalt shingles. Its guidance describes moss as a different concern that can lift shingle edges and interfere with drainage.

Photographs are a useful starting point, but a photograph of staining is not a roof-condition report. Tell the assessor about active leaks, missing pieces, loose shingles and previous repairs. Those observations change the work required. Cleaning should not be sold as a substitute for repairing an unsound roof.

What a suitable cleaning proposal should identify

ARMA's June 2024 technical bulletin says cleaning directions can differ by shingle manufacturer. It advises gentle application and rinsing, protection of the surroundings, and avoiding power washing or abrasive brushing that can remove granules. A generic pressure number does not demonstrate that a method is suitable.

• Roof identification: the material, manufacturer and product, where known.
• Condition: staining separated from moss growth, damage and existing leaks.
• Cleaning plan: the proposed product and instructions applicable to that roof.
• Property protection: access, nearby plants, adjoining finishes and the route of rinse water.
• Limits: what improvement is expected and what repairs or additional work are excluded.

Roof access and slippery treatment conditions make this work appropriate for trained professionals. You can provide photographs from the ground; there is no need to climb onto the roof to prepare a quote request.

Check the actual warranty

A contractor's use of the phrase “soft washing” does not prove that a proposed treatment meets your roof's requirements. Keep the shingle paperwork and ask which maintenance instructions the contractor will follow. If the product is unknown, resolve that question before agreeing to treatment. Do not assume that every shingle warranty requires periodic washing or that every cleaning method preserves coverage.

Set expectations for the result

ARMA notes that algae discoloration can recur after cleaning. The time between treatments needs to be considered for the individual property. Ask how the contractor will judge completion, whether further observation is needed and which remaining marks may be unrelated to organic growth.

Keep dated photographs of the agreed areas before and after the visit. If you see a new leak or displaced material, report that condition directly instead of assuming another wash will solve it.

Compare the scope of roof-cleaning quotes

For a Kitchener-Waterloo property, send the address, roof photographs, known material and the problem you want assessed. Include access restrictions, connected garages or additions, and any concerns about existing damage. A written quote should identify the treatment area and exclusions. D&D roof cleaning starts from $450; the written quote confirms the price for the agreed work.

Read the local roof-cleaning quote checklist, view our roof cleaning service, or request an assessment.

Roof soft-washing questions

Do black roof streaks mean I need a new roof?

No. Staining alone does not establish that replacement is needed. Roof condition, leaks and damage should be assessed separately before choosing cleaning or repair.

Can I use a pressure washer on asphalt shingles?

No. ARMA advises against power washing asphalt roofing. Ask for a cleaning method that follows the instructions for your actual shingle product.

Does soft washing automatically preserve my warranty?

The name of the service is not enough to establish that. Check the product's warranty and maintenance instructions against the proposed treatment before work begins.

Sources and reading

• ARMA: Algae Discoloration of Roofs, revised June 2024
• ARMA: algae and moss prevention and cleaning

Devon Moore, Operations Lead Co-Founder & Operations Lead, D&D Home Services

D&D Home Services is Kitchener-Waterloo's trusted exterior cleaning company. We've served hundreds of homeowners across Kitchener, Waterloo, Cambridge, and Guelph with professional, insured exterior services.