Roof cleaning comparisons

The comparison is unusually one-sided on asphalt shingles, so we will not pretend otherwise. ARMA's guidance is explicit: "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." Manufacturer guidance agrees — Malarkey warns that pressure washing dislodges the granules that are a shingle's primary defense against damage and UV aging.

On price, pressure washing wins and that is the trap. EcoWatch's 2026 numbers put high-pressure washing at $0.15-$0.60 per square foot and soft washing at $0.30-$0.80. You save a few hundred dollars now on a roof that may need replacing years early. That is not a saving.

Chemical-only wash is the cheapest of all at $0.15-$0.30 per square foot per EcoWatch. It can be appropriate for light algae staining where no rinsing pass is needed, but be clear on what you are buying: a treatment, not a clean. Ask whether the roof is rinsed afterward, because ARMA cautions against letting the solution dry completely on the surface.

Manual moss removal is the most expensive at $0.60-$1.00 per square foot per EcoWatch. Sometimes it is necessary on heavy growth. Ask how it will be done — ARMA warns against scrubbing with brushes or brooms because friction loosens and removes granules, so "manual" should mean careful lifting after treatment, not scrubbing.

How to choose

On asphalt shingles, soft wash is the only method to accept

ARMA's position is unambiguous. Any contractor proposing high pressure on shingles is either untrained or hoping you do not know.

Do not confuse "low pressure" with "soft wash"

Ask for the PSI at the surface and whether a chemical solution with dwell time is used. A low-pressure rinse without the chemistry just moves the algae around.

Metal and tile are different conversations

Method suitability varies by material. Ask the contractor to justify their method against your specific roof material and, where you have it, the shingle manufacturer's own care guidance.

Weigh the price gap against roof replacement cost

The difference between the cheapest and safest method is a few hundred dollars on a typical roof. Premature roof failure is tens of thousands. The comparison is not close.

Ask about the rinse

ARMA advises rinsing thoroughly with low-pressure water and cautions against letting the bleach solution dry completely. A no-rinse service is a different product.