Roof cleaning guides

Identify. Photograph the roof from the ground on each elevation. Moss is green and three-dimensional. Algae is flat black streaking, most often gloeocapsa magma per ARMA. Lichen looks like crusty patches bonded to the surface. Knowing which you have sets both urgency and price.

Choose the method. For asphalt shingles the answer is soft washing. ARMA's guidance is a cleaning solution applied, allowed to dwell 15 to 20 minutes, and rinsed thoroughly with low-pressure water — and never a pressure washer, brush, or broom. Get this in the contract, not just in conversation.

Hire. Verify liability and workers' compensation insurance directly from the insurance agency. Ask what fall protection the crew uses. Confirm landscape protection is in scope, since ARMA advises protecting landscaping and surrounding areas from the bleach solution. Sanity-check the price against Today's Homeowner's $255-$1,190 typical range.

Prevent. ARMA is clear that cleaning is temporary. The durable levers are trimming overhanging branches so sunlight and airflow reach the roof, keeping debris off, and metal ion sources — zinc or copper strips, which Malarkey notes work best installed at new roof installation, or algae-resistant shingles at your next re-roof.

How to choose

Do the identification step yourself

Ten minutes with a camera from the ground. It stops you being sold a moss-removal price for an algae-staining problem.

Put the method in the contract

"Soft wash only; no high-pressure equipment on the roof surface." That sentence is your recourse if granules end up in the gutter.

Verify insurance before scheduling, not on the day

Certificate direct from the insurance agency. On the day, you are already committed.

Trim the branches — it is the highest-return step

Shade and debris are the cause. A tree trim reduces every future cleaning and every future moss problem.

Plan algae resistance into your next roof

ARMA notes algae-resistant products are commercially available and designed to inhibit growth for extended periods. That is a specification decision at re-roof time, and it costs far less than repeated cleaning.