Sodium hypochlorite (bleach) Referred to as SH for short, household bleach is the most commonly used roofing cleaning chemical, as it is the preferred cleaning agent of almost all pressure washing companies in North America. The chemical most used by roof cleaners today is still “bleach” or sodium hypochlorite. It's also the chemical of choice for ARMA, the Asphalt Roofing Manufacturers Association, ¹ But it's no longer true to say that today's roof shingles are mostly made of asphalt. Asphalt shingles are mainly cleaned by chemical means.
Using a load-bearing force to scrub or scrape the shingles is not a good idea and will only exacerbate the wear and tear of the shingle itself, further shortening its lifespan. There are several recommended cleaning products, but it's usually best to use a bleach mixture. Cleaning a roof is much cheaper than completely or even partially replacing it, which, of course, is expensive. It is also the preferred product for cleaning hardwood roofs and is where the process was expanded to now include asphalt shingle roofs.
Sodium hydroxide cleans dirt, mold and algae, but cleaning solutions must be used at adequate dilution rates and with a limited time, and must be thoroughly rinsed at high flow rates, but not at high pressures, to remove the chemical and thus stop any residual action. And it doesn't mean that sodium hydroxide products can't be used to clean many types of roofing materials. My uncle mentioned to me last night that he expects their roof to be cleaned due to dirt and leaves and asked me if I have any idea what the best option is. If your ceiling has black stripes, white “spots” called lichens, or moss growing on it, then it needs to be cleaned.
You can also use bleach with chlorine and water to clean the ceiling, since the sodium hypochlorite in chlorine bleach is effective in cleaning algae, fungi and moss. After spraying the roof and having blown it off, removing all the remaining debris from the roof, you can rinse it thoroughly. Whichever method you choose to remove stains from the ceiling, keep in mind that roofing is a hazardous job with a high accident rate. Limestone is one of the main reasons why Magma Gloeocapsa, or roof algae, has become a more noticeable problem for homeowners and a boon for roof washers.
However, undiluted bleach can damage the metal roof covers, gutters and drain outlets connected to the roof. I appreciate that you mentioned that it's important to keep your roof clean so you can have it for many years and it will serve you and your family. It also changes the water flow to the roof, which can damage any porch or roof covering you have. One thing I really liked is how you mention why people need chemical roof cleaning in the first place.
A bleach mixture to clean asphalt shingles will not damage the roof and will clean most types of roof damage.