Your welcome !!
From the photo I can see the rake for three rows, I can`t tell from the lichens how thick the butts of the shingles are. I can see that each row goes under the one above it and four inches under the third. I`m guessing 6 inch exposed, 6 inches under the one above it, 4 inches under the third. 16 inches is a R/R half inch butt. These would be sidewall shingles, not reccomended for roofing.
At the butt (the thickest part) it rests a little under half the length of the shingle below it, this is a little more, not much, than a quater inch thick. When the shingle is worn, water can soak all the way through this part, and be under the exposier. This will cause WARPING, CUPPING AND WEAKNESS.
My concern for damage to your roof is NOT the product to be used. It is the forces used to scrub, weight of the stageing and people traffic. That weak spot can snap easily. Then you need to repair those, potentially damageing others in that process.
The proper ROOF SHINGLE from wood roofing has a ONE INCH BUTT, and allows for 8 inch exposier, 8 inches under, and 4 under the third. (max. exposier) (min.Five) These are 20 inches high and tapper down to one eighth, not zero like sidewall shingles. You have a half inch under each butt.
Again, I can`t tell from the photo, but sidewall shingles will always, always, always, give you problems. They`re NOT ment for roofing.
All wood roofing shingles have either three quarter butts (5") or one inch butts (8") Never use sidewall shingles (Halfinch)
Be careful to make sure scrubbing and traffic/weight is kept to a minimum, and good luck !!