Yes but have you seen evidence for this i.e. old moss removal revealing higher than expected broken slates/tiles etc. ?
Yes..We live in an area with 99% of the houses having slate roofs ( Brittany ). In Ireland a large part of my home area had / has slate roofs.I know Wales very well, most of the houses in North Wales have / had slate roofs.
When you re-roof with slate , you remove the old ones ( I have done this many times ) where there was moss on the old ones , when you remove the moss, the slates show pitting , splits , and "flaking" damage.Unless your slate roof has been damaged by hailstorms or other percussive events, the absolute top reason for repairing it or replacing it is due to damage and or breaking of or displacement of slates due to moss damage.
Jacob..put down the spade and quit digging, you are making yourself look stupid in the face of the wide experience" of others here in the matter, I only posted this so as to avoid anyone falling for your usual stubbornness ( on this subject ) in the face of facts ( which does you no favours ) , anyone with a slate or tile roof following your thinking on the subject of moss on roofs would have to deal with the effects of moss damage long after you were gone.
Yes it looks picturesque ( I am a professional artist / sculptor , have been for 50 years ) but the charm ceases when a slate or a tile comes off or is broken due to moss damage and your roof leaks.My immediate neighbours had to replace their slate roof 5 years ago, the cost was horrific, nearly 25% of what they paid for the house.
We are in an area of slate quarries ( all now closed ), I also know the slate quarries at Blaenau Ffestiniog very well ( I think most , if not all of of them are now closed for roofing slate supplies, I used to buy slate discs by the tens of thousands from them for screen printing my designs on back in the 70s and 80s, I've talked at length with slate quarriers in both Wales and Brittany. Now some slate comes from Portugal, most is imported from India* ( as is the case with a huge amount of "decorative stone" ) when you go the now non working quarries , you can see the damage done by moss to the rock in situ, and if you have replaced slates or an entire slate roof because of damage due to moss being left to attack them, you would not be stubbornly talking such bolleaux.
When moss is growing and when it breaks down, it produces acids upon contact with water, said acids attack ( slowly ) whatever it is growing on**.
How do I know this ? A degree ( along with my arty ones ) in organic chemistry and experience, and experimentation.
* Not very "green" shipping slate halfway around the world to replace those slates and rooves damaged by allowing moss to grow on slate rooves.
added..you know Jacob , politically you and I are not so far apart ( as anyone can tell from some of the "likes" I "click"..but seriously , your stubborness on things that others know more about than you, or who have differing but equaly valid viewpoints on, would try the patience of a saint.Not an "attack", it's what I'd say to you if we were having a drink, you post some great stuff, very interesting and informative, and some like this.Go and plane something.
