Perthshire’s climate is a paradise for moss. Damp, mild, and shaded by a great many mature trees. On a north-facing slate roof it will establish itself within a few years and it will keep growing.
Honestly? Less than the companies selling roof cleaning would like you to believe. A light growth of moss on a sound slate roof is doing very little harm, and we will tell you so rather than take your money. However, moss causes three specific issues that are worth taking seriously:
Moss acts like a sponge, keeping slates and joints permanently damp. In a Scottish winter, this water freezes — freeze-thaw cycles crack slates and break down mortar over the years.
Moss washes into gutters and clogs them. Overflowing gutters saturate exterior walls, creating damp issues that cost vastly more to fix than timely roof clearance would have.
Thick growth getting underneath the lap of a slate can, over time, physically lift it out of position, exposing your roof structure to direct water penetration.
We have been called out to fix roofs that were leaking for the first time in their lives immediately after being pressure-washed. It is a genuinely destructive practice on traditional Scottish roofs.
Working safely from proper roof access, working meticulously from the ridge downward to gently remove moss growth without disturbing slate fixings.
Thoroughly clearing the gutters and downpipes afterwards — ensuring water can flow freely off the building is the main objective of the exercise.
A specialized biocide treatment applied gently at low pressure where appropriate, penetrating spores to kill organic growth and slow down future regrowth.
Inspecting the entire slate field while we are working up there and providing clear, honest feedback about any secondary issues or defects we find.
Every three to five years on a shaded or north-facing Perthshire roof. Less on an exposed, sunny one.
Yes. It’s Perthshire. Biocide treatment slows it considerably, but nothing stops it permanently, and anyone promising otherwise is selling.
They genuinely do work — rainwater running over the metal carries ions down the roof that inhibit growth. They’re most effective near the ridge, they’re cheap, and they’re worth fitting if we’re up there anyway.
Maybe not. Call us and we’ll look. If the growth is light and your gutters are clear, we’ll tell you to leave it and save your money. We’d rather have your reroof in fifteen years than £250 today.
