Practical notes on keeping a roof alive west of the Cascades — written for the weather we actually get.
In a drier state moss on a roof looks untidy. West of the Cascades it is the thing that ends the roof early — and pressure-washing it off makes matters worse.
Leaves sit on top of each other and let water through. Douglas fir needles interlock into a mat that does not. That is why gutters here block in October.
Age, the state of the deck underneath, and how many places are failing at once. Those three answers decide it — not the size of the stain on your ceiling.
Water runs along the underside of the sheathing and down a rafter before it drops. The hole is regularly several feet uphill of the stain.