· Michael Blair
Siding is not waterproof and was never meant to be. Water gets behind it routinely, and what keeps the wall dry is the weather barrier and flashing underneath. When those are wrong, the siding looks fine for years while the sheathing goes.
Where water gets in
Around windows and doors, where flashing either directs water back out or does not. Missing or reversed head flashing over a window is the single most common defect.
Then at roof-to-wall junctions without a kick-out flashing, which sends a roof’s worth of runoff straight down inside the wall at one point.
Signs visible from outside
Paint failing repeatedly in one area regardless of repainting. Siding that is soft when pressed, particularly low on the wall and under windows.
Staining below a window corner, and a bulge or wave in the siding plane where sheathing has swollen and lost strength.
- Repeated paint failure in one spot
- Soft siding below windows or at the base
- Vertical stain lines below window corners
- A wave or bulge in an otherwise flat wall
- Fasteners backing out or rust bleeding through
The kick-out flashing problem
Where a roof edge meets a wall, water running down the roof needs to be kicked away from the wall into the gutter. A missing kick-out puts it behind the siding at that exact point.
The damage is concentrated and severe — often a rotted stud bay and sheathing behind apparently perfect siding. It is worth checking every roof-wall junction on the house.
What a proper repair involves
Opening the wall to sound material, replacing sheathing and framing as needed, then correcting the flashing and weather barrier before any siding goes back.
Siding replaced over the same defective detail rots again. If a quote does not mention flashing or house wrap, it is a cosmetic repair with a countdown on it.