Soffit And Fascia
Rotted fascia behind an eavestrough is the most common finding on a Toronto eavestrough job, and capping over it is the most common mistake.
Short answer
Fascia rots because water gets behind the trough — from ice, from a missing drip edge, or from a trough sloped wrong. Soffit rots from the same water and from attic moisture. Capping rotted wood in aluminum hides it, traps the moisture and lets the rot continue out of sight, which is how a board becomes a rafter tail.
Why it rots here
Water getting behind the eavestrough rather than into it, which is the main cause, and which comes from ice, missing drip edge or wrong slope.
Ice sitting against the fascia all winter.
Attic moisture condensing at the eave, which wets the soffit from inside.
A blocked soffit vent, which means the eave cannot dry.
Eavestrough fasteners penetrating the fascia and letting water in at each hole.
And paint failure, which on an old Toronto house with wood fascia starts the whole process.
Why capping makes it worse
Aluminum capping over rotted wood seals the moisture in and removes the one thing that was allowing it to dry. The rot continues invisibly, reaches the rafter tails and the roof sheathing edge, and the eventual repair is structural rather than cosmetic. Capping sound, dry wood is fine. Capping wet rot is burying it.
What to check
Press the fascia behind the trough with a screwdriver. Soft or crumbling means rot.
Look at the soffit from below for staining, sagging panels and gaps.
Look for peeling paint and dark staining on the fascia face.
Check the rafter tails where they are visible, because the rot travels back along them.
Check the roof sheathing edge from inside the attic at the eave.
And check whether the soffit vents are open, because a blocked eave stays wet.
The proper repair
Remove the eavestrough and the existing capping to see the actual condition.
Replace rotted fascia and sub-fascia, and sister or repair rafter tails where they have gone.
Replace rotted soffit, and keep or restore the venting rather than covering it over.
Fit drip edge, which is the measure that stops the cause recurring.
Rehang the trough with hidden hangers into solid wood, at the correct slope.
And deal with the attic heat loss, because the ice that started this comes from there.
Common questions
Can rotted fascia just be capped?
No. Capping seals the moisture in and the rot continues out of sight.
What causes it?
Water getting behind the trough — from ice, a missing drip edge, or wrong slope.
How far does the damage go?
Frequently to the rafter tails and the sheathing edge. Check from inside the attic.