What Holds It Up
What holds the trough to the house is the single biggest factor in how long it stays there, and Toronto ice load is what tests it.
Short answer
A hidden hanger clips inside the trough and screws into the fascia, spreading the load and holding against thermal movement. A spike and ferrule drives through the trough into the fascia and works loose over years. Spacing matters as much as type, and in an ice climate closer is better.
Why spikes fail
Thermal movement. The trough expands and contracts along its length and the spike is driven across that movement, so it walks out.
The hole it leaves in the fascia lets water in, which is how the fascia rot starts.
A spike relies on friction in a single hole rather than on a screw thread.
The ferrule is the only thing stopping the trough being crushed, and when the spike loosens the ferrule does nothing.
Ice load pulls directly on the spike with no mechanical advantage.
And once one has backed out, the neighbouring ones carry more and follow.
What a hidden hanger does differently
It clips over the front bead and under the back of the trough, so it holds the shape as well as the position, and it fastens with a screw rather than a driven nail. The load path is better, the fastener holds, and there is no hole through the face of the trough. It also looks better, because nothing is visible from the ground.
Spacing
The standard spacing is a maximum rather than a target.
Closer spacing on a run with ice history, on a long run, and on a run under a valley discharge.
Closer at corners and at the outlet, where the load concentrates.
Closer where the fascia is marginal, which spreads the load across more fasteners.
And closer where a ladder will inevitably be leaned near the trough, however much everybody intends not to.
The extra hangers are a trivial cost relative to rehanging a run that pulled off.
What the fastener goes into
Solid fascia, which has to be established before anything is hung. Soft or rotted fascia holds nothing.
Screws long enough to reach through capping and into the board, which on a capped fascia is a specific consideration.
The sub-fascia or the rafter tails where the fascia itself is marginal, which is the proper repair rather than a longer screw into soft wood.
Not into the capping alone, which is thin aluminum and is the common shortcut on a repair.
And with drip edge in place, because that is what keeps water off the fascia the fasteners are relying on.
Common questions
Are spikes and ferrules acceptable?
They work loose with thermal movement and leave a hole in the fascia. Hidden hangers are the standard.
How close should hangers be?
Closer than the maximum, especially on runs with ice history or a valley discharge.
Can they screw into the capping?
No. The fastener has to reach solid wood.