Going to the soffet is 12 feet.
Vent bathroom fan through roof or wall.
Typically an exhaust fan that is vented through the roof has a roof hood or roof cap which allows air to exhaust but provides protection from wind blown rain.
The fan will need to be an inline fan with ducting and a grill in the bathroom.
Start in the attic and drill a hole through the roof in the desired vent location.
If you want to vent a bathroom fan through an exterior wall you will have to cut a 3 inch or 4 inch hole with a hole saw drill bit.
Try to keep it close to the fan location.
Choice is go up to roof 5 6 feet or out the present vent 15 18 feet with insulated pipe or shorten the line by going straight to side of home but this requires going up high with latter to drill a new vent hole as tight quarters in attic prevent drilling from attic.
Will be usually fed.
If your exterior siding is vinyl or fiber cement you will have an easier time cutting the hole.
In order to accomplish this the roof has to have a hole cut in it.
It is because of this that many builders tend to advise against this method.
These are usually installed on a pitched roof.
Broan sells an inexpensive model which is probably available at any big box store.
This involves running ductwork from the fan usually though an attic and out through the roof.
From up on the roof use a jigsaw or reciprocating saw to cut a 4 in.