The correct way to vent a bathroom fan through an attic is to terminate the vent either to the roof or to the gable wall.
Install bathroom vent into attic.
One in line centrifugal fan can be mounted in the attic to exhaust the moisture from two bathrooms.
The attic bathroom will need electricity to supply at least two 20 amp gfci outlets and one switch controlled ceiling light.
Install bathroom electrical circuits.
When venting a bathroom exhaust fan make sure to vent the air to the outside rather than into your attic where it can cause mold and mildew to form.
Use an extra long 3 8 inch diameter spade bit to bore a reference hole through the ceiling and into the attic.
Remove your old exhaust fan.
Turn off the breaker box.
Each fan vents separately out the roof.
You might have to remove a few screws to get it out.
Dangers of wet bath exhaust vent air re entering the attic.
Now where the discharge point is is going to be up to you.
For optimum performance locate it between.
This involves running ductwork from the fan usually though an attic and out through the roof.
See details at bathroom vent codes.
Bathroom exhaust fans are not required by most codes.
You should never exhaust the bathroom fan directly into the attic.
Bathroom exhaust fans perform an important function by removing excess moisture from your home.
That will take it from the bath exhaust fan to a discharge point.
Either way the vent will have to go directly to the outside and installed with a vent hood cover.
A lot of options.
In order to accomplish this the roof has to have a hole cut in it.
So what you want to do is you want to install a duct a vent duct and you can use flex duct for this.
Measure the vent fan.
It is because of this that many builders tend to advise against this method.
Depending on the location of the bathroom it may be easy to vent the exhaust fan through the roof.
Your attic is not a temperature controlled environment is never the same temperature as your living space and generally closer to the temperature outside.
Drill a reference hole draw a mark on the bathroom ceiling where you d like to install the vent fan.
Use a circuit tester to ensure that the power is turned off.
These are easy to use and can be purchased at most home improvement stores.
Do not spill bath vent air into the building attic or roof cavity where it will condense on and damage building insulation roof sheathing possibly framing and where it will certainly encourage mold growth.
Both bathrooms are vented by a single in line fan that has one exhaust vent running through the roof.
Remove the grill cover.