Apply a bead of asphalt roof cement on the bottom of the vent.
How to vent two bathroom fans through the roof.
In order to accomplish this the roof has to have a hole cut in it.
A single exhaust exits through the roof figure a.
The master bathroom and the 2nd bathroom vent through the roof and through the same opening.
From inside the attic drive a nail through the roof directly above the bathroom vent fan.
To vent a bath fan through the roof you must first prepare a ductwork connecting the roof top to the bathroom.
Slide the vent under the shingles so they cover the top half of the vent flange.
The lower half of the flange sits on top of the shingles.
This involves running ductwork from the fan usually though an attic and out through the roof.
Over there mount the vent hood using tri polymeric locking seal paste and put the nails to strengthen it.
A grille in each bathroom attaches to ducts which then fasten to a y connector at the fan.
Center the nail between two rafters.
This system is quiet too.
Choosing a whole house fan.
Through the roof depending on the location of the bathroom it may be easy to vent the exhaust fan through the roof.
You mount a switch in each bathroom.
The 2nd bathroom vent drips on the floor and is ruining the ceiling.
This setup requires an in line centrifugal fan mounted in the attic drawing air simultaneously from both bathrooms see photo.