Securing Vent Rise Above Roof

I've sized the vent for the 2 hot water tanks and I need 5" diameter B vent.
The vent must leave the basement and rise vertically to above the eve.
Can anyone recommend a good technique to secure the vent that is above the roof? Perhaps 2 pieces of rigid metal back to the roof will work but I'm wondering if anybody knows any tricks of the trade.

Thanks for any replies

secure

Use an FHA standoff clamp below the roof and a longer piece of class B so it reaches through the standoff. If you have a roof overhand, go through it with a standard roof jack/flashing around the pipe.

With B vent am I supposed to use 2 sheet metal screws per union or is that a no-no?