I have added a small second story addition on my house that enclosed a
roof vent for my kichen sink. The contractor plans on installing what
he called a "cheat vent" because it vents into the attic. He will of
course have to extend it up a few feet to get into the new attic space.
It does not require him to punch a hole up through the roof. He said
it has a spring like flipper on the top that only opens when air is
being sucked. His reasoning for this is that he wants to minimize the
number of cuts into my roof because of its low pitch. It is almost a
12:4. I already have my chimney, two roof vents and a bathroom vent
poking through and have never had an issue.

My question is, do these things work adquetely, this is a kitchen sink
and I do not want it to be a slow drainer? Will it add moisture to my
attic? I have a very dry attic and have worked hard to vent exhaust
fans and other items outside of the attic. Any reason why I should not
let him use this type of "cheat" vent?

Thanks for all your help.
John