IMO venting a dryer upwards through a and roof is a large mistake. Assuming your original laundry room (the now-pantry) had the machine on a exterior wall, then that was an ideal location for it. ALL dryer exhaust air contains lint particles and and the ductwork needs periodic cleaning. Mine is a straight shot of less than 12" out the wall and accumulates some lint residue around the louvers of the outside exhaust hood over the course of a year. Condensation occurs during cold weather inside ducting that passes through an unheated space (attic) which accelerates lint adhering to it.

You could get a condenser dryer that doesn't need a vent, like our Miele

There are also heat pump ventless machines from whirlpool that are full size capacity.

Dryer vents should not go up. It's a risk for additional build up and fire hazard. Put it through a wall or other space. It will make clean out easier.

I have a dryer on an interior wall & the vent goes out in the floor (crosses a room, that kind of thing)--every few years we get someone to do a vent-cleaning on that pipe--and of course it's not the flex-pipe!--but seems to work pretty well, we've had it...14 years now.

I think there is also a duct lenght maximum, but I'm too busy to search for it in the IBC.