Roof venting is very common. Wouldn't hesitate a moment, especially with that saving in distance. If you have flat or composite-shingle roof, sealing it up properly is pretty easy. If you have slate or other tile, it can be kind of a chore. The folks at Lowe's or HD have everything you need.

Bill_h,
This is very typical in town homes. I work for Whirlpool and we have a formula for all of our dryers. You may want to check with your Brand on their venting requirements. Our formula is that the dryer will vent 60 ft straight for every 90 degree turn you will need to subtract 10 feet. Take the difference and you have the length of vent acceptable. We do sell one dryer that can vent longer do to a different motor but all the rest have this requirement.
Good luck
Jon_M

If you live in a winter snow & ice climate venting through the roof doesn't sound great. Deflecto and others make vent caps made specifically for roof installations. What do you mean by, "theres a vent directly above where the pipe would go through the ceiling to the roof vent only 2.5 ft"? A dryer vent shouldn't be shared with anything else. The other consideration is that lots of lint make it past the dryers lint trap. If your vent termination in on your roof, this is where this extra lint will end up.

theres a aluminum roof vent, in the roof. would it be ok to just let the vent pipe vent out of it? or do i need a dedicated vent for the dryer?

"theres a aluminum roof vent, in the roof. would it be ok to just let the vent pipe vent out of it? or do i need a dedicated vent for the dryer?"

Leave the existing vent alone. It serves another purpose. Dryer vents should not "share" with anything else. You need "dedicated" vent for the dryer.

Your even asking these questions tells me you're over your head. Suggest either obtaining specific instruction for the task or hiring an experienced, knowledgeable person to do it for you.

Jon-M, which dryer is it that Whirlpool makes for longer vent runs? Is it the new Cabrio? I know its twin, top of the line Oasis, has the dual motor; does Cabrio also have it and is this what you're talking about?

asolo, the experienced, knowledgeable, contractor i had look at it was the one who wanted to run a flex pipe to the existing roof vent! didnt sound good to me, but says he does it all the time. so much for him haha. myself i was thinking 4 inch rigid alum through the ceiling, and roof to a dedicated roof vent. but the condo assoc. wont let me do it myself, so on goes the search for a haha " experienced, knowlegeable," person know anyone in the detroit area??? that fits the bill???

bill h.....your contractor is an idiot!

Shared duct? Flex-pipe? Does this "all the time"? He is a crook as well as a fool! Get him out of your life.

Your task is not complicated. HD, Lowes or any of them will tell you everything you need to know to do it correctly. They probably have booklets about the topic as well as all items needed. From your last post, all you'll need is this personal knowledge plus an honest contractor willing to do the job correctly. Rigid ductwork. Dedicated vent. Appropriate roof exit and sealing. Every good wish to you.

stumbled across this thread, reviving to comment that any time you run duct in an unconditioned space (ie your attic), you need to insulate the duct and caulk all penetrations. otherwise the exhaust air condenses on the inside of the duct when it hits the cold attic, and lint builds up. in extreme cases, with enough condensate you can cause water leaks at duct joints. you insulate to keep the exhaust air toasty warm all the way to the point it exits the building.

Ok so we started remodeling our home last year and then money ran out! we created a laundry closet in our hall which was an improvement from the dryer being on the back porch.... lol.
BUT now and i run the dryer and the vent is a few ft of flex tube the connects to a useless lint cathcing box! Results....HOT HUMID AIR FILLS MY HOUSE and the lint is covering the walls in the laundry closet...which by the way also holds the water heater! yeah i know FIRE HAZARD! so....I need some tips on the least inexpensive way to solve the obvious issues at hand. Oh and a few more tid bits of info....there is a square hole in the celing above the washer and dryer (im assuming it was for ventilation for the water heater???) and....I LIVE IN PHOENIX where its already 90 degrees in MARCH!

This thread is old, but still seems relevant.
I've looked elsewhere on this subject, but don't see good answers to my situation.

My dryer sits in the middle of my townhouse on the 2nd (top) floor. The dryer vent goes up through a wall from near floor level, and currently terminates at the floor in the attic with no outside vent!! It is pretty near the center of the attic. There are units to both sides of me, and the roofs are complex, alternating pitch from unit to unit.

My options for how to route the vent all seem poor. I can't go horizontally between the attic floor joists to the side of my unit, because that would take me into my neighbor. I could go parallel to the attic floor and out the back wall. But that would be a long run (15' in the attic plus the run up to the attic and the turn. And it would have to be over the joists. That seems problematic since I use the attic for storage. And it gets cold there, so I'm worried about condensation in such a long run.

Or, I can go pretty much straight up through the roof. The vent is very near the center line, so it would have to jog at least a little bit to go out to the side of the ridge. That would be the shortest run - about 8' from the attic floor. But I live in MA, so I'm worried about what happens when it snows. This last winter we had *lots* of snow, and lots of ice dams. What happens if the roof vent is entirely covered in snow? Will the dryer melt through the snow? (It will probably be less of a problem if the vent is near the ridge. Snow doesn't often remain there for very long.) I came across a product by dryerjack.com that has a version for "moderate" snow, but apparently not for 2' of snow.

Of course right now the dryer is venting into the attic, which contributes to the ice dams, so almost anything is likely to be an improvement.

Another concern I have is cleaning the vent. If it is up on the roof it will be very difficult to access to clean. I have no equipment to get up there. Even exiting on the end wall two stories up would be a problem, but somewhat less so.

I have seen pictures of inline lint traps. If I could put one of those in the attic then I would be able to clean it out more easily. But would that add too much back pressure?

I have a neighbor who cleans dryer vents by blowing them out (from the inside) with a leaf blower. But doing that would be logistically difficult. I would have to move the dryer well out of the way. It is a gas dryer, and I think I would have to disconnect the gas to move it far enough. I guess I could potentially disconnect the vent inside the attic and blow it out from there, though that would do nothing for the part in the laundry wall.