I think that in the winter when temps are below freezing you will end up with ice on your plants ;) I also don't think the humidity is going to help much, if at all, in an open air environment as the effect will only last as long as the dryer is running. Likewise, once the clothes are dry, if the dryer is still running the air won't be humid anymore. Keep your lint trap clean or you will have incredibly dusty plants too ;) In other words I think this is a clever idea that is likely to end up disappointing. Having said that, go for it! What is there to lose by trying?

It's OK to vent vertically up to the attic, as long as you are (as you plan to be) carrying on and venting to the outside. To determine whether your total length of vent and number of 90 degree turns is OK, you'll need to consult your dryer's owner's manual for the data. (Sounds OK to me, but I'm not familiar with your specs.) But one thing to consider, the horizontal run shouldn't be horizontal, but at as much of slant as you can manage from where it emerges from the attic floor to the point it exits the house. This will ease the constriction of the 90 degree bend as much as possible. You can buy in-line boost fans (I think Fan-tech is one manufacturer), but you may not need one. Always use rigid metal piping, not the plastic or metal corrugated stuff. And I prefer to plan on an easy dissassembly point(s), or a clean-out. Make it very easy to sweep the pipe - a couple of times per year is not too often. Cleaning regularly will save you money, decrease dryer time and protect against dryer fires caused by lint in the pipe. Depending on your typical local storm patterns, you may need to protect the opening with louvers or a hood to avoid having water or snow enter the pipe. But altogether it doesn't sound like a difficult project. Molly~

Thanks sparky. I had not heard of the Robita Dryer Vent. Seems like another good solution to allow the dryer to be pushed closer to the wall. Good find. I am intrigued by this one way flap that fits behind the dryer. Is it a separate damper like I have linked below? The standard design of a dryer vent seems to be based on the idea that when hot air is blowing out no brave mouse would want to crawl against the warm air flow. I hope there is no such Olympic mouse (or bird) that can do that. Is the separate damper I have linked below what you are referring to Sparky? Most hood styles would have another sort of damper (or one way flap/flaps) at the exterior of the house. Are you suggesting a second damper inside the house for extra mouse protection? Separate damper for added critter protection?

Who cares what the builder thinks. This is a TERRIBLE Install and a very poor choice of venting location. It would violate code here. Any roof vent of hot emissions (furnace, dryer, etc.) that is through a roof must be at least four feet above the roof line AND four feet away from any portion of the roof that is the same height or higher. A proper vent cap should be used such as this: Or this: What is on there now looks like a standard roof vent. That is designed for passive venting of the attic space, not a forced air exhaust like a dryer. The problem now is that they cut the vent pipe very short so a proper vent cap may not fit. A dryer vent should have no screen (they catch lint). It should have a self closing flap or hinged door that opens when the dryer blower comes on. When the dryer shuts off it should fully close to keep critters, insects and the elements (rain, etc) out of the vent pipe. You will also also need to crawl up on the roof at least once or twice per year and check for clogged lint. You will also need to look in the attic several times per year to make sure the vent pipe has not come loose. If they wont fix it I would find a Building inspector and ask if that is code. I highly doubt it. Where is the dryer located? If it is in a closet or a small room then it may not have enough makeup air for what it is tying to push out the vent. If it is in a closet, leave the door open. If it is in a small room leave the door open or open a window in the room if it has one. If this prices the drying time then you need to supply more makeup air to the location where the dryer is installed. You would do better with a condenser or heat pump dryer that is ventless than that setup. Here is a Charleston home inspector who discusses this very topic: http://www.summerville-home-inspector.com/content/charleston-home-inspector-discusses-dryer-vents