Is it okay to have a dryer vent in the wall cavity?
One of the leading causes of house fires is dirty or plugged clothes dryer vents. Dryer vents should not be installed in ways that make them difficult to clean and inspect.  Any vent in a wall cavity should be made of solid metal, with all joints sealed with metallic tape. There should not be any tight turns and they also need to be sized properly to the distance run. Flexible or corrugated plastic ducts should never be used in enclosed areas. When possible, it is safer to have vents exposed, as short as possible, made with metal duct with a minimum of bends. Ducts should be inspected for excess lint and vermin debris regularly and cleaned on regular intervals, usually every 6 months or annually depending on your usage. Also, anytime you see that your dryer is taking longer than usual to complete a drying cycle, it is a good idea to check the venting for problems.