Not really sure where to post this one, but here goes. I live in the SF Bay Area, and have recently renovated my laundry room on an older home. I moved my dryer from an exterior wall, to an interior wall. Presently, I'm using 4" flex duct to exhaust the dryer. I want to install ducting in the wall, out through the floor, (I'm on a foundation), and out an exterior wall. Is this allowed? I've seen numerous threads about ducting up through the roof. Also, do I, or don't I need B2 vent pipe, or will regular aluminum ducting be ok? (I don't need to have insulation around the duct).

 

Check with your local codes, since you live on the left coast, but generally you can run the ductwork through the floor, but when it goes horizontal the duct must be rigid. This is to prevent sagging and collection of moisture and combustible materials. If you have access to the wall you may want to entertain installing one of the flat transition dryer periscope type vents. They are round on each end, extend like a periscope and have a flat 3 1/2" body that will fit between a 2x wall cavity.