A couple considerations: Access from an attic is necessary to avoid ripping up drywall. You will need to be able to get to the area you want the vent to exit. eg a big ladder if it is on the side or some way to get on the roof. If you want to control the fan with a separate switch, you'll need to run some new electrical lines for that. Unless your hubby just loves DIY, this is going to be a bit of a project. It's not overly complicated, but working in attics, climbing ladders and fishing electrical lines aren't really most people's idea of a fun weekend - especially if you don't really care about the result.

Patricia and GN Builders, thank you both for such quick responses. Patricia - the bedroom does have an egress window, facing South, the bathroom fan would be facing East and yes run directly under the Deck. Great point on ventilation... I may just be overthinking this. GN Builders - Coming through the rim-joist and the deck ledger is my current and only plan indeed. Any specific Vent Caps you may recommend? I was looking for a metal one with a grate to protect from any potential "intruders". Thanks again!

Short answer: 110cfm is fine, 70cfm was not technically undersized. Long answer: If your U.S. local building code has not amended IRC M1505 or IMC403, then only a 50cfm (switchable) exhaust fan is required no matter the square footage. The ventilation is associated with fresh air to an enclosed toilet room or entire bathroom, and can be provided via a window rather than exhaust fan. It is not to remove heat. As an alternative, you can have as little as a 20cfm continuous fan when the room is occupied. However, a practical matter is to use the exhaust for steam/humidity. Home Ventilating Institute (HVI) issues guidelines as follows: So those are the requirements vs guidelines for you to follow. When deciding, factor in: - Distance of fan from each plumbing fixture, single or multiple fans - Height of ceiling, e.g. if vaulted - Sones on higher cfm units. Some prefer louder to drown out human noises, some don't want to hear a fan. - remote fan in attic vs room ceiling

The fan you selected has a built-in back draft damper. You should not have to install a special vent cap. A 4 inch wall vent with a damper should work well. As tempting as it is, I would not join the duct work with a wye. I think it is going to cause problems. I am not familiar with the Delta fans. Are they made by Panasonic? None of my fans have a humidity sensor. I installed an electronic timer switches. I start the shower and the timer at the same time. Both fans are inside the shower stall. It has worked well for the past 10 years.