While not ideal, I did put my shower niches in the exterior wall, as the closest interior wall hosts my showerhead, diverter, thermostatic mixer and handheld-shower wall outlet (i.e., too much going on on that wall) and the second interior wall is at the other end of my shower 68" away. I considered getting a preformed Noble shower niche made from polystyrene to at least keep some insulation value in the wall, but I think the R value of a Noble niche is all of 2 or 3, so it was not enough of an incentive given that none of Noble's design-size combos appealed to me. Back in January I had Massave perform a free energy audit of my remodeled home. I specifically asked the tech his opinion about my placement of the shower niche in the exterior wall and he dismissed my concerns over the loss of insulation there, stating that it was minimal in the scheme of things (whether he meant relative to the bathroom or to the whole house, I don't know). My master bath is still unfinished so I have yet to use the shower. While the niche itself was definitely cold during these past winter months (I'm in MA), the rest of my bathroom was fairly warm -- even without the kickspace heater in place yet (but receiving spillover heat from the adjacent, heated closet) -- so I'm okay with my trade-off.

There initially was a comment before mine dated May 26, 2017 which was deleted. It does look silly without it still being there. Many pros look at the date prior to opening a thread. There is a current thread in the pro to pro section on this very topic due to some recent Houzz format changes. By using an old thread you are short changing yourself on available advise. Also due to the rapid advances in technology and products available now many responses given 5 years ago will not be the same as the ones provided to you today. Not to say there is not valuable information in older threads. That's why I bring it up and why you should care. There is your 2017 answer:)

My feeling about shelves (or anything) protruding or projecting from tub or shower walls, is to avoid them. I am a total klutz, and have been known to whack my elbow(s) on the recessed niche/shelf in my own bathroom (while reaching to take something from the niche, or, while putting something back. Having something projecting outward is just asking for an "ouch!" for a klutz like me. I've seen some beautiful, sill-like shelves in niches, but as flush as possible would still be my preference.

love the message niche idea...now I want one too... I am one of those "use every inch" types so I think putting stuff in between studs is great--otherwise think of all the wasted space!! If you don't fry, etc. maybe it isn't a concern, but I just wanted to say I have a narrow shelf behind my cooktop now, pretty high up, with a few doodads and jars on it, and it is DISGUSTING. I reached for something the other day and it had the nastiest film on it. TO clean it I would have to dump out all the spices in the bottle and wash it. So I just put it back, LOL...anyway, even if there's not grease there will be steam, which will attract dust and make a film. So if you do want a niche plan on it being purely decorative, and on washing the stuf in it periodically. BTW what is OOAK?