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The Importance of Bath Ventilation – a Lesson Re-Learned in my Master Bath


A few years back we did our master bath. Well, to be more accurate – we put a quote, unquote master bath into what was once an 8×8 closet. After a lot of consideration, we decided not to reconfigure the room, I mean – move walls or change the door’s location. We just put it in.

We decided to hire this job out to my wife’s Other Man, you know – the “Other Man” … Mr. Pete, we’ll call him. He works with my wife as her partner on her flip projects. (Note: Number 3 is under way, but is moving slowly – thanks in part to an extremely uncooperative Winter.) Here’s a look at their last >> Mrs. Moxie Flips Out 2.

You may remember me mentioning “our master bath project” in the post >> Before & After? idk … Around Here It Seems Like a Perpetual State of During.  Yep, those two pics above were about all the coverage I could muster on it – one, I really didn’t have the time to feature it, and two, well, I really didn’t do much work for it. This was Jen’s project (thank you Jen). And right around the New Year, 2011 – she pushed it through.

Not going too much more into it, I knew at the time of one area where we (*cough* the Other Man) skimped. For the connection on, the venting for, the new bath fan, he used flex duct, and dropped it into a corner of our attic. There it funneled into a strange apparatus that he … engineered.

Now, I knew, you should almost under no circumstance ever vent into an attic (not even into a vented soffit – like some builders are prone to do). I knew this … yet I did defer (for a couple reasons) to my wife’s partner; I let him have his way.

So … What happened?

Well, within a matter of months, we began to notice the formation of small spots on the bathroom ceiling. Yep, Mold!

While this was quickly wiped clean, I also made a quick visit to the attic, where I noticed that the … apparatus had come disconnected from the bath fan housing. (Essentially the bath fan blew it right off.)  At the time, I remember thinking – “I have got to address that bath fan venting, and get it vented properly, to the outside.”

That was probably somewhere around, January 2012. Ha!

And well, another year … and a half passed and in that time the mold spots returned and left, and then returned, this time – a little more pronounced. Areas of the ceiling too showed signs of puckering and the paint even began to flake and peel in some spots. Whoa! I can remember at the time saying, “Yes, I know Dear. I’m getting to it.”

Installing Bath Fan Venting in a Finished Attic Space

I hope through my story I impress upon you the importance of proper bath ventilation. And yes, sure, your bath venting set-up can break down at many places. Mine – sure, insufficient venting, which was dumping moist air into an under-insulated attic above a ceiling constructed of plaster and lath.

Now, I know those may not have been the only factors coming into play here. The bath door, for example – did the installer (me) ensure that a minimum ¾ inch clearance was left to allow for the proper amount of make-up air? Yeah, you know – an old house and the floor at the door is slightly slanted, so just to be sure – I took another 3/8” off of it before I even started the work.

Ensure a 3/4″ space for bath fan make up air

And anyway … I took a Sunday afternoon, and as our attic is a finish…able space, I hard-piped using 4” rigid duct, going out the attic’s side wall. It wasn’t a super-amazing or difficult project, considering of course that the bath fan had already been installed. But imagine it – a one man show up into the 3rd-floor attic, down to the ground and then up a 32’ ladder. Down the 32’ foot ladder and repeat until it is hooked up. A five-foot run of duct took roughly four hours (ugh!) and I see why now that the Other Man wanted to avoid it.

Other measures taken: Prior to touch up the service with some drywall compound, I used an over-the-counter moldicide (maybe I can call it that) to more permanently treat the ceiling, I primed with KILZ 2 and I painted using a Behr Kitchen and Bath paint. This Sateen finish – hopefully offering a more moisture-resistant sheen. (Like the Other Man who painted with a Flat … I simply grabbed what I had lying around.)  I added a Mildewcide Paint Additive before rolling it on.

And one final note: When choosing our bath fan, I selected a NuToneModel 684NT. It’s very much a budget model, sold exclusively at the Home Depot. Rated at 80cfm and up to 75sf, I figured it was enough to service this just smaller than 8×8, less than 64sf, space. (I chose the same model for our 5 x 12 hall bath, and installed it independent of this renovation (with proper venting) several years earlier.)

If the mold and paint flaking in the end does not subside, I plan to upgrade this fan – a process which will unfortunately require an entirely new housing i.e. I can’t just slip in a new, beefier fan motor. Also, as I seem to constantly remind everyone in my household, there is one very important thing when it comes to bath ventilation – you have to, regardless of the sizing of your bath fan, actually run it when you shower. Thank you.


In the process of sanding off needed repairs I made a quick-tip vid on Minimizing Dust when Sanding Drywall Repairs.



Disclaimer: This post was sponsored by no one, other than myself. While I am again humbled by a house, I share it to show what could happen if you don’t do things right the first time. I know too that I need work on not only my attic insulation (possibly insulating my new duct also), the paint in my gables, as well as also, Yes I know – I still need to stain my bathroom door. I swear I’m getting to it.

For more on Installing a Rigid Bath Fan Duct in 9 Steps, here. For more Mold Prevention Tips, please see the article – Building for the Fungus Among Us.  :~)

For more on selecting a Bath Fan and how to vent it, here’s an article from HGTV – Choosing a Bath Ventilation Fan~ jb



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