Return to the Basements Forum | Post a Follow-Up

To insulate or not to insulate a basement bathroom??

Posted by mrmichaeljmoore (My Page) on
Mon, Mar 29, 10 at 14:23

I am in the process of doing a basement bathroom.
It will be connected to an already existing finished basement.

I have a question regarding what to do for insulation for the bathroom wall on the poured foundation wall. The wall is completely below grade. The sink and toilet will be on the foundation wall. Shower is completely interior. And the pex warer supply pipes that are on that wall are near the bottom third of the concrete wall.

Originally, I was going to do fiberglass batts in the stud wall cavities.
Then I did a little research on this topic and found a better way to go is the rigid foam board insulation.....

Unfortunately, though, I have no way of doing the rigid foam insulation. The stud walls are already up, and are completely fire blocked. So, I cant even slide the 1/2" Dow Styrofoam behind the studs....

For what it is worth, the bathroom will have radiant floor heat (Warm Up brand) and a Panasonic Whisper Warm 110 CFM vent the bathroom will be heated and vented sufficiently, I would assume to remove any dampness....

Plus, I always run dehumidifiers on both the unfinished and finished parts of the basement in the summer. And my pellet stove is always running in the finished basement in the winter. So the basement is usually around 40-55% humidity.

Also, I have never got any water through the poured foundation wall that will now be part of the bathroom (knocking on wood right now). Also, one of the previous homeowners put a coat of what appears to be Dry Lock on the wall as well.

So, this is my question....
Should I just put some batts in the stud cavities? Or should I just leave it uninsulated?
If I do fiberglass batts, should I do faced batts toward the warm in winter side? Or unfaced batts?


Follow-Up Postings:

RE: To insulate or not to insulate a basement bathroom??

If there's space between the studs and the foundation wall, you can still slip in extruded polystyrene (XPS)--cut into long strips, push to the wall then slide it along. If that's not feasible, place the XPS tightly between the studs. Two inches will give you R10. No batts.

RE: To insulate or not to insulate a basement bathroom??

worthy --
thanks for replying...

unfortunately, I can not slide in the XPS behind the studs. By local code, we had to install fire blocking on the end of the wall. So now it is closed off.

And, I can't install XPS in between the studs becuase I already have electrical and piping running through the studs.

The gap between the wall and the stud is only a little more than 1/2". So even if I could slide in the XPS behind the studs, I would only get about r 3 value....

Thats why I figured it is almost better to put no insulation. The pipes arent gonna freeze;
Plus, if I do get moisture back there, then there will be no fiberglass insulation to get wet. With no insulation, the wall will just dry out. (with the help of my dehumidifers and the bathroom vent fan, of course)

If I get a chance, I will post a picture tonight of the studded wall with the roughed-in plumbing and electrical.

thanks again.

I'll try to post a picture later....

RE: To insulate or not to insulate a basement bathroom??

Thanks to everyone for ther help thus far..
still researching.

I found this at Lowes:

I can staple it right to the studs, which would leave an air pocket between concrete wall and studs, then go over it with sheetrock.

Anybody have an opinion on that product? Anybody forsee any problems with it?

RE: To insulate or not to insulate a basement bathroom??

The US Department of Energy says reflective insulation should not be used in cold or very cold climates. Besides, it's designed for attic installation in reflecting heat outward where it's used as a radiant barrier. Foil used as a vapor barrier on a basement wall will likely trap moisture behind the wall and feed mould. (See BSI-037.) (Mould can grow on a concrete wall, not just wood.)

I would simply fit in XPS as tightly as you can and seal with building tape or foam around the pipes and wiring. (FG and Membrain vapour retarder would work too. But you have too little a space to justify buying a roll of Membrain.)

RE: To insulate or not to insulate a basement bathroom??

thanks again for replying, worthy...

But whats amazing to me is that there are so many differing opinions (on this forum and other forums that I have asked the same exact question)....frustrating for a homeowner.
Yes vapor barrier, no vapor barrier.
Faced insulation, unfaced insulation..

I am wondering though...... would the safest option to be leave it uninsulated??
That way if I do get any moisture, it can dry out on its own and I wont have to worry about any insulation retaining moisture
Pipes will not thats not an issue.

Like I said, the bathroom will have radiant floor heating and a Panasonic 110CFM vent fan (with the heater)....
Plus, I always have two dehumidifiers running in the basement.along with my pellet stove in the winter.
So the bathroom shouldnt be damp

Unless someone can give me an overwhelming reason why I shouldnt leave it uninsulated, I may go that route

Thanks again.

RE: To insulate or not to insulate a basement bathroom??

whats amazing to me is that there are so many differing opinions

Dirty Harry understood the phenomena! But his comment isn't family friendly.

That's why on technical matters I buttress my statements with authority.

Until the 1960's, insulation was virtually non-existent. Energy was cheap, so North Americans just piled on more as needed to keep up with the air exchanges in their leaky uninsulated homes. No damage other than to your pocketbook.

RE: To insulate or not to insulate a basement bathroom??

Here are a few pics of what my wall looks like now.

The gap between the back of the studs and the concrete wall is no more than 3/4".
Plus, it is all blocked off and fire foamed, so I cant slide some 1/2" rigid foam behind it.
Plus, as you can see, I have all the plumbing and wiring running through the studsso not much room in the stud cavity.

Like I said, I think I may go the no insulation route...

thanks for the help.





RE: To insulate or not to insulate a basement bathroom??

The most important part of the basement wall to insulate and seal is the first three-four feet from the top. Particularly the rim joist area.

Fiberglass stuffed between the joists at the rim is useless as an air barrier; and when it gets wet, it encourages mould growth. In Minnesota, fg in the rims is forbidden in some builder insurance policies. Instead, cut XPS to size, stuff in and seal with foam or caulk if possible.

RE: To insulate or not to insulate a basement bathroom??

I would put up that foam 2" panels in between the studs, but I see a bigger problem. The plates studding are regular pine. With wood resting on a cement floor, there's a chance of moisture rotting those studs. I don't think you have anything to worry about as most people and contractors do that. I learn this only by someone whom told me about it when they had a two million dollar church put up and he worked with the builder.

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Basements Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here