To insulate or not to insulate a basement bathroom??

[mrmichaeljmoore]

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 can’t 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 fan....so 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?


thanks.
mm

[mrmichaeljmoore]

still researching….

I found this at Lowes:

http://www.reflectixinc.com/basepage...&pageIndex=562

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?

[cacher_chick]

Do not use a vapor barrier below grade as it will trap the water vapor coming from the ground and cause future problems.

This product would be fine on the wall for the part that is above grade, as the water vapor will transfer outward. Once below grade, the water vapor can only transfer inward.

[mrmichaeljmoore]

Thanks for replying, cacher_chick....

But what’s 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 freeze….so that’s 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 shouldn’t be damp…

Unless someone can give me an overwhelming reason why I shouldn’t leave it uninsulated, I may go that route…

Thanks again.
mm

[Dana]

Vapor retarders have no place in a basement- foundation walls need to be able to dry toward the interior. NEVER use just a studwall & batts against a foundation wall or ground moisture will rot the cold side of the studs. It might be 45-50% relative humidity in the heated interior of the basement, but the dew point of 45%RH 70F air is above 50F, and the cold side of the studs will likely get well below that. But if you put in a vapor retarder on the interior side, ground moisture will be trapped in the studwall to raise the relative humidity well into the mold-growth zone. If you put a vapor retarder between the foundation and studs, the foundation saturates, water is driven higher to dry toward the exterior on the above grade portion to effloresce & spall, or even into the foundation sill to create rot conditions therer.

This isn't just an opinion- it's the physics of water, and the biology of mold.

It's best to use semi-vapor-permeable foam insulation against the foundation, and finish out the R with UNfaced batts in a studwall, as long as you can keep the wintertime average temp of cold edge of the stud well above 50F. It's often less work to just use thicker foam (up to 2" /R10 for XPS, or 4"/R16 for EPS beadboard.) Be sure to avoid product with foil or poly facers, since they are both highly vapor-retardent. See: http://www.buildingscience.com/documents/information-sheets/5-thermal-control/basement-insulation/ As long as the foam insulation can pass water vapor at some minimal level the assembly can dry. Pink/blue XPS becomes semi-IMpermeable at thicknesses over 2", making it harder for the foundation to dry toward the warm interior. With beadboard or fiber-faced polyisocyanurate (sold as roofing insulation in commercial space) you can go much higher in total R-value.

For much of the US an inch of XPS and a 2x3" studwall with R8 unfaced batts is the cheapest way to go, for a nominal R13 total. For extra-cold areas, 2" of XPS and a 2x4" studwall with unfaced R13-R15 batts gives you a result over R20.

[edited to add...] ... so bottom line, from a mold-potential point of view you're kind of stuck if the studs are already in. If there's enough space to slip in some 6-mil polyethylene between just the stud-edges and the foundation with an inch or so exposed on either side of the stud, leaving the rest of the stud-bay without a vapor retarder, you could spray ~2" of closed cell foam in there for ~R10-R12. If it's a small amount of area the DIY kits from Fomo-Foam, TigerFoam, Dow Frothpak etc. are about perfect. IF there's at least 1/4" of gap between the stud & foundation everywhere you could use the foam itself to be the vapor-retarder to limit ground moisture from wicking/condensing into the cold edge studs. But if the studs are tight up against the concrete, forget about it. Be sure to use vapor-permeable interior finishes (no vinyl or foil wall papers, just latex) and keep the RH in the bathroom under 50% with it's own dehumidifier.

[mrmichaeljmoore]

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 can’t slide some 1/2” rigid foam behind it.
Plus, as you can see, I have all the plumbing and wiring running through the studs…so not much room in the stud cavity.

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

thanks for the help….
mm

[mrmichaeljmoore]

Do not use a vapor barrier below grade as it will trap the water vapor coming from the ground and cause future problems.

This product would be fine on the wall for the part that is above grade, as the water vapor will transfer outward. Once below grade, the water vapor can only transfer inward.

well....the whole wall is below grade, so the Refelctinx stuff wont work.