How do I Prep/Insulate Stud Walls For Moisture Protections (exter

enduringApril 21, 2013


I am now on to my 2nd bathroom. I didn't ask this insulation question at the time of the first bathroom remodel so I don't really know how to do this. I just assumed I knew on the first job.

I have an exterior wall that will need insulation. Then the wall covering. I plan to have a vanity and toilet up against this exterior wall. I may or may not tile a wainscot in the open areas of the wall. Other wise the walls will be painted, and cabinets, vanity and toilet installed. The plumbing will come up from the floor and not in the wall.

I will have an exhaust fan in the room vented through the roof.

I will have a shower and washer and dryer along an interior wall that is also torn down to the studs. The other side of the wall is lathe and plaster, plaster keys visible in the wall space.

There was some mold growing on the dry wall that was placed over the original plaster in the room. the mold was probably a result of moisture leaking around the drop in sink, and the shower surround. Everything is now out, down to the studs. The studs will be looked over by my carpenter. I will not be doing the structural repairs, he will do what needs doing.

What I see looking at the sheathing of this old house is silver dollar sized holes at every stud, on the outside black material. I do know that there is 12" siding of a pressed material and painted on the exterior. I had thought that the old lab narrow siding was still under all, but this appears to not be the case as the holes are indication to me that insulation was blown in after it was built. I am thinking that the old lap siding was removed in the 70's and it was resided after insulation blown in. I will see DML later today and will ask her if she remembers this part of the remodel from the 70's.

Then 5 years ago my DML put up Sears vinyl siding over the 12" pressed board siding. There was a layer of closed or open cell insulation that they installed under the vinyl.

1) Do I just get the paper backed insulation and staple it in place with the paper facing into the room?

2) If this exterior wall would have a shower against it, how would I do the insulation, the same?

3) Is the siding layers an issue in the insulation/moisture protection strategy?

4) I would like to treat the wall with the wash/dryer to help with sound deadening, as this wall is shared with the living room where the TV is located. How can this be done?

5) Do I insulate the interior walls too? There will be some pocket doors so those wont have insulation needs.

I have to run, but I can post a plan view and some elevations of my project this early afternoon if that is helpful.

This post was edited by enduring on Sun, Apr 21, 13 at 10:54

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Sophie Wheeler

Your location in the country has the primary bearing on what side any moisture barrier faces. It goes to the warm side, so if you are in a primarily AC climate, it goes to the outside, if a heating climate, to the interior. That is because moisture condenses when faced with cooler air, much like a can of coke pulled out of the fridge. You don't want that happening behind your walls.

Your location also determines how much insulation is required by code. If you are agricultural zone 5 or lower, then putting plumbing on an outside wall is not advisable if that is only a 2x4 wall unless you can access the exterior to apply a couple of inches of rigid foam insulation.

Here is a link that might be useful: Michigan State Energy Saving Tips

    Bookmark   April 21, 2013 at 5:24PM
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Thanks Hollysprings, for the map and information. I did a search after I started this thread and found a thread that almost matched my questions from about 5 or so years ago. Weedy, I think was the member, linked to the building science site, or some name like that at that time. I found, as you said, I would need paper to the inside of the stud space, next to the interior wall. I am glad for that as that is how I did my kitchen and my other bathroom. I just thought that was convention. And I guess it is around here. But I hear so much talk of vapor management it concerned me. I still am wondering about the styrofoam like lining, that is underneath the vinyl siding. Do you think that this is causing a vapor trap within the walls? I don't see any evidence of an issue at this time, but just wondering if this will be a problem in the long run.

Anyone, I still would like feedback on questions 2,3,4,&5. But these are not as critical as #1, I believe.

    Bookmark   April 21, 2013 at 7:35PM
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1) As pointed out above, to get accurate answers you have to state your exact climate zone.

2) No difference in the required insulation. If this is a tiled shower, as opposed to a freestanding unit, though, you have to provide a completely waterproof backing, such as cement board or a waterproof membrane, such as Kerdi over standard drywall meticulously installed.

3) Drilling holes to add insulation and not patching is a recipe for future bigger costs. I once bought an old home that had been so "improved"; eventually the waterlogged ceiling caved in. Hopefully, the added layers of siding provide enough protection from bulk (liquid) water.

4) Four standard ways: add a layer of dampened drywall, such as Quietrock; sound isolation clips; Green Glue and standard drywall; resilient channels and another layer of drywall. None of these methods will do anything for "flanking" sounds, coming under and around the wall, so don't expect a tremendous improvement. And if this is a DIY job, forget the resilient channels.

5) Insulation will yield an imperceptible decrease in sound transmission, so why bother.

This post was edited by worthy on Mon, Apr 22, 13 at 18:46

    Bookmark   April 22, 2013 at 2:31PM
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Thanks Worthy for your help. It may have been you who linked the site with the map. Yes it was you, I just looked in my history for the post, and it was only 6 months ago. I read it and found it helpful, but at times over my head. Something that definitely takes a few readings.

I live in the bottom of zone 6, central Iowa. So I will use the insulation with the paper facing into the room. I'll ask the carpenter about the old insulation holes, there were no leaks there though.

My shower walls will be tiled over Hydroban over cement board. I will be using a Kohler cast iron shower pan. I have plans to tile the ceiling too but I am apprehensive because of the anticipated level of difficulty with that and the grouting.

I might skip the sound deadening strategies. Unless the carpenter knows about the options.

I have a carpenter that will build my walls and drywall, with cement board in the shower. I have an electrician that will do the wiring, and a plumber to move all my plumbing. I am functioning as the GC and designer of the space. I will be doing the tiling.

You may remember my other bathroom project, with what someone stated had the most over thought floor in a long time. I was trying to reenforce the joist for stone tile. You helped I believe. It turned out well and it gets a lot of complements for style.

    Bookmark   April 22, 2013 at 7:41PM
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Hello, I'm back ready to finalize what I am going to do with the exterior wall insulation of my south facing bathroom wall in Iowa. Central Iowa is zone 5 on the map above that Hollysprings posted. On another thread Worthy had a link to the building science site and I found another paper written that addresses vapor barriers. I linked it below.

I will have a shower and washer/dryer in this room. I will have a 170cfm Fantech exhaust fan in the room with remote fan in the attic and 2 vents, one at the shower and the other at the W/D stack.


2x4 stud wall that faces the south. There is one window in this wall. I will have drywall and latex paint on the interior finished wall.

The material that is on the exterior side of the studs is 1x8 T&G boards from the 20's when the house was built. Out side of the boards is an old siding of pressed composite material that is from the 70's. It looks like the original narrow wood siding was removed at that time. The last exterior layer was put on by Sears (over the 70's era siding) within the last 10 years. It is a vinyl siding with a 3/4 pink extruded polystyrene insulation under the vinyl. The polystyrene material is by Owens Corning and says "Weatherb...Exterior Protecti..." (I only have a small section of material to read).

I have been planning on using Roxul batt insulation. This requires a poly 6 mil vapor barrier sheet put on the inside surface of this wall. Then the stabled areas get covered with "Tuck Tape". Of course I can't find Tuck Tape in the US.

1) Will it be appropriate to put this vapor barrier on the interior surface of my studs with all the sheathing materials that are on the outside studs? Or will I be creating a vapor sandwich, causing damage to the studs?
2) Will Tyvek Tape substitue for Tuck Tape?
3) If not Tyvek Tape, what does substitute for Tuck Tape?

Here is a link that might be useful: BSD-106: Understanding Vapor Barriers

    Bookmark   July 19, 2013 at 6:58PM
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