Correct way to insulate this situation in bathroom

jasesun23 · 05-03-2012, 08:46 AM

My bathroom faces the back of my house. Its on the second floor and they way the house was built the first floor has eaves. Pics attached. With the bathroom gutted I have access to the eaves. I removed old insulation in the floor and the walls. How should this Eave (believe thats what it is called be insulated). From what I can tell there is no venting in the eaves. No soffit vents. Hopefully the pics will give a better idea.
Pic1 - Outside of house to understand what I mean by eaves
Pic2 - bathroom wall facing exterior of house
Pic3 - shows old fiberglass insulation stuffed in the corners
Pic4- shows one slot/corner I removed the insulation from
Pic5- Eave insulation going down the length of the house

jasesun23 · 05-03-2012, 09:03 AM

After correctly insulating the eaves I was wondering if I could insulate the walls this way. Could I cut some .5" polyiso foam to put up on the walls. Than add R13 fiberglass insulation on top of that (the kraft paper kind). I like the idea of the rigid foam to prevent air drafts? I'm concerned that the polyiso is a vapor barrier and the kraft fiberglass insulation is also one.

pucks101 · 05-03-2012, 09:20 AM

It looks like they insulated that space completely from the exterior, as if it was all interior space. If so, no need for soffit vents, because it's all considered heated space, but I'm not sure it was done completely / correctly.

I'm kind of confused about the vapor barriers facing each other. I would think the barrier should all be the same way, helping create a warm / dry zone, but it looks like the walls have paper facing the exterior (incorrect?), and the floor of the soffit has barrier facing interior (correct?). I would consider that little roof area to be a continuation of wall and insulate that, to create one, contiguous insulated exterior "wall".

joecaption · 05-03-2012, 11:02 AM

It looks to me like the vaper barrier on the insulation is installed all up side down.
That area should not have been treated as a heated area.
When I've been doing knee walls I install the insulation with the vaper barrier toward the condition wall (toward the sheetrock) and add Tyvek on the back side to act as a wind break, but since you have no venting in that area not even that is needed.
Another way would be to use 1' blue foam over the studs in the room and install the sheetrock over that with insulation with no vaper barrier on the back side of the wall.
The insulation over the ceiling is upside down.

jasesun23 · 05-04-2012, 01:02 PM

Okay I'm following a little bit but maybe each arrow in this picture can be explained. Also I can only work with this space, I'm not going to rip out the walls to do the whole eave.

A- Is is correct to have no insulation on the roof of the eaves. There is nothing there now.

B- is it correct to stuff the insulation kraft side facing inside of house in the corner where the roof eave meets the floor and then down along the floor /soffit of eave.

C- looking down the eave to the next room it shows the kraft fiberglass insulation facing the outside of the house. This is strange as the walls of the bathroom the kraft paper faced the inside of the house towards the drywall.

D- is the floor joist going into the bathroom and I'm sure accross the whole house. There used to be insulation all the way across the floors. I removed it and didn't think it was needed. However the floor joist have no blockage from the area in the eaves to the bathroom. Its just a continual space. Not sure I'm explaining this well.

Anyway what is the best way to proceed. Even if I put some rigid foam between the studs and the drywall the spaces inbetween the floor joists will be there bring any cold air from the eves into the bathroom floor?

Also there is a bathroom right below this. The insulation in the second floor bathroom had the kraft paper facing up in the floor. Which means in the 1st floor bathroom the non kraft side was facing the ceiling. That is incorrect. Also the FG insulation in the floor was only 3.5 inches while the joists are 2x10s.

pucks101 · 05-04-2012, 06:29 PM

I'm basically suggesting you treat from point of contact of C/A, down length of A, length of B, and across to point of contact of B/D as one outside wall and insulate really well (thickest batting you can fit), paper-side in; then treat wall C as if it were an interior wall, like between 2 bedrooms. You can leave open, or insulate with batting with no paper. The paper is a vapor barrier, and you don't want two vapor barriers locking moisture into a dead wall space.