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Old 12-29-2018, 10:50 AM   #61
Topspin
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OK already having said that, from the rest of the pros, why is it that when we put vapor barrier backed insulation on a stud wall prior to putting up a waterproof membrane shower, it is recommended to slit the paper to allow vapor transmission so we donít have two moisture barriers in the wall? If thatís the case with a simple paper backing creating a separate vapor barrier, what about non-breathable foam insulation surrounded by spray can foam that guarantees thereís no vapor transmission? Sounds good for temperature maintenance, but what about that double vapor barrier issue?
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Old 12-29-2018, 11:02 AM   #62
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XPS is considered a vapor retarder and not a vapor barrier. IIRC it will allow vapor to pass without being subject to temperature swings that would lead to condensation.

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Old 12-29-2018, 11:04 AM   #63
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Notching for the nail guards is a good idea, I'll go ahead and do that with the oscillating tool later this evening when I install the 12x28 kerdi niche on the back 1/2 wall.

The shut offs can be accessed from the back wall. The master bedroom is located directly behind and I can always cut the drywall out for valve/fitting replacement. I don't mind patching up drywall haha.

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Old 12-29-2018, 11:07 AM   #64
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Kevin, you raise a good point. Usually, foam is a vapor retarder, not a barrier. Houses that are fully foam insulated work usually fine. I know this to be true of polyiso foam for sure. Ali used XPS panels which are also commonly used in new construction, more often though as a sheathing to reduce thermal bridging from the outside. Having said that, you refer to that film on top of the XPS panel, and that certainly would be more of a vapor barrier. One can pull it off, actually.

However, as long as the wall cavity doesn't suffer from infiltration which could bring moisture into it, especially during the cold season, I don't think the double barrier (vapor retarder on one side/moisture barrier on the other side) would present a problem. Only if water or vapor would consistently make it into that space could it be a problem.

Now, with fiberglass batts, there is always air circulation since it's not an airtight type of insulation unless the cavity has been flashed with spray foam before). That's why slitting the Kraft paper backing is important to avoid moisture buildup. I think the more extreme the climate is in which you live, the more important this is.

Having said this, I've treated multiple rooms in my 1968 ranch with "poor man's sprayfoam" (what Ali did). The energy savings and especially the comfort are awesome, especially in a ceramic shower during the dead of winter.
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Old 12-29-2018, 12:32 PM   #65
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XPS is considered a vapor retarder and not a vapor barrier. IIRC it will allow vapor to pass without being subject to temperature swings that would lead to condensation.
Depends upon what you consider a barrier, Ali. For many years the construction industry considered anything with a perm rating lower than 1.0 to be a vapor barrier. Some of us older members still do.

These days it depends upon whom you ask. There is definitely a move toward calling anything above 0.1 perms a vapor retarder, but the effects are still the same.

As to your XPS being a retarder and not a barrier, that would depend upon the quality and thickness. Some of that extruded foam is pretty dense and you can get below 1 perm with less than an inch.

As for temperature "swings" resulting in condensation, that would depend entirely upon whether the temperature reached the dew point of the ambient air. The temperature can swing all it wants without any water vapor condensing if the temperature hasn't reached the dew point.

Having something like gypsum drywall sandwiched between a serious retarder such as the Kraft paper used as backing for fiberglass insulation and an even more serious retarder such as Kerdi, especially in a shower against an outside wall where the vapor pressure from inside will be very high at times, especially when the exterior is very cold, is a bad idea. The use of an effective air barrier on the exterior of the wall is necessary in such applications, but removing or at least substantially defeating the Kraft barrier is essential.

The same situation with a CBU in place of the gypsum drywall? The CBU is not subject to deterioration as would be the drywall, but the conditions remain the same and the accumulation of moisture in the CBU will be a real consideration. Will it be harmful? I dunno, but there is never the same incentive for the moisture to leave the CBU as there was for it to enter and I don't think twenty or thirty years of that accumulation can be a positive thing.

Trying to create a perfect seal in the middle of such wall structures by using solid foam or/and spray foam insulation materials I've just never thought was a good approach. But the arguments about building science in that arena have been going on longer than I've been involved and will likely go on a lot longer. Some methods are gonna work better than others and if you like what you're doing, be happy, don't worry.

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Old 12-29-2018, 01:50 PM   #66
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Wolfgang, I read through your shower thread this morning, turned out great man. I too get enjoyment out of using foam board/spray foam insulation. It's too bad the whole house couldn't have been insulated with XPS.

Kelly, these are all good points. I was not aware that the classification of vapor retarder and barrier is subjective or dependant on application. Since XPS Was applied over such a small area (4'x6'), I won't worry about negative side effects. Worst case, if I notice any issues in the attic or with the drywall in the bathroom, the access is about 8' from the shower.

I ended up notching 2x4s with a hammer and chisel. Time consuming, but not as messy. Turns out the kerdi niche won't be here today, loaded on UPS truck but they don't make deliveries today in my area.

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Old 12-29-2018, 04:42 PM   #67
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Originally Posted by CX
As to your XPS being a retarder and not a barrier, that would depend upon the quality and thickness. Some of that extruded foam is pretty dense and you can get below 1 perm with less than an inch.
Just circling back on this - the perm rating for 1Ē of OC Formular 250 is 1.5 for an inch, or .75 for a 2Ē panel. When using that type of foam myself, Iíve always left about a half inch gap to allow some air in. Wonder what the best choice is going forward? For Ali he feels comfortable as is, but a good practice . . .?
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Old 12-29-2018, 05:38 PM   #68
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Good question Kevin, I'm also curious about this for future projects. As it stands, I have .25" between the 2" XPS and where the drywall will go.

Small update, framed the 12"x28" kerdi niche. Had to use shims because it looks like the builder picked up all the clearance 2x4s from Home Depot.

Shower is now 100% ready for drywall.

Question for those who have experience with fixed frameless shower panels. I'm debating on going with a 48-52" fixed panel from the wall where the door is located. Pros/Cons? For reference, the rain shower head is 30" from the wall. My wife thinks the water will splash outside of the curb area and get the floor wet.

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Old 12-29-2018, 06:46 PM   #69
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I am an amateur when it comes to building science but I have read a lot in the past about energy efficient houses and various insulation practices. I've learned a lot from the well-researched and well-argued writings by Martin Holladay and Allison Bailes. Green Building Advisor has a lot of great articles about spray foam, focusing on both, strengths and weaknesses.

Here's a good article describing what Ali has done:
https://www.greenbuildingadvisor.com...ble-insulation

In order to significantly increase the R value of your wall assembly and to overcome the thermal bridging of all the framing material, you would have to introduce a continuous layer of foam covering your wall either from the outside or the inside. For me, that meant sacrificing 1/2 inch on the inside of my exterior bathroom walls (since I have brick veneer on the outside). For me, it was totally worth it as one of my bathrooms is in a corner of my house and has two significantly long outside walls. Altogether, I prefer fiber-faced polyiso foam panels over foil-faced panels or XPS as they allow for slightly better vapor management.
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Old 12-29-2018, 07:40 PM   #70
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I'm debating on going with a 48-52" fixed panel from the wall where the door is located.
What size glass? From where to where? How wide is your shower?

I’m sure I’m misunderstanding but if you had a 60 inch wide shower for instance and you put in a 52 inch wide fixed panel glass, that would mean you’d only have 8 inches wide to get into your shower.

Did you mean 48“ x 52“.

Regarding splash: If you are using tile for your floor you can certainly run Ditra under your tile, and or run your Kerdi membrane over the curb and onto the floor for some distance
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Old 12-29-2018, 08:03 PM   #71
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Glass would be 48-52" x 72". It would extend from the wall across the curb that is 64". On the other side where the half wall is, there is a 17" curb there. Ideally, I'd like to walk into the shower diagonally where the bumpout is next to the half wall and not have to deal with doors.

As for the floor tile, it was installed by the builder's tile contractor. The guy couldn't build a shower worth a shit but his floor tile was ok by my standards, so we're not ripping it out right now. Unfortunately, here won't be a good way to waterproof the floor with ditra

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Old 12-30-2018, 06:54 AM   #72
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If the fixed shower head was on the wall housing the valves, you'd be fine. But with the centrally mounted rain head I'm betting with Mrs. Ali, Ali. Although, rain heads - in my very limited experience, don't operate with the same pressure as a "standard" shower head - which'll help, and also don't have the same cone/ shaped spray pattern, which'll also help.
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Old 12-30-2018, 09:48 PM   #73
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You make a good point Dan, might go with a full glass wraparound either framed or frameless. When the tile is all done, I'll do some trial runs.

I picked up the drywall today, galvanized screws, and a tube of Sika construction adhesive. The plan is to bed the screws roughly 1/8-1/16" into the drywall, and put a dab of Sika over the hole prior to mortar and kerdi. Overkill? Probably, but I don't want rusty screws holding up the drywall after wet mortar cures over it.

Used drywall shims to fix all the bowed, crooked, and out of plane 2x4s. The walls are all level and plumb now. I also used drywall shims to help slope the curb. Taking Mrs. Ali to dinner tomorrow for NYE and booze in the evening so my next update will be Tuesday when the board goes up.

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Old 12-30-2018, 10:14 PM   #74
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The plan is to bed the screws roughly 1/8-1/16" into the drywall, and put a dab of Sika over the hole prior to mortar and kerdi.
Ali, you really don't wanna do some of that. The moment you break the paper on your gypsum board by countersinking the fasteners you've dramatically reduced the pull-through resistance of the drywall panels. You really want the heads flush with the surface and no deeper.

Your galvanized screws will resist the moisture of the thinset mortar long enough for it to dry after curing and will hold the drywall in place just fine.

My opinion; worth price charged.
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Old 12-30-2018, 10:23 PM   #75
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Good to know, I will save the tube of Sika for the kerdi install and flush the galvanized screws. Appreciate it!

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