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Old 01-25-2019, 08:42 AM   #1
guoxiaotian
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Pipes freezing behind Kerdi board?

Hi all,
The small alcove shower(34x38) in the bathroom I am remodeling, has its plumbing fixture in exterior wall (6-inch). It had to be done this way because the opposite wall has 2 DWV pipes, including the main stack running through it.
For the last 30 years it worked fine. Behind the one piece 1/4" faux granite waterproof sheeting, are drywall sheets. the copper pipes in the exterior wall were installed closed to the drywall and the heat from the interior would keep it from freezing.
My plan is to use 1/2" kerdi board for waterproofing, but yesterday I just realized this could be problematic, as the R value just bumped from drywall's R0.5 to foam board's R2.2. I am worried the pipes no longer get necessary heat from inside to keep them from freezing.
Am I overthinking this? is the 0.5 -> 2.2 significant enough to make a difference? If so what are my options? One option I can think of is using Durock cement board (R3.9) but it would complicate my installation.
I am in Seattle, winter isn't extremely cold, but we do get several cold days (in 20s) in winter.

Thank you,

-XT.
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Old 01-25-2019, 08:55 AM   #2
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If your wall is properly insulated behind the water pipes I would not expect that change in interior wall covering to cause a freezing condition where none existed before. See my warranty information below.

My opinion; worth price charged.
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Old 01-25-2019, 07:12 PM   #3
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It helps if you put your general location in your signature line or profile. While many places may see freezing weather, the duration and severity can vary radically, and that may change some thoughts on the results.

The pipes may be run close to the interior wall, but the valve body tends to be much further back into the wall. Many more modern homes used 2x6" walls, allowing more insulation, but there won't be much room behind a 2x4 wall to the actual exterior, so very little insulation could be there. FWIW, pex won't split if it freezes, but that doesn't apply to any fittings it might go through.
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Old 01-25-2019, 08:08 PM   #4
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Says he's got a 6-inch wall, Jim.

And while PEX tubing is more resistant to splitting than copper, I wouldn't go so far as to say it won't split after a few freeze/thaw cycles.
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Old 01-25-2019, 09:03 PM   #5
guoxiaotian
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Yes it's got 6-inch exterior wall. I am also less worried about the valves themselves, as the interior wall has 4-5 inches opening only covered with escutcheon, which probably has R-0. plus I am not making it worse than before.
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Old 01-26-2019, 05:46 AM   #6
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Not sure what the 1/4" faux granite waterproof sheeting is, XT. But if you intend to have drywall, the WP sheeting, then Kerdi board....well, all you need is the Kerdi board. I don't think you want Kerdi board on top of that WP sheeting - sounds like a moisture sandwich.
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Old 01-26-2019, 12:38 PM   #7
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You don't say what insulation you have. If fiberglass, then there's a chance that through air leakage and convective currents (plus possibly poor installation) you're losing insulation value anyway.
You could air-seal the perimeter of the cavity with a thin bead of foam in a can (Great Stuff) and then put the batts back in, tucking enough insulation between hoses and outside sheathing. Or you could be proactive and treat the whole cavity with foam (something like "cut and cobble"). Another way would be to primarily encase the pipes and valve in foam, especially filling all the space where they're facing the exterior sheathing. I think that should prevent any pipe freeze unless your house is unoccupied/unheated for longer stretches during the cold months. But in that case, all bets are off anyway.
Altogether, this strikes me as a concern that can be easily solved with modern insulation methods.
And no, I don't think the Kerdi Board's insulation value is great enough to cause a concern.
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Old 01-28-2019, 11:48 AM   #8
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When I finished in my basement, I had to contend with some plumbing along outside walls, namely copper pipes feeding outdoor hose spigots.

The thing I did was to use 1/2" foam board insulation behind the plumbing (where possible) and beside the plumbing (stacking it up to the thickness of the wall), leaving an un-insulated channel from the plumbing to the interior wall... the idea being to provide a way for some of the warmth of the room to reach the copper pipes.

Now I'll admit that I live in Alabama, where "bitter cold" is defined as anything in the twenties. But we still usually get at least one night of the year where the night time lows drop into the upper teens.

The hose spigots mentioned above have been plumbed with "frost free hose spigots", and I never drain the pipes for the winter. It's been about 8 years since I finished the basement and haven't had a busted pipe yet.

The layering for my most exposed pipe was something like this (outside to in):
Brick Veneer
Tyvek House Wrap
1/2"OSB sheeting,
1/2" foam board insulation
1/2" copper pipe
air
1/2" Hardie Backer
AquaDefense
Thinset
Thick Tile (suitable for floors and walls).
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Old 02-17-2019, 05:19 PM   #9
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Distance between shower enclosure and drywall

Is there a minimal distance between shower enclosure and the joint between drywall and backboard panel? (see attached picture)

I am sketching up tile layout and need to determine where drywall and backer board should meet.

Maybe I am paranoid, but my concern is that if that spacing is too small, water from inside the shower will get behind the tile through grout, since I am using foam based board(like Kerdi board), which will not absorb any water, water will move between tile and board and eventually reach the drywall panel and ruin it.

Thanks,

-XT
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