Replacing drywall with kerdi board and freezing risk

[Xiaotian Guo]

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.

 

[Reach4]

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.

Put foam insulation between the pipes and the outside -- not between the pipes and inside.

 

[Sponsor]

 

[Xiaotian Guo]

@Reach4 the pipes will have Fiberglass batt behind it, the foam/Kerdi boards are for shower waterproofing, but have the side effect of keep pipes from getting heat from interior compared to drywall sheets.