Wanted to get the community's opinion on mounting my master bath faucets on an exterior wall & combating the possible freeze.

Could it be as simple as Macy's post below advocating spray foam?

vs.

A bit more complex like my builder who suggest thickening the wall by using 2 x 2x4 studs (furring out)?

Posted by macy (My Page) on Fri, Nov 13, 09 at 16:59

You can base your decision about the location of pipes on anecdotal information and other people's opinions or you can design the wall to avoid freezing of the pipe. If you choose the latter, you can use the formula normally used to locate the dew point in a wall in order to determine where the temperature would be 32 degrees or lower.

Ignoring air infiltration for a moment, a water supply pipe 1 1/2" deep in a 2x4 stud wall and insulated with 3 1/2" of fiberglass insulation would probably freeze at about -10 degrees F. Ironically, removing 1 1/2" of the insulation on the warm side would lower the outside temperature needed to freeze the pipe to about -50 degrees but for fiberglass insulation air-infiltrations makes that prediction unreliable.

So the design solution is to air seal the stud cavity and place R-10 or greater insulation on the cold side of the pipe. This is best done with spray foam (Icynene, etc.) and if the studs are 2x6's, the R value would be as much as R-14 which would put the temperature of the pipe at about 55 degrees when the outside air temperature is -30 degrees F. At that outside temperature the house temperature would need to drop below 45 degrees for the pipe to freeze. This design is roughly equivalent to a double 2x4 stud wall with no insulation in the interior wall and 3 1/2" foam or dense-pack cellulose insulation in the outer wall.

Here is a link that might be useful: Placing