I am looking into ways of insulating my master bath as I put it together, I’m down to the studs at the moment.  I live in Sunny SoCal, where the temp averages 75 degrees and very low humidity nearly every day of the year.

My bathroom shares on wall with a guest bedroom and one with an exterior wall.  The tub/shower will be against the exterior wall.  The exterior wall is 2×4 with tar paper under 3/4″ stucco.  The tar paper isn’t in the greatest shape, but the little rain we do get doesn’t come from the direction of that wall anyway, so I am not worried about water intrusion from this wall.

I was thinking about using a 2 part polyurethane foam sprayed into the stud cavities, both for insulation and improved structural rigidity on the exterior wall.  I would also use it to insulate the Hydro Systems Solo spa tub, if it wasn’t already done.  In addition I would put a thinner layer on the inside face of the drywall that faces the wall to the guest bedroom to help deaden sound, then supplement this with cellulose and maybe another layer of foam under the Denseshield drywall – all this to stop plumbing noise and other “bedroom” noise from reaching the guest bedroom.

I was thinking the FROTH-PAK 120 kit might be the way to go.  Alternatively, I also have a can based gun foam setup, which of course is more bead oriented rather than wide surface.

What do you think about using foam in this way, and is the $220 FROTH-PAK 120 the way to go or should I just use a bunch of $12 cans of gun foam for this small project instead?

Attached is a picture of the wall that would be insulated.  There are some areas of water rot I’ll be replacing before any insulation.