Insulation, Radiant and Vapor Barriers - Interior Bathrooms - Insulation / Sound Retardant

My master bathroom and guest bathroom share the same wall. I recently remodeled the master - installed greenboard in general bathroom area and roofing paper as vapor barrier and cemet board for tile substrate.

There wasn't any insulation between the two bathrooms when I remodeled - which I understand to not be uncommon. With that said, I'm going to remodel the guest bathroom and would like to put some insulation in the wall to lessen the sound you are able to hear from the other bathroom.

I'm looking for suggestions on brand and type/model of insulation. Any suggestions?

Also, obviously there are many pipes between the wall i.e. sewer exhaust pipe, sink hot/cold pipes and shower hot/cold pipes. Anything I need to take into consideration with the pipes or electrical outlets?

And last on the list, because the wall is between two bathrooms I don't imagine I need to install a vapor barrier, other than what I installed for the shower, correct?

Thanks,

Darby

I'm interested in the answer to this question as well. I hate hearing the sound of water (and other bathroom noises for that matter!) thru the walls...

Any moderator/expert available to reply?

Installing insulation between two conditioned spaces have little or no thermal value. The insulation can provide some sound deadening effect.

Vapor barriers deal primarily with heat transported moisture from a high pressure area to a low pressure area. Or if you prefer, a conditioned space to an unconditioned space. Clearly vapor barriers do not apply in this application.

Moisture Barriers do apply and the most common found in bathrooms are tub surrounds. You may wish to continue this application on any wall, ceiling and floor penetrations. For example, a very common place to mold and mildew in a bathroom is around the bathroom exhaust. In most cases the opening for the exhaust is larger than the fan itself. Because of this opening if you were to examine the sheet rock above the ceiling, you would find mold and mildew. An easy solution is to duct tape the opening between the sheet rock and the fan in a way that the cover hides the tape when installed. This applies to light fixture, electrical outlets and switches and especially plumbing pipes under a sink. Unlike Vapor barriers, Moisture Barriers deal with the fluid aspect of moisture. And Yes, the moisture in this situation in air is considered a fluid.

As far as the pipes in the walls are concerned, by all means insulate them. Not only is it easy to do, it is also inexpensive. However, the pipes you are most concerned with are your cold water pipes. This is because heat condenses on cooler surfaces. Example, a soda can sweating when taken out of the refrigerator during the summer. Because of the high humidity associated with bathrooms and the temperature of the cold water pipes, the cold water pipes have the highest probabilty of condensation occurring on them than any other material inside the wall.

Inside the wall itself you will find penetrations from one level to another. Again the opening for pipes and wires are usually larger than the pipes and wires. I seal these opening to prevent fire from having an easy access to the next level of the house. The side effect of sealing those penetrations inside the wall is that it dramatically reduces the convective loops found inside walls. Even though insulation does the same thing, the insulation does not have the same effectiveness to stopping fires as sealing the penetrations.

Fire stops like these merely in this application provides some more time for the occupants to escape and/or for someone to put out the fire, thereby limiting the amount of damage a fire may cause. Real fire stops use fire proof materials, which means you will never see plastic piping used for drain pipes that penetrate one level to another in a house and the sealant themselves are fire rated.