We're converting an old bathroom addition in our house to be a utility/laundry room. The bathroom wasn't properly vented or sealed, so we are completely gutting the room to deal with mold and mouse damage.

We've already removed the old shower plumbing, which was behind a false wall, as well as the false and underlying interior walls as well. We've run new pvc supply and waste lines up through the crawl space and into the floor, where the washing machine will be located. The pipes are about 8 inches away from the sheathing of the exterior wall:

new pvc pipes and waste line

How can I protect this from freezing? We're in Bloomington, Indiana, which has gotten as cold as -12F (-25C) in the dead of winter. The wall itself is fairly exposed, as it is a corner room sitting on top of a half-exposed crawl space.

My initial thought was that, since this is effectively a double-thick wall, we could just use two layers of fiberglass and then throw our drywall on top of that. Alternatively, we could use some combination of foam, fiberglass, and pipe insulation. Would that be good enough, or should I create a more rigid barrier? If mice get into the wall again, they could damage any softer insulation that we use. Do I need to go through the trouble of building an entire false wall, or could I just build a little protective box around the pipes? Should I install an active heating element as a backup, like a pipe-heating cable system?

  • 1
    Is this area going to be heated? I love heat tape but haven't seen any that is listed for use in walls.
    – Ed Beal
    Commented Sep 4, 2018 at 18:49
  • @EdBeal it will be a heated room, via a floor duct about 5 feet away.
    – alexw
    Commented Sep 4, 2018 at 19:10
  • If this will remain a bathroom, you will want to install Hardy Board. Green colored board like drywall but blocks moisture and mold.
    – stormy
    Commented Sep 11, 2018 at 22:17
  • Nope, converting it to either a laundry/utility room, or mud room (or both).
    – alexw
    Commented Sep 11, 2018 at 22:20
  • A transition room where lots of moisture will be produced. Hardy backer board is a green drywall thing 3' X 5' X 1/4" that is rot resistant. Hardy plank is a concrete lumber sized board that replaces traditional wood siding such as cedar. Cold exterior and warm interior means condensation and that is why the ventilation is so critical. Treat this just like a bathroom with a shower. I've got to go look this up again...I'll be back. Arguing with my hubby, grins. Condensation forms on the outside of the plastic covering the insulation. or rather forming next to the insulation. Ugh.
    – stormy
    Commented Oct 3, 2018 at 21:07

2 Answers 2


I've had this problem and it gets passed up in inspection a lot of the time. I would build a separate box around these pipes, insulate and even use heat tape. Plumbing on an outside wall like this will freeze! Even a concrete outside wall 8" thick. Put the heat tape on a separate line so that you decide to turn it on when necessary. Insulation could be fiber glass, blown in insulation or even shredded newspaper. Newspaper is great insulation. I'd use something that is fire retardant for insulation if you use electrical tape.

How long ago was this installed? In Washington State, there is 12 years for discovery and getting something fixed by the general contractor no cost to you. There are ways for contractors to get out of this clause in Washington States laws but few understand the laws, even lawyers are clueless.

Check out the laws in your state. If you did not sign a contract that says, "Indiana's State law for warranty is superseded by this contract declaring a one year warranty to include labor and material..." then that contractor is obliged and has to abide by the warranty law in your state. Worth checking out. You have to hire a licensed plumber to fix this, you should not do it yourself because it might VOID the warranty protecting you.

I would hire a free lancing home inspector. Very reasonable costs! They work for you! Not the city or county.

  • Thanks! Our friends installed the lines when they came to visit a couple weekends ago, so no concerns about a warranty there. I probably won't use newspaper since it is such an attractive nesting material for mice. I'll build the separate box, insulate it with fiberglass, and install the heat tape!
    – alexw
    Commented Sep 11, 2018 at 21:45
  • 1
    All insulation is wonderful for mice. And some of it if it catches on fire produces a ton of toxic gas that makes it difficult just to get out of the house on fire. An inspector knows all of this. You could and should sleep easier if you get an expert home inspector out to see this before you make any other decisions. Another warning; if you hire friends, contractors without licenses this could also negate your home owner insurance policy. I strongly advise hiring an inspector at this point! After a fire they find some wiring or improper materials used, insurance is voided.
    – stormy
    Commented Sep 11, 2018 at 22:08
  • The best insurance against rodents are cats! I prefer my cats to stay indoors but recently I had a feral have kittens. Just trapped them all except 4 of the extended family that aren't regulars. We now have outdoor cats (8 just came back from the spay and neuter people) and we will never have to worry about mice, rats, chipmunks, few baby bunnies are able to make it and birds are few. Cats are amazing to add to any family and home.
    – stormy
    Commented Sep 11, 2018 at 22:14

What is the code requirements for insulation of an exterior wall? If the pipes run on the face of an exterior wall then it is in a heated area and not the concern. Might not be appealing though hence the dummy wall.

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