I am replacing some crumbling hardboard siding panels on the back of my house (north facing wall) in Austin Texas. I discovered under the kitchen sink window that the water pipes come up out of the concrete VERY close to the outer face of the foundation. The copper pipes are in one of those plastic sleeves to protect them from the concrete and they have black foam insulation on them. There is a part right where they exit the concrete that is uninsulated and the wall cavity had some fiberglass stuffed into it. I am trying to decide what I should do with this situation, if anything. I considered filling the void with expanding foam, but as people in other threads have pointed out, the inner face of the pipes should be left clear to allow heat absorption from the interior.

Our standard practice in freezing weather is to drip faucets and open cabinet doors under sinks. We haven't had any issues, even when it got to 5º during the winter apocalypse in 2021. While I have the wall open, I want to improve this situation - if I need to.

Any thoughts?

pipes pipes_side

  • 1
    Don't know if this was the intent in this case but what that sleeve insulation actually does for you is keep the pipes from sweating. Moisture from hot humid air can condense on them when they're cold on the outside from the cold water inside. Jun 12, 2023 at 14:06

1 Answer 1


Texas plumbing. It freezes, but y'all pretend it never does, making it an apocalypse when it does.

I would suggest removing the fiberglass (in this stud space, anyway) entirely and installing either XPS or Polyisocyanurate rigid foam sheets between the pipes and the outer wall surface. Perhaps even a U shape so there's also sheet foam between the pipes and the studs, since studs are not very good insulators themselves.

Do a really nice job and save some on your AC bill too by sheathing with an inch of foam before you get to the siding, over the studs. That may be difficult if you are only working on a limited part of the wall rather than the whole wall, though.

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    Yeah, the only good solution is to properly insulate the building envelope, which is outside the plumbing. Put foam on the entire wall.
    – isherwood
    Jun 12, 2023 at 13:14
  • Agree, except this wall is the ground floor on a two story house. If I added a layer of rigid insulation, the siding panels would stand proud of the upper panels with no way to direct water to the right places. I have a full energy retrofit planned and hope to start that soon, but for now I can't justify expanding this project to add that foam. This is however exactly what I plan to do in the future - adding out-sulation over the the entire building envelope and adding a modern WRB instead of the tarpaper used in 1993. None of it was installed properly back then.
    – Metl Mann
    Jun 12, 2023 at 20:36

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