Should you insulate hot water pipe (copper) located in an attic?

I live in Louisiana, where it rarely gets cold. The plumbers insulated the hot water pipe from the tankless water heater. Now condensation is building up between the pipe and insulation so bad, it leaked onto the Sheetrock over the laundry room causing damage. The plumbers tried to blame it on the rain, but the roofer said the roof is fine. Since I took off the insulation, the condensation is gone (and it has rained everyday). The Plumbers said rain made the insulation around the pipe wet, but the condensation is ony inside the insulation around the pipe. There is no water damage anywhere else.

  • C'm Laving a Rard time uNderstanding Kour question. Please edit.
    – BMitch
    Commented Feb 23, 2012 at 19:23
  • 3
    Sounds like the plumbers may be Milli Vanilli fans.
    – Tester101
    Commented Feb 23, 2012 at 19:37
  • Bad Tester. Naughty Tester. Shame. Commented Feb 24, 2012 at 14:14

4 Answers 4


Insulation on pipes should prevent moisture in the air from condensing on the pipes, by preventing the air from coming into contact with the pipes. What you are experiencing could be caused by a few things.

  • Insulation was not installed properly, and is not preventing the moist air from contacting the pipe.
  • Condensation is forming on an un-insulated section of the pipe, and is flowing along the pipe into the insulation.
  • The roof is indeed leaking.
  • A leak has formed somewhere along the pipe (remember, there is water in them there pipes).

But why don't I see the problem when I remove the insulation?

Removing the insulation may be allowing the moisture to evaporate before it can build up and cause problems. the insulation could have been preventing evaporation, which allowed a noticeable amount of water to build up inside of it. Once the insulation reached its saturation point, the water had nowhere to go but onto the floor.

  • @Steven en.wiktionary.org/wiki/them_thar
    – Tester101
    Commented Feb 24, 2012 at 13:02
  • Sorry @Tester101, the Canadian dictionary only has 400 words in it
    – Steven
    Commented Feb 24, 2012 at 13:07
  • @Steven Does that include Eh, Tuque, and Hoser?
    – Tester101
    Commented Feb 24, 2012 at 13:19
  • That, plus the correct spellings of words like colour and neighbour :)
    – Steven
    Commented Feb 24, 2012 at 14:18

The point of insulating pipes is to a) reduce heat exchange and b) prevent condensation.

You likely want your hot water pipes insulated primarily because of a.

But b could also come into play.

It's extremely humid in LA. And if the water in the pipes sits long enough (overnight) to cool the water, then come the next day, you may very well get condensation on them. The insulation will block the moist air from coming into contact with the pipe itself preventing condensation.

But I'd also look for roof leaks as well.


The most likely reason (except the roof being leaky of course) is that the insulation doesn't fit the pipes. It takes it being only slightly loose - and air gets between the insulation and the pipe and at some temperature change water gets condensed. The insulation should be installed tightly and all seams if any should be sealed with something like duct tape so that air is never in contact with the pipe surface.


People used to use steel pipes, but these rusted away when insulated. Hence the move to copper pipes. Any pipe that holds water that is below the "dew point" of the surrounding air will attract water vapor/condensation. I have bare copper pipes in my bathroom, the hot pipes stay dry, the cold pipes run with condensation while and after taking a shower. It is just a fact of life, carefully installed tight fitting water vapor proof insulation will stop condensation by presenting a warm surface to the water vapor laden air. Using a exhaust fan coupled to a humidistat will move the problem outside, better, an exhaust fan with a built in heat exchanger, this will help to prevent drafts as the exhaust fan struggles to find "make up air" leading to a warmer, cheaper to heat home.

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