My son just bought a new house in Calvary, Alberta. The last few nights have been approximately -30 °C (-22 °F).

When he was cleaning his second floor guest bathroom, he noticed a stain on the ceiling of the main floor directly under that bathroom. He called the builder right away and their plumber looked and said the stain is caused by condensation on a pipe in the unfinished attic space thawing and dripping down the pipes. My son lives alone and works full time so he is not there running the water and steaming up the house a lot.

  1. Would there have been any reason to run a pipe through an unheated attic in a new build in cold weather?
  2. Should they be looking for bigger problems like incorrect insulation or leak in envelope?
  • 2
    What kind of pipe? If it's a vent pipe there's a great reason to run one thru the attic - they have to. Commented Dec 30, 2014 at 19:27
  • Whatever the reason, it's already causing issues try to focus on only the solution. First prove the diagnosis is correct. Then if so you can attempt to add insulation around the pipe to stop the condensation. Commented Dec 30, 2014 at 21:45
  • Legal questions are off topic here. I've removed that part so we can address the parts that are on topic. Can you describe what types of pipes are seeing condensation? Are they exhaust ducts, drain vent stacks, cold water lines, HVAC condensation drain lines, or something else?
    – BMitch
    Commented Dec 31, 2014 at 1:36

3 Answers 3


What kind of pipes are in the attic space? There should not be any water pipes otherwise you have a risk of burst pipes. It sounds like there is a problem with the vapour barrier having gaping holes and missing or insufficient insulation.

A common problem with attic fans is that the ductwork is cold and when the fan is switched on for showering, then the humidity condenses in the ductwork and can run back inside the fan housing.

This doesn't sound like excess moisture -- to me that would mean a lot of moisture on the windows, for example.


-30 C is really cold and typically very dry - I don't see how this could be condensation

next- who runs a water pipe in an attic? why would you run a water pipe in an attic?

Is we saying they ran a hot air conduit through the attic? even if he did- cold air is dry so there is no condensation. Interior heated air might have condensation in the hot air conduit- but that is in the conduit.

earlier poster is right on the vent pipes- if you were in warmer weather I would expect a leak around the vent boot - very common - especially in weather as extreme as yours. But at -30 - don't think so.

if you have a leak on the main floor- under a bathroom- Occam's razor says the leak is from the bathroom. You now know the builder's character by his response. Start communicating in writing and keep a copy and a log of every time you talk to him. Tell your builder you are going to consult a lawyer - then do it. My experience with these types of builders is they need their arm twisted.


It sounds like further investigation is required to be certain about the cause of the problem. For example, is the stain wet or dry - was it caused by a one-time water spill or is it a continuing problem. An unbiased third party like a home inspection company could provide assistance by using an infrared camera to "see" the temperature difference between wet and dry ceiling. Or a remote video probe could be inserted through a small hole in the ceiling to see what is above the stain.

I also have a new home in Calgary and have not had problems with condensation on vent pipes.

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