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I have a rigid metal exhaust pipe coming out of the bathroom fan over my downstairs bathroom. It goes up at approximately a 30 degree angle for about twenty feet and stops just before it gets to the side of the garage, where it points, open, at a screen that seems to be mostly sealed (I don't know if this is how my attic over my house is supposed to be; I trusted that my roofer knew what he was doing). There are joints about one/third and two/thirds of the way up the pipe. The top third of the pipe is dry. At the highest of the two joints, there are a few drops of water, that I'm sure are being formed by condensation, then running back down the outside of the pipe, to soak my fiberglass insulation and then drip down through the bathroom fan while it is on.

My questions are these:

  1. Is this an immediate repair job, or can it wait until I have a week off in February? Could it wait until summer (when it will be warmer for me or the condensation won't(?) be occurring)?

  2. What would be involved in the repair? I'm thinking I'd need to replace any wet insulation, check the integrity of the drywall that forms the ceiling for the bathroom, and seal the pipe (somehow). Are these accurate and what haven't I thought of?

3 -- What is the proper way to vent the end of that pipe out of my attic with that side vent (I wish I knew proper terminology, sorry; I'll try to get some pictures up here to help)?

  • General tip: Don't trust an x to do know what they are doing when it comes to y. For example, don't trust a plumber to know what they are doing when it comes to adjusting the framing to make room for plumbing. And don't trust a roofer to know how to run a bath vent. Or perhaps more accurately, it's not that they don't know the better way, they just weren't hired to care about that particular part of the job. – DA01 Jul 14 '15 at 1:02
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The vent should be going directly outside, not venting inside the attic near a screen. Also, the pipe should be covered in insulation to prevent the warm humid air from cooling down so much that the water vapour condenses and runs down the pipe into your bathroom. This might be damaging your ceiling drywall, which is a pain to repair.

  1. Extend the pipe through the exterior wall. Use an exterior vent with a damper, so wind does not blow cold air into your house in winter. There a a couple of different types of dampers, and the vents come in many colours and sizes to suit the exhaust pipe (can be various shapes and sizes), a 4" round vent is most common in North America for bathroom venting. This can wait until February (it's already been years, I'm guessing - so another month shouldn't make any significant difference).

  2. Insulate the pipe. You can get pipe insulation that slides over the pipe. If possible, you should do this now, to stop any further water damage.

  3. If your insulation is soaking wet, replace it.

  4. Repair your drywall if there has been water damage. Be sure to use a stain-blocking primer before repainting the ceiling.

  • Thanks so much! I can do the insulation and the insulating of the pipe this weekend I hope. Forgive a potentially stupid question: I know touching insulation with one's bare hands is not recommended. I can test if the surface is wet with a paper towel or some such, but do you have any recommendation for seeing if it is sodden? I suppose just pull it up with work gloves and a good flashlight, yeah? – Mark Palise Jan 12 '15 at 23:04
  • Touching fiberglass insulation isn't recommended because small fibers can get into your skin and is itchy. If you are removing insulation, I would suggest also using a mask to keep any dust and fibers out of your lungs. You can use work gloves but they can be clumsy. I use nitrile gloves when working with insulation, although I did use the yellow rubber kitchen gloves one time. – Mark Jan 14 '15 at 5:17

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