ᐅ Damp spot in drywall ceiling of bathroom caused by pipe ventilation
Created on: 26 Feb 2025 12:31
G
Gerd&Jolanthe
Hello everyone,
I have a technical question and hope to get some answers from you. I have a newly built house, completed in 2020.
Topic:
It concerns the upper floor (bathroom).
At the time, I planned to install an exhaust fan in the bathroom to help remove humidity. I already installed the ducting back then, and a roof vent was fitted by the roofer for this purpose.
The bathroom ceiling was closed with drywall except for a small opening where the fan was supposed to be installed.
Later, I decided against installing the fan since there are two windows for ventilation in the bathroom, and I didn’t like the fan hanging in the ceiling.
The small opening around the exhaust duct, which was left open, was then closed afterwards with drywall.
In the winter of 2023/2024, I noticed that the small area of the ceiling had a different color tone and became slightly damp. At first, I thought it was caused by not properly finishing the small drywall piece I added later.
However, the problem worsened over the last few months. A stain appeared, and eventually, water even dripped from that spot on the ceiling.
My assumptions:
1. Moisture is entering through the exhaust duct.
2. Moisture from the bathroom is getting into the small closed drywall section and settling there.
Since the moisture caused dripping from the ceiling, this mostly happens when taking hot baths or when the girls take hot showers, mostly in winter.
Last week, I opened the area and found that the moisture is unfortunately coming from the ventilation duct itself, not from poor sealing of the small drywall section.
Now I suspect it is condensation forming when hot water is used, but this is only a guess.
I would like to simply fill the duct from the inside since it is not in use, either with expanding foam or mineral wool, or both, and seal the bottom with extruded polystyrene foam (XPS). Then I would close the open ceiling with drywall.
My question to you: Can this be done this way, and would the problem (moisture) very likely be resolved?
Or does the roof need to be opened up and sealed from above in that area?
Thank you very much in advance.
I have a technical question and hope to get some answers from you. I have a newly built house, completed in 2020.
Topic:
It concerns the upper floor (bathroom).
At the time, I planned to install an exhaust fan in the bathroom to help remove humidity. I already installed the ducting back then, and a roof vent was fitted by the roofer for this purpose.
The bathroom ceiling was closed with drywall except for a small opening where the fan was supposed to be installed.
Later, I decided against installing the fan since there are two windows for ventilation in the bathroom, and I didn’t like the fan hanging in the ceiling.
The small opening around the exhaust duct, which was left open, was then closed afterwards with drywall.
In the winter of 2023/2024, I noticed that the small area of the ceiling had a different color tone and became slightly damp. At first, I thought it was caused by not properly finishing the small drywall piece I added later.
However, the problem worsened over the last few months. A stain appeared, and eventually, water even dripped from that spot on the ceiling.
My assumptions:
1. Moisture is entering through the exhaust duct.
2. Moisture from the bathroom is getting into the small closed drywall section and settling there.
Since the moisture caused dripping from the ceiling, this mostly happens when taking hot baths or when the girls take hot showers, mostly in winter.
Last week, I opened the area and found that the moisture is unfortunately coming from the ventilation duct itself, not from poor sealing of the small drywall section.
Now I suspect it is condensation forming when hot water is used, but this is only a guess.
I would like to simply fill the duct from the inside since it is not in use, either with expanding foam or mineral wool, or both, and seal the bottom with extruded polystyrene foam (XPS). Then I would close the open ceiling with drywall.
My question to you: Can this be done this way, and would the problem (moisture) very likely be resolved?
Or does the roof need to be opened up and sealed from above in that area?
Thank you very much in advance.
G
Gerd&Jolanthe7 Mar 2025 09:19Tolentino schrieb:
Insulation alone won’t be enough; you need a vapor barrier from the interior to the attic space. Apparently, the OSB board on the rest of the roof serves this purpose. However, it is not airtight around the pipe penetration. Ideally, this should be completely sealed, preferably with a collar (although I don’t think there is an officially approved solution for OSB boards in this case). Can you access this from above? So, can you look at the pipe (and the OSB board) from the attic? Hi Tolentino,
In this area, I specifically used a small piece of OSB board, which was actually intended to mount the exhaust fan. The rest of the ceiling consists of drywall panels, and I wouldn’t be able to mount the fan there.
I can’t reach it from above either. The ventilation pipe runs directly and shortly up to the roof, where there is a roof vent.
Regarding the vapor barrier on the interior side:
- I could cut the pipe flush with my blue vapor barrier foil at the ceiling, as the pipe still extends slightly into the room.
- Then I could insulate the pipe from the inside (matching the pipe diameter) with XPS foam boards (I still have some of those).
- After that, I could seal the pipe opening with blue foil and green vapor barrier adhesive tape (Rissan).
- Additionally, I could roughly cut an OSB board and insert it into the open ceiling space. I would seal the edges of the OSB piece with acrylic or silicone.
- I would then insert a drywall piece into the open ceiling and apply four layers of joint compound. I would use joint tape on the seams after the first layer.
- I would sand everything and then paint the entire ceiling white.
Question: Is an OSB board or OSB ceiling also considered a vapor barrier, or is the vapor barrier only achieved with the blue foil?
Thank you both very much again.
A
Allthewayup7 Mar 2025 18:05OSB or similar materials are not vapor-tight. Only the membrane provides that.
G
Gerd&Jolanthe10 Mar 2025 07:11Okay, would the individual steps I described in the last message be sufficient?
Similar topics