Hello - a bit of a preplexing issure I have here...

In an upstairs apartment, we recently found mold in a closet. The closet is in the back left corner of the apartment (the joining of 2 exterior walls). At first, we assumed that this mold was due to a leak in the roof, but I am beginning to believe that
Is not the case.

The entire apartment seemed very wet, and there was a large amount of condensation on the windows. We purchased a dehumidifier and found that the apartment had a whopping 85% humidity level. I am beginning to think that the moisture in the closet was simply due to condensation of the humid air on a cold (exterior) wall. The apartment is made of brick & concrete block without insulation, so the exterior walls are fairly cold.

I placed this question in the heating section, because I am wondering if a problem in the heating system (hot water baseboard radiators) could cause such a high humidity level in the apartment. I find it hard to believe that a small leak in the roof could cause such a high humidity level, however I have been unable to find any information about baseboard heating problems causing high humidity... any help would be greatly appreciated.


Thank you!

Older homes were not insulated as they are today and due to the lack of insulation and a moisture barrier the moisture will come through the walls and cause mold especially in a closet where there is no air movement when the door is closed.
With a humidity level of 85% it is very understandable you may have a mold problem, the fix may not be as simple, insulate with a vapor barrier, replace windows with thermopane windows, for now I might suggest leaving the door to the closet open for air circulation try spraying the molded area with bleach to kill the mold. As a note , when you raise the room temperature you decrease the relative humidity. Good luck, Mike

Thanks for your input... let me add some more info to this problem...

First of all, the previous owner had indicated a mold problem in the same closet -- so when he had the roof completely redone and the brick re-pointed, the closet was also rebuilt with a vapor barrier included. The windows in the home are all new vinyl double pane windows.

This apartment is also one of 4 in the building -- it is a rectangluar shaped 2-story building with 4 identical apartments. None of the other apartments have, or have had, mold problems at all. My feeling is that the humidity is causing the moisture on the walls -- which in turn is causing the mold -- but I am trying to pinpoint the source of the humidity. There is only 1 bathroom so that is not causing much more moisture than normal, and there is not an excessive amount of cooking going on. The best source of water I can come up with is the baseboard water heating -- but I haven't been able to find anyone who has noted problems with hydronic heating leading to high humidity.


I understand that higher temperatures decrease the relative humidity -- however that does not decrease the actual amount of moisture in the air. At 85%, it is inevitable that moisture will collect on all cold surfaces (exterior facing walls, windows, etc... )...

Here a few addendum's to the previous answer. ONe question I would have are the age of your windows. If their seals are broken, the dewpoint will actually occur inside the layers of glass and on the inside of the window.
Next. To ventilate the closet, there are decorative vents that can be purchased to allow some airflow out into and out of the closet.
Next. Be sure that your bathroom vent and range vent are unobstructed to the outside. ONe house we had gone to to weatherize had ENORMOUS amounts of humidity in it. Turns out the vent from the dryer had come unhooked and was ouring humid air straight back to the house. Consider installing more powerful vents in any event to draw out the humid air more quickly rather than have it circulate through the house.
Make SURE the attic insulation is sufficient with proper ventilation. You'd know you have a problem if there is loads of frost/or moisture clinging to the rafters.
Let me know if you'd like on what you find.

You didn`t say,, but what kind of a/c system if any do you have? Is the mold and humidity problem the same?worse?or better in the summer season,, you may need more than one de-humidifier

So this was a 2-year old question, however I fairly confidently believe that I have found the answer, so I figured I'd post it just in case anyone else has a similar problem.

As noted, the apartment was subject to excess moisture. My hunch was that it was coming from the baseboard water heaters. A few months ago, we determined that the auto-fill valve for the boiler was not working and would not regulate the pressure inside the boiler tank.

We immediately turned it off, then replaced it, and since that time the humidity has not been anywhere near where it was in the past. I can all but assume that the over-pressurized water was somehow being forced out of a radiator and into the apartment.

Hope someone can use this information!

Jason