Wet Bathroom Walls and Ceilings

Discussion in 'Shower & Bathtub Forum & Blog' started by JJLJr, Oct 29, 2007.

  1. JJLJr

    JJLJr New Member

    Rhode Island
    I recently purchased a house. The bathroom did not have fan and so I knew eventually I would have to install one. Over the last few days, my wife and I have noticed some small mold spots on the ceiling. The spots look like someone took a pencil and started poking onto the ceiling.

    Over the weekend, I installed a new combo light/fan. The bathroom is about 60 sq ft with a 7 1/2 ft ceiling. I installed a Broan 683L which moves 80 CFM and is 2.5 sones. The fan is installed in the ceiling next to the tub. I vented the fan through the soffet with about 8 ft of flex duct. The duct work is straight with no bends except there is a 90 degree elbow at the soffet and a soffet vent on the end.

    I tested the fan to make sure it was moving air. I placed my hand at the soffet vent and felt a lot of air. I figured the wet walls and ceilings would be gone. However, when my wife took a shower, the walls and ceiling in the shower area were still very wet. We did let the fan run for 10-15 minutes after the shower and that seemed to dry everything.

    I have a coouple of questions. With a the size of the bathroom, is unrealisitic to expect the ceilings and walls to be dry right after the shower? Is there anything else we can do to help reduce the moisture? I usually leave the door open slightly to allow air to get into the bathroom. Is that a good idea? Also, I know the house has inadequate ventilation in the attic and an inadequate amount of insulation. I plan on having a ridge vent and soffet vents added and will then add more insulation. Will that help the moisture problem? We don't have mold in any other room.

    Thanks for your help.
  2. jimbo

    jimbo Plumber

    San Diego
    80 CFM is appropriate for your size of bathroom. That amounts to 10 air changes per hour, and 6 to 8 changes per hour are normal design goals. You should not expect that amount of air flow to completely dry the walls and ceilings. Just the air flow will go a long way in reducing mold growth, but not necessarily eliminate it completely. I prefer a larger fan, like 100 or 110 CFM, but that is not really necessary. It is a good idea to run it like you do for a few minutes after the shower.

    If you have a tendency to take "steam bath" showers, that is a tremendouse humidity load you add to the room each time. A bigger fan could then be appropriate.
    Last edited: Oct 30, 2007
  3. Chris75

    Chris75 Electrician

    Litchfield, CT
    I would install a timer switch and let the fan run for a good half hour after the shower... and did you actually install a soffit cap or just stick the duct work at the soffit itself?
  4. cwhyu2

    cwhyu2 Consultant

    Cincinnati OH
    exsust vent

    Inyourbest interest to vent out the roof,If you go the soffit way make
    sure you have vented to the outside completly.Timer is good.Yes you need a cap of some sort.
    Last edited: Oct 29, 2007
  5. JJLJr

    JJLJr New Member

    Rhode Island
    Thanks for the replies. I did place a vent cap on the soffit. It has a damper on it and is faced away from the house so that most of the moisture will be sent out past the soffet and up in to the air.
  6. leejosepho

    leejosepho DIY scratch-pad engineer

    Along with the timer, I also have a dehumidistat to run the exhaust fan even longer if the humidity is still high after the timer runs out or if the timer never gets turned on in the first place.
  7. tonykarns

    tonykarns In the Trades

    Does not matter

    You could put a barn fan in your bathroom and it would make no difference in some cases. The best thing to do, from my experience, is to paint with mold resistant primers and paints when it comes to bathrooms. The ones I use are guaranteed for 5 years against mold or mildew. Leaving the door to the bathroom open certainly helps. Most people have their water set so hot its like being in a steam room instead of a shower which does'nt help. Steam equates to humidity which in turn leaves moisture droplets. In large bathrooms some people are turning to small de-humidfiers to keep bathroom moisture in check. I would start out by using mold/mildew resistant primers and paints. Oh by the way I ALWAYS use exterior paint in bathrooms with a satin finish.

    Hope this helps

    Last edited: Oct 31, 2007
  8. JJLJr

    JJLJr New Member

    Rhode Island
    Something else I noticed. I'm not sure how to describe it. While taking a shower, the wall gets a little darker around the the shower head. It seems to creep up the wall and then spreads when it reached the ceiling. At first, I thought the shower head pipe was leaking but it isn't. The longer or hotter the shower, the larger the patten on the wall. Has anyone seen this? I'm sure it's all a part of the excess humidity from a hot shower.

    I was thinking of installing a low flow shower head and turning down the water temp on the hot water tank. Also, the soffit vent cap opening is smaller than the 4 inch duct work. Should I install a larger vent cap?

    Sorry for all the questions. I would like to get this resolved and move on to the next issue. Thanks to everyone that has responded.
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