GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Toilet overflow caused water to enter the ceiling cavity: How to remediate?

cconti | Posted in General Questions on

Hi all,

An issue every homeowner faces now and then I’m sure, but I’m considering dealing with it differently this time.

A toilet in a second-floor bathroom in my home overflowed (I’m guessing it became clogged and the flapper valve didn’t shut off appropriately… so I’ll be changing a flapper valve too) and led to water overflowing onto the bathroom floor and, because the floor penetrations were not sealed (😡), into the joist cavity space below.

This bathroom is above my kitchen, and we only realized there was a problem when water started to drip (gush, really) out from around a recessed light fixture in the kitchen ceiling.

So now we have a substantial amount of moisture in the joist cavity, at least several joist bays wide in an area at least 12-15 feet long (I can tell because the water is seeping through the drywall seam; see photo).

The whole assembly will eventually dry, but I am concerned about mold. I’m sure the best, most effective solution would be to tear down the entire kitchen ceiling and re-drywall, but suffice it to say I am not enthusiastic about that prospect; I’d rather spend a day having my teeth drilled than a day mudding drywall.

I’ve considered drilling holes in the drywall in each affected joist bay to try to get some added air flow and aid drying (simple spackling of small drywall holes is easy), or I suppose I could just do nothing and see what happens.

(One person I spoke with suggested turning the heat up in both the bathroom above and the kitchen below to try to aid drying; another person suggested the opposite, keeping the area cool to retard mold growth until the moisture dries.)

I’d be curious everyone’s thoughts here.

(I’m in a pretty moist part of Climate Zone 5A.)

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    Dana Dorsett | | #1

    If there's any way to actively move conditioned space air through the affected joist bays for a day or two that will help even more. Cutting a SINGLE clean hole with a hole saw sized for hose of a shop vac, and setting it up to just run for a day pulling air from the recessed lights through the joist bay would probably do it. Save the plug to make the repair easier.

  2. walta100 | | #2

    As a onetime event I think everything should dry out before mold will grow. Only if you have a slow leak or this happens often would I open things up to speed drying.

    If this toilet is a early low flow design that often clogs or requires double flushing replace it, the new models work much better.


    1. cconti | | #4

      Thanks for the response. Yeah, part of me was thinking the same thing ("Do I really need to open it up? Will this one-time occurrence really create a mold problem?"). I'm really not sure. Cutting holes in the drywall and then having to repair them is certainly a pain that I'd like to avoid unless it's necessary, but at the same time I would really hate to not do it and create a larger problem...

      The toilets in this home (built in 2001, but my wife and I only just bought it about a month ago) have been problematic. Two of the three of them run excessively. We haven't had enough experience here to know if clogging is a significant problem.
      One way or the other, it appears I'm at least going to be replacing the flappers in two of them.

  3. cconti | | #3

    Ah, interesting idea to use the shop vac for *suction,* rather than trying to *push* air through the cavity...!

    Because there aren't any perforations in the drywall on one side of the 'spill' (there are only recessed light cans to the right of the affected area; none to the left) I'm concerned that relying solely on air entering those holes won't dry all the affected joist bays. What I may do then is cut the (single) hose-sized hole you suggest in the center of the area, and drill small, 1/4" or so holes in each affected joist bay at the opposite end of the area to allow air in.

    Do you think enough air would move between joist bays (between the joist and the drywall below, and between the joist and the subfloor above) for the single hose-hole method to work well?

    Thanks for the idea!!

    1. Expert Member
      Dana Dorsett | | #5

      Even if it's not dragging conditioned space air through all of the stud by the will be some amount of turbulence & mixing, and air is EXTREMELY vapor permeable. As long as there isn't somewhat air tight blocking in the stud bay drying out one end will dry out the other. You don't really need to add a second hole, but if you do make it well past the affected area.

      Walter is right that a one-off occurrence won't create an ongoing mold problem destructive to the house or human health, but for those sensitive to mold spores drying it out sooner is better than letting it dry slowly.

  4. walta100 | | #6

    2001 was a bad time to buy a toile. If you plan on staying I think changing them would be the smart move.


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |