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Question DetailsAsked on 1/10/2016

We are looking for help diagnosing and repairing a small but persistent water stain on the ceiling

We are looking for help diagnosing and repairing a small but persistent water stain on the ceiling of the kids' first-floor bedroom and around an outlet in the second story master bedroom. The first floor water stain is around a nail/screw in the stud. The stud in the first floor bedroom runs along the second story outside wall. The second floor outlet is on the outside wall above the stud. We just discovered that stain.

We've had the drywall on the first floor cut out and replaced, but the stain has reappeared. In the attic, we don't really find any evidence of water incursion and no mold. We had extra insulation added. But, the stain on the first floor ceiling has reappeared.

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Voted Best Answer

I am going to assume these are one above the other - not unrelated areas.

Too bad when the drywall was cut out you did not have the leak traced up into the wall, using a fiber optic scope or cutting into the drywall every couple of feet to trace back to the source visually (staining) and by hand (wetness).

Take a look at possible sources - siding defects, situated under window that might have leaking seals or flashing/trim, ice damming causing a roof leak right over the wall, roof leak or melting frost dripping along underside of sheathing till it reaches the outear wall or bug screenign then running down that into the wall, maybe a roof leak elsewhere in the attic where the water is dropping to the top of the ceiling drywall and flowing along the top of the vapor barrier to the edge of the ceiling and then into the wall, leaking attic A/C evaporator pan, condensation leaking out of fan ducts (cold weather) or A/C ducts (warm weather), etc.

With just a stain but no surface wetness detected, using thermal infrared might or might not pick it up. You could have a home inspector or energy auditor with a thermal infrared camera come after a rain and see if he can pick up a wet zone, especially in exterior wall insulation.

You may be able to download an App (or call up the capability built-in in many modern Apple iPhones and tablets and some digital cameras) to recalibrate the camera so it "sees" wall temps better in the near-infrared - can work quite well in some cases, though not as precise as a true thermal IR camera. You can also rent a thermal IR camera for $40/70 range (half/full day) at home Depot or $50-100/day range at tool rental places - try it after a good long rain so if from rain (highly likely) it will be wet, which shows up as a warm/cold spot in the wall from the outside (heating/AC seasons respectively) or as a cold/warm spot in cold/warm weather respectively as seen from the outside. You can see sample videos on Youtube and at (major manufacturer of such scanners and cameras).

You can also drill small holes about 1/2" diameter and use a fiber optic scope/camera to look in uninsulated walls for staining (color WAYYY better than B&W) - or in outer/insulated walls drill about 3/16 - 1/4" holes and use a plant moisture meter to detect moisture in the insulation. Small holes way easier to patch than hand-sized eyeball inspection holes.

To have someone do the investigation for you - because they are not selling a service other than the investigation and have no incentive to tear out more than needed because they will not be doing the repair, home inspector or energy auditor would be my choice to do it - one who has a thermal IR camera. Probably $100 bare minimum, maybe up to about $200-250 if hard to trace or obscure source.

I would start the search at the upstairs outlet - leak has to be above or only slightly below that level, if same leak is causing both stains.

Answered 4 years ago by LCD

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