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Question DetailsAsked on 2/11/2014

Water stain on the ceiling

We noticed this water stain a while ago, and it seems to get worse recently. This is first floor ceiling of two story colonial. Above the ceiling is the exhaust venting pipe of first floor bath, towards the side of the house. So basically there should not be any water in the pipe. So when I saw the stain first time, my response was to look at the vent cover and re-caulk around it. But this stain seems to grow recently.

We live in Massachusetts, and the roof is covered with snow, and I am not sure if this might be the source of the water. However, I am very puzzled about how water get into the house. Any thought is welcomed. Thanks.

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9 Answers


Answered 6 years ago by shiyang100


Water leaks can be tough to find their source. They are not always directly inline where you see the damage.

Here are a few thought that could be happening.

As the snow melts around the vent because of heatloss the water will flow down the pitch of the roof. As the water moves away from the vent it will freeze. As this cycle continues the ice will form a dam . As more water flows and hits the ice dam it will back up and can flow into the vent pipe and into the house. If the vent pipe has a hole or is not properly sealed it will leak out onto the topside of the ceiling causing a visible water stain on the inside.

This could also be caused by condensation in the same pipe. As the hot moist air from showering or the naturally humid air excapes the vent it will cool and condence before it has time to exit to the outside. Water droplet will form and flow back down the vent pipe. It is like a glass of ice water. The outside of the glass will get wet. The glass isn't leaking but rather condensation is developing.

Another thought is that if there is a bathroom directly above where the water stain is, there could be a leak in the plumbing drain or the toilet needs a new wax seal.

If you can find an inspector that does Thermal Imaging he might be able to find the source of the leak.

Hopes this helps.


Answered 6 years ago by Homefront Inspection


Regardless of the cause, and could be any of ones other comment stated, I would not let it go in case there is enough water up there to rot the floor joists. Rather than spend money on a thermal scan, which will not give you a lot of fine definition, I would just visually inspect it.

A COLOR (B&W does not show water and staining well enough) fiber optic camera rents for from $15-25/day at a tool rental place or some auto supply stores; costs about $75 from Amazon or Harbor Freight or equal. Takes about a 1/2" hole to feed it up in and take a look around - should show pretty quick where the water is pooling on the drywall, and where it is coming from.

Another alternative, if you can see in the outlet of the duct on the side of the house (ladder job), sine a BRIGHT (6V lantern type best) flashlight in the duct and see if it is frosted inside - if so, likely the cause.

My initial guess, like - who was it - Don - is condensation in the exhaust line, especially if this occurred only during unusually cold weather. If you run the fan for only a few minutes the moist air going up the duct condenses on the inside of the cold duct, then runs down the duct till it either comes out at the fan, or at the first joint if the joints were assembled with the lower section inserted inside the higher ones so the joint catches the drips and it leaks out the joint. Solution is insulating the duct (they make slip-on and wrap-around fiberglass insulation specificdally sized in tubes for exhaust duct), and also run the fan for 10 minutes or longer at a time so it heats the duct above condensation temperature, then evaporates the condensation that formed when the air first started contacting the metal.

Answered 6 years ago by LCD


Thanks so much for the answers. I forget to mention the first floor bath is half bath, so high humidity might not be the case. does this make difference?

Answered 6 years ago by shiyang100


1) You are right - that does make it a lot less likely to be condensation - you would have to have very high house humidity and very short fan run times to build up noticeable moisture in the duct in that case.

2) When you said duct pipe is toward side of house - I presumed that meant it exists out the side of the house, not up through the roof. PSignificant water is pretty unlikely to be coming in side of house, even if leaking around duct exit - would likely not be enough to get to the drywall - would usuallyk run down the outside or inside of the wall and evaporate there. If duct might turn and go up through the attic - then much more likely to be a roof jack (roof seal) or vent hood leak, or possibly condensation though not nearly as likely.

3) I would say check in the attic (if you have access) for any signs of water leakage, and also go around the outside of the house with a strong flashlight (6V lantern type if possible - MUCH brighter) - and ideally with a ladder getting right up under the eaves so you can see into the attic there too - and look and feel (watch for roofing nails sticking through) for any signs of heavy frosting, water running down the outside of pipe or vent penetrations through the roof, staining or wetness on the bottom of the roof or in the insulation in the attic, ice damming at the roof edge that is backing up water that is coming down through the roof sheathing near the wall and dripping down at the wall. If you have been having real cold weather, a light frost haze on the roof sheathing, especially if uniform throughout the attic, is not unusual or likely to be the cause of this. Heavy frost, or frost melt drips wetting insulation in that area, yes.

4) Commonly, melting frost or leaks in the roof will run down the underside of the sheathing or rafters - especially on 4:12 pitch and steeper roofs - and then drip off at some point - at a rough spotor splinter or open knot in the sheathing, at a pipe or duct that happens to be in its flow path, upon hitting eave airflow troughs (the cardboard or plastic troughs that hold an airspace open over the insulation at the eaves), at bug screening at the eaves, a nail poking through, etc - any place that stops its flow along the underside of the sheathing or provides a more direct way to flow downwards and is enough to interrupt the surface tension that is causing it to follow the bottom of the sheathing. Sometimes drops off along the way, sometimes makes it all the way to the back side of the fascia board.

5) Also - while in attic- make sure all vent pipes actually go up through the roof to vent hoods or exhaust caps - a LOT of contractors don't coordinate their subcontractor work well on this matter, so the fan installer puts in the bathroom or kitchen fan and runs the duct almost up to the roof but does not drill the hole in the roof sheathing for it to avoid rain entry before the roofing is on, expecting the roofer to connect up to the roof vent hood when it is installed - then the roofer comes along and drills the hole (or not) and lays down the roofing and installs the vent hood expecting someone else to connect into it, so you end up with all the exhaust air going directly into the attic, resulting in condensation in the insulation and frosting on the underside of the roof in cold weather - I have seen up to 2 feet or frost on the underside of roofs in very cold areas. A bit of warming, the frost melts, and drips down one or more places - wetting the insulation if a light frost, but soaking the insulation and flowing on through to the underlying walls or ceiling if real heavy - particularly after a rapid thaw that melts it faster than it can evaporate and be carried out by the attic ventilation.

6) If you see no source there, then I would go with the fiber optic inspection camera - BTW - to avoid having to open up a big enough cailing hole for a flashlight, you will need one with a bright enough built in fiber optic lights (preferably two bulb type) to be able to see up in the floor space.

7) If you are not up to this yourself then a roofer could check the roof and attic, and might be willing to open up the ceiling to inspect there too - though would be very unlikely to have a fiber optic camera, so unless you specify he rent one and bring it with him, he would open about a 1-2 foot hole in the ceiling, which will be too big to repair with spackle so will require a drywall contractor and painter for repairs once job is all done. The advantage of the fiber optic scope is the inspection hole in only 1/2" or so, allowing you to fix it yourself with spackle and touchup paint.

8) BTW - digital inspection camera looks like this, in case I did not already give you that -

9) Other possibilities - an upstairs bathroom leak (though usually shows up near center low point of ceiling or along interior walls), baseboard or steam heating pipe leak (almost all piping runs along the outer wall), leak at window flashing running down in and escaping from the wall at the upstairs flooring sheathing, then down into the downstairs ceiling, etc. Run your fingers in along the base of the upstairs wall for about a 5-6 foot width above the leak area, trying to get in under the basebaord if possible (watching out for nails sticking out and carpet nail strips) and feel for any moisture, and smell if any mildew smell. Also check along any exposed heating system piping above the stain area for wetness, and look for "bloom" - mineral buildup on the pipe due to a leak, usually at joints - typically green (on copper pipe), reddish (on steel pipes), or white or yellowish (on any type pipe) - caused by mineral deposition as the leaking water evaporates, just like the travertine mineral buildup around the Yellowstone hot springs.

Good luck, and may it be a minor, easy to fix problem.

Answered 6 years ago by LCD


Half bath won't generate any humidity at a level to create sweating.

What is above the bathroom on the second floor?

Answered 6 years ago by WoWHomeSolutions


I have been spending some time this morning looking around. I have completely no idea where water is from.

Above the water stain is the second floor hallway, and both bathrooms are almost 20 ft away. Also on the left hand side of water stain on the second floor is a window in the hallway. Everything seems to be fine with the window. I went up to the attic, there are no sign of water. I am kind of desperated now trying to find out what happened. I even have no idea which type of contrator to start with. Just seeing water stain is growing.

Answered 6 years ago by shiyang100


Sounds very perplexing to say the least.

If you don't see water in the attic, the next likely culprit is the window/siding.

Any pictures?

Answered 6 years ago by Davidhughes


Sounds to me like time to inspect in the ceiling area to start tracking the cause.

Could well be from outside leakage coming it for damaged siding or window flashing, but if you looked and saw nothing there (especially along top and sides of window frame flashing), then maybe you have a pipe running through that area that has developed a leak - maybe running to bathrooms or kitchen or an outdoor faucet ?

Answered 6 years ago by LCD

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