Just went to look at a moisture problem and I’m stumped. Installed an asphalt shingle roof on a townhome about 5 years ago. We removed cedar shakes on plywood (the original roof – about 10-12 years old). There is one brick chimney on the common wall that protrudes into the unit in question. It serves a fireplace on the first floor and has a second flue for a furnace. The attic is well vented and has about 8″-10″ of blown cellulose. The chimney is exposed about for about 6 feet inside the attic, but is furred and drywalled on the second floor.
There is a gas furnace in the attic and one in the basement. The attic unit has about 10′ of B vent running to the chimney and is cut into the second flue. The chimney was flashed (on 3 sides) by my guys that flash chimneys every day all day.
Here’s the problem. Nobody lives in the home. It’s used on occasion for a night or two at a time. Mold started showing up on the bedroom ceiling where the chimney passes thru the second floor at sometime. Could have been before the new roof or after. Nobody used that room for a long time. There is a furnace duct about 4′ away from the chimney and it was full of mushroom type growth.
When they discovered this about 6 months ago they called me and I sent the guys that flashed the chimney back and they took the flashing apart, re-installed it and couldn’t really vouch for what the problem was. The owner called again last week and we reflashed the chimney this time.
They called again today and said they’d been in the attic and the chimney was wet. We had a thunderstorm last night and again this morning. I went to inspect it this afternoon (it hadn’t rained in 4-5 hours) and the whole surface (all three sides – 60 sq ft of surface) of the chimney was DRIPPING wet. I have never seen a chimney so saturated and I can’t imagine how so much water could bypass the flashing so evenly. The insulation was soaked about 12″ out from the entire perimeter of the chimney.
I had them turn up the furnace while I was there (it’s about 3′ from the chimney) and I could immediately smell gas exhaust. My 1st thought is the furnace flue is clogged and the exhaust vapor is condensing.
The conditions today were 56 degrees and 100% humidity.
Any thoughts?
I refuse to accept that there are limitations to what we can accomplish. Pete (I am so in love with myself) Draganic
Replies
Is it possible that there is an issue with the chimney cap that is causing the brick to become saturated from the top down? Check out this page, tech note 10b Residential Chimneys, Fig 3. "Chimney Cap Detail".
Is it possible that there is an issue with the chimney cap that is causing the brick to become saturated from the top down?
I'm assuming that you're calling a "cap" what we call a "crown" - the horizontal area of the top of the chimney.
I didn't have what I needed to access the top of the chimney today. We're going back tomorrow to look at the crown and I've seen leaks of this type before, but not totally saturating the whole surface like this.
There are metal flue caps but the crown is mostly exposed. http://grantlogan.net/
I refuse to accept that there are limitations to what we can accomplish. Pete (I am so in love with myself) Draganic
I think you're right, Grant. From your description if the installation, it's gotta be condensation. At least I can't think of anything else that sounds logical.
There's a lot of water vapour in gas-furnace exhaust; combine that with 100% relative environmental humidity and a flue blockage somewhere and you could easily wind up with a wet chimney.
Can you run a snake down the flue to see if there's a bird's nest or tennis ball or something in it?
Dinosaur
How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....
Can you run a snake down the flue to see if there's a bird's nest or tennis ball or something in it?
Furnace guy is coming tomorrow to check the draft on the gas flue. Soon as I prove it's not my flashing, I'm out of it, and the owner is pretty much agreeing it can't be the flashing, but this is puzzling.
Why aren't you on the slopes, man? How's Ryan?http://grantlogan.net/
I refuse to accept that there are limitations to what we can accomplish. Pete (I am so in love with myself) Draganic
Why aren't you on the slopes, man?
I was on 'em all day, punched out at 5:15, changed outta my uniform and went home. I have no-repeat-no desire to be there at 8pm dodging groomers and snowmobiles in the dark. If I wanna go play in the snow at night, I visit the wolves and deer in the woods out behind my place. They are very civilised and shy and respectful, unlike the geeks who sign my paycheck.
Dang it, Grant! I checked in here tonight specifically to get my mind off all the corpo-clone idiot stupidvisors at the mountain who seem to spend all their time telling us to do things wrong just so they can yell at us the next day and order us to undo it all over again.
I spent a lovely 90 minutes getting mid-term performance-reviewed today: Grumpy the Fat Dwarf Boss gave me mega-helpings of verbal shît for an hour an a half as he checked off items on his 3-page-long official evaluation form...and at the end of that time he looked at the scores he'd given me (the lowest he could possibly get away with) and said, well, according to this, you're doing a fine job.
I said, 'Congratulations, Porky, you have just won the Nobel Prize for De-motivation.'
How's Ryan?
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Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
I think it's the cap (Crown) also. The joint around the outside of the flue is the usual culprit. I just moved into a new house this fall and have the same problem. Well not the mold, but when it rains hard the
Face of my fireplace is visibly wet. These caps are one of those building details that somehow get no attention.
If they are significantly lowering the temp while the house is unoccupied, they are creating an ideal environment for condensation.
Also, combustion appliances on different floors are not supposed to share a flue - which probably isn't related to the problem, but could be
May your whole life become a response to the truth that you've always been loved, you are loved and you always will be loved" Rob Bell, Nooma, "Bullhorn"
"We Live" http://www.youtube.com/watch?v=7kuBgh0VCqI&mode=related&search
And Annie Ross's "Twisted" http://www.youtube.com/watch?v=8lqivrCIRGo&mode=related&search=
If they are significantly lowering the temp while the house is unoccupied, they are creating an ideal environment for condensation.
Aha - the attic furnace was turned off ( I think - it as colder in the house than outside) and the basement furnace was set very low. They are not in the same flue. The basement furnace goes thru a wall termination. But, there is a thimble in the basement for the furnace flue (the one that the attic furnace is vented thru) and it's standing open.http://grantlogan.net/
I refuse to accept that there are limitations to what we can accomplish. Pete (I am so in love with myself) Draganic
You have at least in some measure, rain water penetrating the brick chimney. Brick masonry, especially chimneys, isn't water proof.
Treat the exterior with a silane-type or siloxane-type water repellent (not a 'sealer')
Jeff
Gas exhaust condensing should actually run down the inside of the flue to the bottom of the chimney.(assuming this chimney has a flue liner in it.) Although I suppose it is possible that the vent is plugged for some reason prior to entering the flue.
Birds nest / Squirrel?
I would bet on water penetrating the brick , mortar joints or cap above the roof line.
I'm a chimney sweep, have been for close to thirty years. I think you are on the right trail with regard to condensation. It may be because of obstruction or oversizing of the flue. I would suggest you contact a Chimney Safety Institute certified sweep. You can find one in your area by going to csia.org. Good luck.
Thanks for the info.
I've long since solved the problem by putting a full chimney cover on. Water was infiltrating the crown which was mortar.
I used to be a certified sweep - 25 years ago.http://www.quittintime.com/ View Image