Hello all. I live in the Northeast and recently came across a roof issue that I’d like to throw out there. I looked at a house with a 3/12 roof pitch that had a solid roof insulation system: 2″ celotex layed directly on top of a T & G cedar roof deck, with an air space & then sheathing & shingles. There is a center chimney at the ridge made of cement bricks that bleed in the hot summer months inside, but don’t necessarily leak during rainstorms. The condition is less frequent in the winter months when the temperature is cooler. The original roofer says that it is the chimney causing the problem, but when I inspected it, it actually looks to be in pretty good shape and flashed correctly. There are also ridge vents and ventilated drip edge on the eaves. My thought is that the roof venting is causing moisture buildup and condensing on the cold cement bicks in the warmer weather as the warm air rises up and meets the cooler cement brick. I doubt there was any provisions made to divert the warm air around the chimney to vent out the ridge vent, and that causes the interior brick to appear to be sweating in the house. Since the air draw would be relatively slow on a flat pitch like that, I think that warm air condenses on the cold brick, is drawn into the brick, and sweats inside. The problem is almost non existent in the cooler weather, maybe less temperature difference eliminates the condensation. Would appreciate thoughts from any experienced roofers or masonry pros.
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"that bleed in the hot summer months"
Clear moisture or tar like gunk?
My thought is that the roof venting is causing moisture buildup and condensing on the cold cement bicks in the warmer weather
You are referring to the air in the "air space" as being the culprit right?
You might have hit the nail on the head. But....Some things to consider.....
How much of a gap is this "air space"?
Does it run continuously from the soffit to the ridge?
Do you see drips or runs of "sweat" on the OUTSIDE of the chimney, directly below the cedar decking INSIDE the home?
Does the chimney "sweat" on all four sides, or only on the "downhill" sides where the air would end up against the block?
The water isn't drips, it's more like soaked into the cement brick & sweating out once inside. As far as the vent, I believe it's 3/4" -1" max. and the sweating is only on the downhill side of the chimney, which leads me to believe it wasn't vented around the chimney, instead up to it. I can't imagine the chimney flashing is the culprit as it doesn't leak or sweat during rain or snow.
Also the flashing would tend to fail on the uphill side, not the downhill where the water is running away from it. Since it only happens on the downhill side, I would suspect the venting problem too, but.......condensation is mostly a surface condition, so I would have expected to see some "runs" on the surface of the chimney, not a "bleeding" from the blocks themselves......Hummmmmmmm
Is the decking tight to the chimney on the interior of the room (downhill side)? Caulked? Stained? I would exoect some staining on the decking at this location from the moisture soaking into it (LIke a wet coaster w/ a glass full of condensation in it).
Condensation (cool, heavy water droplets) would run down the chimney face to the decking, then down the decking (which slopes) before soaking into the wall. If there is NO sign of staining or surface moisture at the chimney/decking (on the downhill side) juncture, you either have a "waterproof" seal there, or you problem is elsewhere. Check it out.
pickings, I appreciate your help here. The other thing I forgot to mention was that the chimney is a centerline ridge chinmey of fairly ggod size, 7'-8" wide by 32". Centered directly on the ridge. There is also a copper chimney pan that was installed on the course of brick directly above the lead flashing so that on the exterior, there are no exposed cement brick from the pan down & above the pan, the chimney was rebuilt with new clay brick. There are weep holes at the pan level in the event that the chimney above does soak up some water & filter down in the brick holes, & it can drain out. I can't imagine that amount of water could have somehow gotten through the pan. The interior decking where it meets the chimney does have some staining, not alot, but some, and they occasionally get a small drip a few feet away. The decking is fairly tight to the chimney, as it is exposed on the interior, but from the inside anyway, doesn't appear to be sealed or caulked. The thing that confuses me is the issue that the bricks appear wet when it's hot & sunny out more so than bad stormy weather. The only other thing that would make sense to me is possibly water blowing into a ridge vent because of the shallow pitch, but why would it show on the long side of the chimney where the ridge vent isn't, and not when it's raining more than sunny? I know water is a funny thing , but this one has me a little baffled
Edited 12/2/2005 10:56 am ET by VT.lab
Sorry for the delay, I don't visit every day.
Tough one here...But....Does it happen on BOTH downhill sides? If so, it might be water from the bricks above filtering down, or condensation.
If not, and it only occurs on one side, I would suspect a leak. Here's why...
and they occasionally get a small drip a few feet away
Could be a small roof leak (near said drip) which allows water to accumulate in the air space in that location only? It may or may not drip through, but on hot days, the moisture would evaporate and travel up the airspace to condense on the cooler blocks.
Just a thought.
pickings, thanks man, I appreciate your help, this is one of the more puzzling things I've dealt with in a while. They do get water on both sides. I also thought the water may be filtering down through the cap & bricks, but the top section above the lead flashing has been rebuilt and a solid copper chimney pan installed.
You may have something there though about the small leak, where the water may blow into the ridge vent and then condense in the airspace and on the bricks in the warm weather. I didn't do this roof , so I don't know how the airspace was vented. I was just lucky enough to be the guy trying to figure out the cause
I have resigned myself to recommending to the owner that the roof around the chimney may need to be pulled up so I can better see what's going on. I may be opening up a big can of worms here & not sure that I want to get involved in fixing someone else's potential mess
Thanks for your help though, & if I get it figured out , I'll get back to you
I may be opening up a big can of worms here
Good luck.
Just remember......you can always go fishing.
It sounds like the moisture is inside the block cavity and bleeding out, its either rising in the blocks from below, humid air, condensation, or leaking in from the cap at the top, check that the chimney top is well parged and sloped out, and that the flues are capped .. if the later, consider a metal cap to cover the blocks, if the former maybe you could alleviate it somewhat by drilling some upwards sloping holes into the cavity of the blocks at the top of the chimney .. its a mystery ..