Condensation 101?


#1

Hi, I need some help with this one:

I’ve got a post and beam ranch style home with vaulted ceilings. There are three main beams (one ridge, two mid on either side) running the length of the house with rafters on top. From inside out the roof over the vaulted area is drywall (nailed to the bottom of th rafters and between the beams), plastic vapor barrier, styrofoam block insulation, 1 3/4" air gap, 3/4" plywood deck, paper & shield and shingles. There is finish trim nailed at all points where the drywall meets the beams. The plastic vapor barrier stops right at each beam as well so it makes a good place for condensation to exit the roof system without ruining the drywall. There is a continuous soffit vent and continuous ridge vent except for 32" where their is adjacent skylights on either side of the ridge above the chimney. The chimney is midway up the roof. Had a new roof (tamko asphalt shingles) put on in August.

Started having drips the length of the mid beam on the side of the house with the vaulted ceiling when it snows but nothing from rain, not even during torrential downpour. The roofer claims that it is condensation and not his problem, which does make sense (the condensation). The air is 65 deg. F, the humidity is 33%, so the dewpoint should be approximately 35 deg. F.

I used a thermal scanner with picture overlay on the roof. There are hot spots around the chimney flashing, skylights, and the gap between two sets of rafters appear to be 7 degrees hotter than the rest. I measured the rafters and checked below. There is recessed lighting in those two sets of rafters. I pulled the cans and they are not sealed. There was one or two nails with condensation behind each can but it was by no means wet in those rafters while at the same time I had drips coming down along the mid beam just below the lights and a few feet away laterally. The thermal image shows the heat starting at the lowest light and exiting the ridge as it should so I’m guessing the airflow is adequate in at least those two rafters to not be the source.

The roof overhangs on each end. On one of the overhangs there is also water running down the soffit (not sure if its called soffit on the overhang at the end but don’t have a better term for it) just below the ridge beam. It seems odd to have leaks there because there is at least one joist between the leak and the exterior wall of the house. It is almost like the ridge is not allowing the air out at that joist.

I’m at a loss as to what could be the source of the condensation on the midbeam other than maybe the chimney since the laminated beam that is dripping runs through the edge of the chimney. Without tearing out a lot of ceiling drywall I’m not sure if they put any type of cross ventillation on the rafters below and between the chimney and skylight as those would be dead air spaces. Additionally, the drips are coming down 25’ in either direction of the chimney and based on my 4’ level at the ends the water would have to defy gravity for the chimney to be the source.

I’ve called some other roofers and contractors to come give second opinions but was wondering if any of you have come across something like this before? If so I’m open to any ideas to remedy the situation.


#2

First off is this a catheral ceiling? If so are there baffles installed? If not thats one problem. Insulation is your main problem. Its the lack of it that is normally the problem. SInce there is not alot of roof going with a spray insulation with a high R value would fix it but you would have to remove all the drywall. Did you put new windows in the home? You said can do you have can vents on the roof also to go along with the ridge vent? Email or post some pictures of the room so i can get an idea of whats going on. Please answer my questions. Yes i have seen attics rain like a rain forest before.


#3

I’ll try to attach some pics after work today. The cans that I was referring to were the cans for the recessed lighting. They had mount holes in them and were not the sealed type.

I forgot to post some other info. I have electric heat, and the insulation is 6-8" thick. I’ve never seen blocks of styrofoam used as insulation before and am not sure what type of R value it will provide.

You mentioned spray insulation as a possible solution. Once the drywall, vapor barrier, and insulation is removed would they be spraying the underside of the roof deck? Would I have to use another type of insulation instead of the styrofoam when it’s put back together?

I’m not sure whether this is a cathedral ceiling or not but hopefully the pictures will help. Thanks.


#4

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No new windows were put in, they are original from 1979. There are no baffles that I could see. The first roofer that came by today referred me to a spray in insulation guy too. Any idea what I should be looking for from them?


#5

You need a cold roof.
Another roof built over your existing roof with an airspace for ventilation.
You can also add insulation when you do this.


#6

Yea axiom your right i forgot about that. It is the best way to do ir if installed correctly.


#7

That is one horrible looking flashing job!

I am replaceing an 7 year old roof right now that has catherdral ceilings with no baffles. Tear off shingles, plywood, install baffles, new plywood, new shingles. Too Bad!


#8

Axiom is right on that. It will be the most effictive and long term solution to your problem. It will also be the most expensive.


#9

I could be wrong but from what I read in his original post what your recommending has already been done

It looks like the majority of the venting is clogged with snow and ice which could contribute to the problem.

I have a feeling though your problem is at the chimney, from the pics it appears they used the old one piece flashing instead of cutting it back off the roof and putting in new step flashing and using the old as counter flashing instead of as the roof flashing it appears to be. With those gaps it wouldn’t take much to create a small ice dam below the gap of the flashing that would force any melt water in the area back into the gap between the chimney and decking. Since that rafter runs into the chimney this is the first thing I would look at trying unless you can locate another more likely source.

If that’s the case it’s a simple repair, remove the shingles around the chimney, trim the old counter flashing about 1/2" above the roof line then lay in Ice and water barrier around and up the sides of the chimney then reinstall the shingles with new step flashing.


#10

When the house was originally built the styrofoam insulation was laid right up against the roof deck (sandwiched tight between the drywall, vapor barrier and deck). As the story goes the roof didn’t make it two years before they had the builder come back and tear the roof off, and create the air gap and run a continuous vent along the soffit on both sides of the house. I had an insulation rep there today and he noticed that they had nailed furring strips under the rafter, then attached the vapor barrier to the furring strips. This allowed them to drop the insulation blocks down about 1 3/4" inches to create the air gap. He thinks that because the insulation is not tight to the rafters (side gap) that I am getting a lot of heat loss. He also thought that the recessed lights were a big mistake.

What I don’t get is why is one rafter with recessed lights so much hotter than the other. The ridge above that rafter run is the hottest spot on the roof. It’s like there is no ventillation out of the ridge at that point and the hot air is trapped under the cap shingles.

The cold roof sounds like the most efficient but I am concerned that my framing might not support it. The roofer that put the roof on in the pictures said that the rafters are installed at their max allowable span. With the past moisture he had concerns about their load bearing capability. That being said we just had a three inch snow load and my fat ass up there with no collapse.

What is the best way to inspect for chimney leaks? As you can see the flashing is turned up at the bottom as are some of the shingles. Is that normal? Do I have to remove drywall underneath to inspect properly?

If my structure will not support a cold roof what should I look for from an insulation job. They ran 3 options by me but haven’t given me a recommendation until there guru comes out (worse than they thought it would be).

Option 1 was to tear out everything non structural below the roof deck and spray insulation on the underside. They didn’t explain if baffles would be installed and if I would still need the soffit and ridge venting.

Option 2 was to remove the drywall and vapor barrior and re insulate what is there and fill the voids but not interfere with the air gap. I would then have to replace the vapor barrier and drywall.

Option 3 was to solid fill the roof by removing strips of drywall at points working up the ceiling from bottom to top and flooding the voids and air gap with liquid foam. BY spraying through the air gap. They would also block and fill the soffit basically making a solid insulation filled roof with no interior ventillation. I’ve read about that with church roofs with slate on top but would something like that work here?

I really appreciate all of you taking the time to give your input. Thanks a lot.


#11

you could remove the drywall around the chimney but if you don’t have spotting there that may not let you see the leak. If the water is traveling the beam the source could be above that and out of view other then from above. Personally what I would do is remove the shingles around the chimney and if there is a leak there it should be able to be spotted. If that’s the case proper flashing could be all you need to fix the problem. Since this would be the least costly option I would try that first. If I’m wrong it could cost a couple hundred dollars to find it out, if I’m right it could save you a good bit.

Basically I would make sure I knew the source of the moisture before commiting to a large investment that may or may not elimnate the problem. I know I wouldn’t want to spend 2 grand then have the problem reappear in a year or two.

The shingles and flashing around the chimney should be flat and not sticking up like that, that’s one reason I suspect the chimney may be the source of the problem. The other is looking at the flashing it appears to be severly corroded near the bottom and if they didn’t install new step flashing probably has holes at or near the bend of the metel onto the roof deck. With those things and the beam running into the chimney would make me look there first.


#12

If youre going to do this once and for all, I would remove the roofing, decking, insulation, vapor retarder, insulate to the drywall with closed cell insulation (leaving an airflow gap, then put a deck on and roof it.

Probably the most economical long term solution.


#13

Hi Bucket full of rain,

I have a few questions. How long have you lived in the house? Was the roof that was just removed leaking in the same way?

You mentioned that they installed felt and shield. Do you mean ice and water shield along the eaves and then felt the rest of the way to the ridge?

If I was on site, I would do a thorough assessment before I offered an opinion, but my hunch is that the most recent roofers covered the slot of the ridge vent with underlayment.

At any rate I wouldn’t be so quick to let the roofer that installed this roof off the hook so easily. Either the roof was leaking before and he did nothing to correct the defect or he installed a new defect.


#14

Vince,

I’ve live in the house since August, which is when I had the roof put on. There are signs the either the roof was leaking or that there was a condensation problem when I bought it (all the beams had drip marks, yet only one is dripping now). The home inspector recommended a roofer look at it and tell me what it needs, but that it definitely needed replacement and/or insulation.

The roofer felt the insulation was fine. He found one or two sections where the soffit vent had been obstructed. He found evidence where they had at one time lowered the insulation to make the air gap below the deck.

You were right about what I meant about felt paper and ice and water shield. I know that both types were used but did not see where he put which type. I’ve questioned his work on the ridge. He supposedly called the ridge vent manufacturer’s rep to come and look at it but the rep is not returning his call (for over a month now). I’m getting the run around, but I’m afraid that if I lifted the ridge he’d accuse me of causing the problem. I brought another roofer out (impartial third party) but there was too much snow & ice and he didn’t want to risk his neck up there until the roof had cleared. I hope to have a 2nd and 3rd opinion soon and I definitely want a professional on site opinion about the flashing after all the criticism it has brought.

Something else for everyone else who has been reading this post. I’m having drywall seams start to show through and/or crack at various points on the ceiling on the front and back side of the house now (not just along the one beam anymore). It seems like a more widespread issue than I first thought. I was told that these seam cracks were further evidence that it is a condensation problem but am not dismissing a problem with the chimney flashing (could have multiple issues to deal with).

Thanks again. Keep the suggestions coming, it is much appreciated.


#15

what about blowing or forcing air or smoke through the soffit vents and see if it comes out the ridge vents. I really think that there is not sufficient air flow and not enough r value in the ceiling insulation. All the heat in the room is up in the ceiling and I believe that there are areas in the ceiling that are allowing heat to reach the underside of the roof deck and therefore condense and create moisture. The inside of the ceiling may need to be removed and reframed lower to allow for thicker ceiling insulation. It may be necessary to cover the exposed wood beams to achieve a thicker ceiling; but you could always apply a new piece of one by to the face of the drywall directly in line with the original beams. This will give you the exposed beam look that you probably want to maintain.That chimney flashing should also be corrected.


#16

[quote="-Axiom-"]You need a cold roof.
Another roof built over your existing roof with an airspace for ventilation.
You can also add insulation when you do this.[/quote]

That’ll work, or a ventilated nail-base such as the AC foam crossvent, by Atlas, will also work. That’s what we’ll typically do in these situations. atlasroofing.com/pages/Speci … ilbase.asp


#17

[quote=“bucket full of rain”]Hi, I need some help with this one:

I’ve got a post and beam ranch style home with vaulted ceilings. There are three main beams (one ridge, two mid on either side) running the length of the house with rafters on top. From inside out the roof over the vaulted area is drywall (nailed to the bottom of th rafters and between the beams), plastic vapor barrier, styrofoam block insulation, 1 3/4" air gap, 3/4" plywood deck, paper & shield and shingles. There is finish trim nailed at all points where the drywall meets the beams. The plastic vapor barrier stops right at each beam as well so it makes a good place for condensation to exit the roof system without ruining the drywall. There is a continuous soffit vent and continuous ridge vent except for 32" where their is adjacent skylights on either side of the ridge above the chimney. The chimney is midway up the roof. Had a new roof (tamko asphalt shingles) put on in August.

Started having drips the length of the mid beam on the side of the house with the vaulted ceiling when it snows but nothing from rain, not even during torrential downpour. The roofer claims that it is condensation and not his problem, which does make sense (the condensation). The air is 65 deg. F, the humidity is 33%, so the dewpoint should be approximately 35 deg. F.

I used a thermal scanner with picture overlay on the roof. There are hot spots around the chimney flashing, skylights, and the gap between two sets of rafters appear to be 7 degrees hotter than the rest. I measured the rafters and checked below. There is recessed lighting in those two sets of rafters. I pulled the cans and they are not sealed. There was one or two nails with condensation behind each can but it was by no means wet in those rafters while at the same time I had drips coming down along the mid beam just below the lights and a few feet away laterally. The thermal image shows the heat starting at the lowest light and exiting the ridge as it should so I’m guessing the airflow is adequate in at least those two rafters to not be the source.

The roof overhangs on each end. On one of the overhangs there is also water running down the soffit (not sure if its called soffit on the overhang at the end but don’t have a better term for it) just below the ridge beam. It seems odd to have leaks there because there is at least one joist between the leak and the exterior wall of the house. It is almost like the ridge is not allowing the air out at that joist.

I’m at a loss as to what could be the source of the condensation on the midbeam other than maybe the chimney since the laminated beam that is dripping runs through the edge of the chimney. Without tearing out a lot of ceiling drywall I’m not sure if they put any type of cross ventillation on the rafters below and between the chimney and skylight as those would be dead air spaces. Additionally, the drips are coming down 25’ in either direction of the chimney and based on my 4’ level at the ends the water would have to defy gravity for the chimney to be the source.

I’ve called some other roofers and contractors to come give second opinions but was wondering if any of you have come across something like this before? If so I’m open to any ideas to remedy the situation.[/quote]


#18

I thought all of you yankees knew snow will blow under shingle/over ridge vent…It’s melting on the main ridge beam


#19

I know this is an old thread but in case you still get emails for it, I have a similar issue, so did you fix your problem? Thanks.


#20

Yes we took the roof off, removed the old insulation, installed new insulation, and a 2" vent channel under the roof deck that extended from the soffit vent to the ridge vent.