Condensation in cathedral ceiling - need pro advice


#1

Hey everyone, First the back story, I am in new england, my house has a ~3/12 pitch and the previous owners thought they were being smart by converting it from a tar and gravel roof to an architectural shingle roof, but the pitch is too flat and the water was completely soaking and pouring through in less than 5 years.


So we decided to go with a standing seam roof. When we opened it up we found extensive damage from moisture (we live on a lake) because their were vents in the soffits but not at the top/ridge. The roof is slightly complicated because the main part is a 4-sided pyramid with a giant skylight in the middle so there is no ridge vents anywhere around there. In some cases the rafters had completely rotted away at the top, presumably from trapped moisture:

The only places the rafters were still solid was where they weren’t connected to the vented soffits, such as in the valley and above skylights. So after seeing that empirical evidence and researching it I decided to convert the entire roof to a sealed cathedral ceiling (interior has a cedar over plywood cathedral ceiling on most of the house and drywall ceiling attached directly to the rafters in the most problematic place).

So I ripped out the old soffits and block insulated and spray foamed all the gaps between the rafters:

And the new roof was installed:








Now, 3 summers later, for the first time, I am getting drips from some of the recessed lights and the top door moulding on the wall, and this is on humid days (basically all of July here), more than a week after the last rain storm. We don’t have air conditioning so I didn’t think the inside could be getting cold enough that it could cause condensation, but I have no other explanation for where the water is coming from. I double checked and recaulked any possible seams in the roof above that spot but it continues, again no where near a rain storm. The area where it is is dripping from most is fully insulated, then has plastic vapor barrier attached to the bottom of the rafters, and then drywall on that. I pulled out the recessed light (old-work, not air-tight) and the insulation feels soaked and water could literally be wrung out of it. Seems like more of the water runs down the vapor barrier to the wall and is making the drywall bubble a bit.




If this is a condensation problem, which everything so far points to, then what are my options without ripping off the whole roof and putting baffles and soffit/ridge vents? I could pop off the ridge cap pretty easily and cut a vent into the top of the decking along the ridge beam and at least add a top side vent. Or do i need to pull down the drywall and re-insulate/sprayfoam the bottom of the roof deck? Thanks for your help.


#2

That looks like a good amount of water coming out above the door. I would check very through my for a leak before thinking it is condensation.

The only way to vent that roof the way it is would be hip vents. They could be installed without Removing the roof, but would not do Much without baffles and would not be my first choice on a 3/12.

With the ceiling completely insulated, the standing seam should have been installed on battons installed on top of the decking creating an air space under it and a cold roof.


#3

Should have installed the metal on top of lath (horizontal on top of vertical) and the a vented ridge and hips, or “turtle” vents on the hipped sections.


#4

Thanks for the quick replies. After reading about battens more you guys are probably right, but this blog post seems to suggest the opposite (I think it contradicts itself though): https://canadianmetalroofing.ca/metal-roofing-decking-battens-underlayment/

What do I do about it now? Drill all the rivets, pop off and unscrew the panels, then to install battens underneath? The roof was installed by union corrugated, through Lowes, but the “installation” warranty was only 1 year.

This video looks like they are using the exact same product I have (using same terms too, like z-bars, butyl tape, cleats etc.) and it is installed on battens (only horizontal though): https://www.youtube.com/watch?v=8XSyXCTTfpQ

Also by the way, we had torrential down pours last night, and woke up to it being dry as a bone again. The dripping also only seems to start in the evening.


#5

We’ve done repairs on “snap lock” roofs, It’s possible to remove and then replace panels but a PITA. You will likely have to source and install new drip edge and rake trim due to the added heigth of the lath.


#6

Would spray foaming the underside of the roof deck work too? That way I would get rid of all the air pockets between the drywall and the decking. I think replacing the drywall on the ceiling in the rooms where this is an issue would probably be easier than tearing off the roof.


#7

Every single roof we’ve done that had foam directly against the sheathing (spray foam, batts, or board insul) had significant water damage from sweating.


#8

Can’t agree with rooferman enough. Would not recomend spray foam. Defently not the fix all the insulation guys and green building guys say it is. Once it is in and you still have a moisture problem, you now have mold and wet foam glueing everything together.


#9

The remedy is simple and the problem is moisture precipitation forming on the underside of the metal roof when the differential from the two sides is greatest.
The vapour barrier, foil, fortecon call, it what you will, needs to be AGAINST the roof sheeting itself and run the length, into the gutter, off the edge, whatever the termination.
The solution is simple, the execution may or may not be.
The sheeting needs to be lifted and the moisture membrane needs to be laid and the roof sheeting relocated.
This is usually done in sections.
Alternatively, the sheeting is lifted off and the underside is foam sprayed so as to isolate the metal surface and remove the incidence of precipitation.
Precipitation of this kind forms on all metal surfaces in what is referred to as ‘frost conditions’ on roof pitches from 12 degrees and lower
Using foam to seal off the expansion and contraction of the air volume as exists is not the answer as the void cannot be hermetically sealed unless designed that way to begin with.
Smart thinking goes with the phenomena and not against it.


#10

Ok thanks for all the replies. There is already ice and water covering the entire roof deck, and then the slip sheet, and then the metal roof on top of that. Are you think the condensation is happening on the top side of the roof plywood and making it’s way into the roof (through the slip sheet and ice and water barrier)? I would hope the ice and water barrier would be better than that, and I don’t see any dripping from the fascia (I’m sure not all the water would be getting through). I was assuming the condensation was coming from inside the roof with the metal roof acting as a heat sink on the outside of the plywood.

I hear you on the spray foam, I will not do that.

If I pop off the ridge cap I can cut through the ice and water along the top of the ridge beam and cut or drill vents into each rafter channel along the very top of the roof on both sides. Do you think this would work even without baffles in the roof? I hate to cut through the ice and water with such a low pitch, but I realize it might be my only choice.

One more question, would having air conditioning in that room potentially temporarily solve the problem because it would be dehumidifying the air? I was thinking of of eventually putting mini-split in that room anyway.


#11

With ice and water installed you have a vapor barrier. Condensation is not likely penetrating the ice and water. The condensation is likely forming in the inside and cannot escape, without baffles and air movement there is nowhere for It to go. I would consider paying the money to bring in an experienced roof consultant before doing anything.


#12

Using an air conditioner to remove the moisture simply draws more moisture into the room.
You need to solve the problem which is moisture precipitation directly on the underside of the metal sheet.
When the air contracts in volume, due to loss of heat the roof void, as little as it may seem, the void draws in cool air which is moisture laden. The moisture precipitates on the bare metal and the only way to isolate the bare metal from this reaction is by the methods already mentioned.
High tensile steel roof sheeting is probably the best type of roofing in the world but you need to use it withing nature’s parameters and a low pitched roof, 1 - 12 degrees is the greatest challenge to the inexperienced.
Moisture will always prefer to travel along a substrate as opposed to becoming air borne