I read the good article on building a vaulted ceiling — too late
I read the good article on building a vaulted ceiling. However, that is too late for me since I already have vaulted ceilings throughout my house.
In the areas where there is unobstructed venting from the soffit to the ridge vents all is well. But in three places I also have large dormers framed into the vaulted ceiling. Where the rafters intersect the valley rafters it creates a dead space where there cannot be any air circulation although in each case there is a ridge vent. The rafters are TGI 14″ with R30 insulation batts sealed with visqueen. However, the finished ceiling is tongue and groove spruce.
After researching on your website I now know the mistakes made in construction. But, what can I do now to alleviate the condensation problem? I am in zone 5B at 8,000 feet altitude and even though there is much snow in winter it is still very dry. And I keep the humidity low in the house 10-20% but still get condensation and then thawing in spring and dripping down the walls. I am attaching pictures.
Any help will be appreciated.
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Replies
Gene,
As you now realize, your ceiling isn't airtight. Lots of indoor air sneaks through the cracks in your ceiling boards. The polyethylene isn't an air barrier either.
You can either fix the problem from the interior -- by installing a layer of taped gypsum drywall to cover your board ceiling (this will be your air barrier) -- or from the exterior (by opening up the roof, throwing away the fiberglass batts, and installing closed-cell spray foam from above).
Neither solution is cheap, unfortunately.
(If any GBA readers are curious about "the good article on building a vaulted ceiling," I think that Gene Byrd is referring to this one: How to Build an Insulated Cathedral Ceiling.)
We had to take a T&G ceiling down and put it back up again once due to a similar problem. in our case the boards swelled enough that we had some buckling going on.
It actually went very quickly. most of the nails pulled through the boards and stayed in the ceiling framing, we bent them down, installed 6 mil clear poly and put the boards back up it took a three person crew a day and a half. the wood was largely un-harmed.
I wouldn't put clear poly on every ceiling in a house but have never had a problem from putting it behind the ceiling of a single room. You could also use taped T-ply and I've also used taped Tyvek.
I certainly agree with Martin that drywall with a vapor retardant paint is the proper way to prep a cathedral ceiling for wood. And it's very affordable if you do it when the rest of the building is being drywalled.
Michael,
Thanks for sharing your experience. It's possible to create an air barrier with polyethylene, but as Gene's experience shows, poly doesn't always work. Sometimes a layer of poly ends up with lots of holes. There may be rips in the poly that fail to get repaired in time, there may be electrical boxes or recessed can lights, or there may be polyethylene seams that aren't properly sealed. (If you really want to use poly as an air barrier, all seams have to fall on top of a piece of framing lumber, and must be sealed with Tremco acoustical sealant.) And then there are all those fastener penetrations -- the nail holes that occur when you nail up the T&G board ceiling.
It's far safer to establish your air barrier with drywall. Then, if you want the board-ceiling look, you can add boards as the finish ceiling.
Martin and Michael, thank you for your responses. They prompt several questions and comments.
Martin, your solution to take off the roof and spray in closed cell foam raises the question of what happens to the moisture which penetrates the ceiling. I suppose the foam insulation would prevent it from freezing but wouldn't it still be there and potentially run to a place where it would leak. Your solution to seal the ceiling with sheetrock and then ceiling boards would be the most guaranteed, but it certainly would be the most expensive and disruptive. Michael, seems like your problem was moisture collecting on the T&G ceiling itself - rather than in my case, the moisture is penetrating up to the roof sheathing and freezing. So, it seems I need to seal the rafter cavities better with poly (being careful to not make any holes or leave any seams open. But, as I said originally, the areas where there is open ventilation from soffit to ridge, there has been no problem. This leads me to think that if there were some way to get ventilation in the dead space rafter bays that the problem would go away. If that is the case, is there any way to get air into those spaces, such as a small roof vent or opening a space through the rafters to access cross venting? Michael, your day and half project is about what I have thought mine would take. Just dread moving all the furniture, protecting floor, and putting up scaffolding, (my ridge beam is 21' from the floor!}. Thanks again and will appreciate any further comment or clarification. Here is another picture.
Gene,
Q. "Martin, your solution to take off the roof and spray in closed cell foam raises the question of what happens to the moisture which penetrates the ceiling."
A. Your ceiling assembly is not supposed to be a dehumidifier. The point of your ceiling is not to remove moisture from the interior of the home.
During the winter, the indoor air in your home is warm and humid. That's the way it's supposed to be. The outdoor air is cold and dry. You don't want to have any leaks in your building envelope. The idea is to keep these two environments separate -- the warm, humid interior and the cold, dry exterior. So you want to build a house that keeps these environments separate. You certainly don't want to encourage moisture to enter your ceiling assembly.
What happens to the moisture in your house? Ideally, it stays put. Right where it is. The reason that your ceiling is dripping is that some of the moisture escaped through cracks in your ceiling. That's bad.
Q. "If there were some way to get ventilation in the dead space rafter bays then the problem would go away."
A. Ventilation will not solve your problem -- especially if you have a dormer. The problem is air leakage.
If you go to the trouble of removing all of the boards on your ceiling, I strongly urge you to install a rigid air barrier -- not just polyethylene. If I did this job, I would install a layer of foil-faced polyisocyanurate with taped seams under the rafters.
Thank you. I discovered an exchange about a very similar problem starting in Dec. 2011 (“How to stop a Cathedral ceiling from sweating”).
Here is a quote:
"Newly constructed home in upstate New York (Cold Climate) with cathedral ceilings throughout. R38 paper faced batts with Sheetrock and T&G pine cover the entire ceiling. After the long winter months have past the warmer weather causes water to come streaming down the inside of the valleys and down the walls for at least 5-6 hours. A roofing contractor said it was caused by ice damning so I replaced the shingles, s&i guard etc. in both valleys and I had a leak this past Sunday afternoon (no rain or snow). I don't know what to do besides rip down the ceiling and spray foam.
Asked By scott davis | Dec 6 11"
Can someone please bring me up to date as to how Scott solved his problem?
Gene,
If Scott is still a regular visitor to GBA, perhaps he will show up to answer your question.
It should be pointed out that these dripping cathedral ceilings -- many of which are finished with tongue-and-groove pine boards -- are extremely common. Another one just showed up on our Q&A forum today: Leaking ceiling when weather shifts from cold to warm.
Good Morning Gene,
My solution has yet to be fully tested but it proved sucessful during our January thaw. Working from the exterior, I remove the sheeting and fiberglass batts from between all valley rafters. I then worked my way up the roof line spraying foam 4' at a time, I installed and filled the valleys one sheet at a time which allowed the foam adhere to the underside of the plywood. I discovered that my biggest mistake was installing the styofoam vents in the valley, they actually were acting like a big funnel system during the thaw. I believe this problem exist in many more homes than we think, If these vent were not installed the fiberglass batts would have soaked up the moisture and I would not even had known a problem existed until I went to replace the roof in 30 years. Hope this was helpful, believe me I feel your frustration.