Helpful? 1

How to fix an attempted insulation retrofit on a '70s cathedral ceiling?

I discovered this website 6 months too late!

After losing heat through a 70's era cathedral ceiling built on 2 x 8 rafters for more years than we liked to count, we decided to replace the roof, sheathing, and insulation in one operation. The area of the hip roof was bid at 2,230 sq. ft., the cathedral ceiling comprising 2,040 sq. ft., leaving a small attic space above bathroom and hallway areas under the peak.

The building contractor proposed a couple of options to gain R-value, but the real challenge was in providing an airtight ceiling – cedar T&G had been applied directly to the bottoms of the rafters when the house was constructed. The boards were butted to the wallboard on the perimeter of the interior walls and trimmed with molding, but no vapor barrier or other attempt at making a contiguous, sealed, ceiling was evident.

We chose to employ two layers of 3" hard foam (foil faced) placed in the bays, giving us an R-38 ceiling. Not as high a value as I would have liked, but better than the R-19 (maybe) we had previously, plus, we couldn't really afford to completely rebuild the entire ceiling and roof structure/facia/gutters to get more. A great amount of 'pink' foam was used to seal the T&G at the perimeter of the wall and ceiling joint, plus each foam block was sealed against the sides of each rafter bay and to each other. The contractor assured us that we would achieve an 'air-tight ceiling'.

The roofing was nicely done on a 4:12 pitch, incorporating continuous ridge venting along the long hip ridges and a short ridge vent on the top ridge over the small attic space. There is also continuous venting around the eaves.There were also three skylights in the cathedral sections. These clearly blocked the airflow in their respective rafter bays, but cross bay vents were planned. The space between the insulation and the underside of the roof sheathing was minimal (and I suspect not consistent).

The house has been more comfortable this winter, but after a recent week of sub freezing weather (but no snow – unusual for Seattle), we had a sudden rise in outside temperature – hi 40's during the day – resulting in multiple drips in the the living spaces, no doubt the result of the melting of frozen condensation on the underside of the sheathing. The contractor is being pretty slow at responding to my request to mitigate the problem and I am at a loss to envision an expedient way to solve this problem.

My question is this: Is there now any way to positively create an air-seal for my existing T&G ceiling? Do I need to remove the existing T&G or can I build it up with a new membrane and new paneling. If that were done, can we ignore the inconsistent air gap?

Asked by Gregory Erickson
Posted Mon, 12/16/2013 - 20:56
Edited Tue, 12/17/2013 - 06:16


3 Answers

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Helpful? 1

I'm sorry to hear about your problems.

Your contractor chose the "cut-and-cobble" method of insulation, which is not recommended for cathedral ceilings due to the risk or air leaks. Unfortunately, you are now experiencing problems due to air leakage.

For more information on the cut-and-cobble method, see Cut-and-Cobble Insulation.

Your contractor made two other errors, unfortunately: he tried to created a vented roof assembly on a roof with a configuration that is not conducive to that choice (because your roof has hips and three skylights); and he failed to install an air barrier on the interior. Both of these issues are serious.

For more information on the proper methods for insulating a cathedral ceiling, see How to Build an Insulated Cathedral Ceiling.

Now you are stuck with a leaky ceiling with very limited R-value (because the air leaks are bypassing the cut-and-cobble foam).

Here's the bad news: to fix this ceiling, you'll need to install at least two layers of rigid foam on the interior side of your tongue-and-groove ceiling. These layers of foam should be installed with staggered seams, and should be installed with careful attention to air sealing. You'll then need to install strapping and a new finish ceiling.

Personally, I recommend that you install a drywall ceiling. But if you like tongue-and-groove boards, you can install a new T&G ceiling. But before you do, make sure that you have a bulletproof air barrier (verified by the use of a blower door).

Since your current ceiling assembly has failed, an argument can be made that your contractor is at fault. It's up to you to decide whether to proceed by negotiating or by taking your contractor to small claims court. I would start by negotiating, if I were you.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 12/17/2013 - 07:09
Edited Thu, 12/19/2013 - 07:58.

Helpful? 0

Thanks for your excellent assessment and recommendation. Application of a contiguous foam thermal break either inside the roof, as you describe, or on top of the sheathing as described in the How to insulate a cathedral ceiling article never came up in my discussions with the contractor. That is the next step, and undertaking an install from inside the house is the obvious choice as the new roof and solar PV panels were installed after we thought the roof had passed inspection (and a few rains).

I do have one question that I can't fully understand in this debacle. Why didn't we experience the condensation with the previous fiberglass batts? The ceiling should have been even more of a leak factor before the installation of the ridged foam insulation – we'll see how much more after a second blower door and IR camera test next week. Thanks again for your comments.

Answered by Gregory Erickson
Posted Wed, 12/18/2013 - 19:08

Helpful? 0

Q. "Why didn't we experience the condensation with the previous fiberglass batts?"

A. Clearly, one of the changes made by your contractor made the situation worse. Without a site visit, it's hard to guess what factor cause the degradation in the roof's performance, but I'll hazard a guess.

I'm guessing that your contractor's decision to provide "continuous ridge venting along the long hip ridges and a short ridge vent on the top ridge over the small attic space" tipped the roof assembly into failure mode. As I have pointed out in the past, adding ridge vents often causes problems -- because the air that escapes from the ridge vents pulls warm, moist indoor air through ceiling leaks into the roof assembly, where the moisture can condense.

Roof venting is a double-edged sword: it can sometimes help, but it can also cause lots of problems. For more information about this issue, see All About Attic Venting.

Answered by Martin Holladay, GBA Advisor
Posted Thu, 12/19/2013 - 08:04

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