GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Cathedral ceiling demo and re-insulation

pgh_sean | Posted in GBA Pro Help on

I’m hoping to get confirmation that my plan to re-insulate my cathedral ceiling will perform well.  I’ve reviewed How to Insulate a Cathedral Ceiling half a dozen times and read many threads on the topic.

I’m in the process of buying a home built in 1981 in clime zone 5A near Pittsburgh, PA.  It has a gable roof at a 7/12 pitch.  It has 30 or 40 year shingles that are 15 years old.  It needs a lot of work so everything is on the table at this point.  The foyer and family room both have cathedral ceilings (about 40% of the house).  While browsing GBA for ideas to improve insulation and overall performance, I started to learn about common problems with cathedral ceilings.

I have the architectural drawings of the house.  According to them, the roof assembly to finished ceiling is as follows.

Asphalt shingles, 1/2 inch Cellotex or Gyplap sheathing, Rafters are 2 x 8, R19 Insulation, 1/2 inch Sheetrock, Pine tongue and groove

First question, what should I think about this “1/2 inch cellotex or gyplap sheathing”?  Do I need to get under the shingles to see what’s under there?  I guess the real question is… Does the answer impact my cathedral ceiling insulation plan?  If it doesn’t, I don’t think I care.

After a lot of research on GBA this weekend, I’ve come up with my plan.  Since it’s currently R19 (not even half of the recommended R49 for my zone), I’m going to demo the current ceiling and attempt to save the Pine tongue and groove to be reinstalled.

Extend rafters in cathedral ceiling with another 2×8
Site built baffles using 1 inch Polyisocyanurate with a 2 inch vent gap (3 inches, R6)
Insulate the rest of the cavity with cellulose assuming R4 per inch (13 inches, R52)
Dry Wall with air sealing measure (caulk + tape)
Reinstall Pine tongue and groove

There are no issues currently with the ceiling.  That being said, I plan to be in the home for at least 20 years and think this is a worth while project (utility savings, environmentally friendly).

I’m open to any and all recommendations.  I hope I included all the necessary details.


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    BILL WICHERS | | #1

    Closed cell spray foam applied directly to the underside of the roof sheathing would save you a lot of work. That’s what I did in my own house.

    If you do want, or need, to keep it as a vented roof assembly, you can save some money using 1/2” polyiso. The baffles don’t really do anything “structural”, so they don’t need to be very strong.


    1. pgh_sean | | #5

      Good call on the half inch foam.

      The spray foam makes me nervous because you hear horror stories about when it goes wrong. It is an attractive option though. I might do some research and see if there's a good contractor in my area.

      1. Expert Member
        BILL WICHERS | | #9

        There was just recently a thread about spray foam problems. I had posted there that I think people get an overly bad idea of the frequency of bad installations because you hear about the bad ones, but not the good ones. I’ve used ccSPF and zero problems. Many, many other installations have gone fine too, for many people. Just make sure you have a good contractor and you should be ok. What you don’t want is to be some newbies very first job with brand new gear that’s never been used before. Get someone with expierience and good references and you should be fine.


  2. BrianPontolilo | | #2

    As far as the sheathing is concerned, if our roof is only 15 years old, hopefully it was installed with proper details like peel-and-stick at the eaves and an acceptable roofing underlayment. And when you do the demo, you will be able to inspect the sheathing from below and look for signs of problems. So, I don't think there is any reason to peel up roofing from above. An airtight assembly is going to be key for efficiency and to prevent ice dams. And make sure you have enough venting at the soffit and ridge of course.

    1. pgh_sean | | #6

      Thanks Brian, good points

  3. walta100 | | #3

    This calculation of savings of $25 a year based on guesses. In term of fuel dollars saved this insulation upgrade may never pay for its self, if you value your time with today's fuel costs.

    I am not trying to talk you out of doing this upgrade, I just want you have realist financial expiations for this investment. If you want to go ahead for comfort reasons or to fight global warming, I say go for it but do so with your eyes open.


    1. pgh_sean | | #7

      Do you think this would take into account the additional efficiency from air sealing?

      Either way, appreciate it! Regardless of the answer to that question, looks like utility savings is not one of the main reasons to do the upgrade.

  4. walta100 | | #4

    Please have a roofer inspect the roof while you can get the current owner to pay for a new roof. Very few 15 year old roofs will pass a close inspection. 30-40 year shingles are a marketing game as the warrants are prorated with no coverage for labor.


    1. pgh_sean | | #8

      Thanks again Walter. Good advice

  5. walta100 | | #10

    No adjustment was made for air sealing in this calculation.

    I believe that a good air barrier is more important than good insulation. In 1981 some builder did a fair job at air sealing and other made no effort. If the drywall was installed under the T/G ceiling that would make me think this may be a better than average house. Just because it was called for in the plan is no guarantee it was installed, I would want to remove a light fixture and have a look or pull out a nail and look for white on the nail.


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |