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Insulating a non vented vaulted ceiling…..?

user-1085290 | Posted in General Questions on

i am hoping to get some feedback on the issue I have found in my house while redoing our dining room. The electrical issues that can be seen in the photo’s are one of the reasons I pulled the drywall to begin with and are being corrected. My dilemma at the moment is how to properly insulate this area of the house.

The roof/ceiling is 2×4 construction and pretty much “Non Vented” (to the outside of the house anyway). Whoever re drywalled this room at sometime before I owned the house installed FG insulation in some places and none in others. It was poorly done. The drywall is chalky and feels dried out. I am going to pull the rest down and redo it all but my dilemma lies in how to insulate this area the right way.

In this photo it shows the lower side of the room. The wall joins the dining room and our garage… Sooo obviously not vents here.

In this photo, It shows the higher side which shares the wall with out kitchen. There is no blocking and it is open to our attic space.

Here is an overall shot of the ceiling.

Here is the adjacent room that is also vaulted. This has been poorly insulated as well (from the inside and covered with bead board) and is going to get redone. This room has 4×6 beams, T&G for the ceiling.

My plans are to have it insulated from the outside when we redo our roof so that we can leave the beams and T&G exposed.

I am in Southern California FYI. (zone 3-c)

Any input would be much appreciated!

Thanks in advance!

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  1. jklingel | | #1

    There are a bunch of threads here and on that explain how to insulate and air seal roofs. Do a quick search and you'll likely be set.

  2. user-1085290 | | #2

    Thanks, I have been researching all day today and have found some great info both here and on

    Still not sure I have found all the answers or what is the best solution for me, but that could be just been from information overload today.

  3. GBA Editor
    Martin Holladay | | #3

    J Loc,
    Start with this article: How to Build an Insulated Cathedral Ceiling.

  4. user-1085290 | | #4

    Thanks for the link.... Very informative. I think I may need to have a roofer come out and look at insulating the T&G part of the roof and go from there. Becuase the two rooms share the same part of the roof, whatever I do in our dining room to insulate on the inside might not be ok with how the insulate from the outside when I get that done. At least that is what I got from some of what I have read.

    Our house only has gable vents and no soffit vents which has not made my research any easier to find what I need.

  5. user-1085290 | | #5

    So I have had two roof estimates so far, and both contractors suggested foam board with ply on the exterior directly over the T&G. Non ventilated. I have one more estimate coming tomorrow so we will see what process they recommend. So If go solid foam on the exterior, I just need to figure out what to do inside to insulate it properly in the dining room where drywall will be installed.

  6. GBA Editor
    Martin Holladay | | #6

    J Loc,
    Just be sure that the insulation meets minimum code requirements. In Climate Zone 3, you need at least R-30 of roof insulation. That's about 5 inches of polyiso or 6 inches of XPS.

  7. user-1085290 | | #7

    I did ask each of the contractors about the code Req. on insulation thickness and because it is not a new structure, all stated we could put anything I wanted from nothing ( how it is now ) to 6" if I choose.
    I still haven't been able to find a cut and dry answer on how to insulate the dining room properly before re-installing the drywall if we do rigid insulation on the outside.

  8. user-1085290 | | #8

    So I am back on this project. I was busy with work and gathering estimates and info in the last couple of weeks but have a couple questions after re-reading the info posted in the link below.

    Under "Can I build an unvented roof assembly?"

    "Remember: if you choose to install rigid foam on top of your roof sheathing, don't install ventilation channels under the roof sheathing; these two practices are incompatible."

    and then..

    "To summarize, there are three ways to build an unvented roof assembly:

    Install rigid foam insulation above the roof sheathing and air-permeable insulation between the rafters. If you choose this method, it's possible to install vent channels between the top of the rigid foam and the top layer of roof sheathing by installing a series of parallel 2x4s — one above each rafter — extending from soffit to ridge."

    It say's it is "possible" to install venting below the top layer of sheathing.... Do I really need to do this?

    At this point.... From everything I have gathered, We are planning on doing the following:

    Install rigid ( have not decided on which kind or thickness) insulation on the outside when we do our roof, and R-13 batt's in the rafter bays and finished with drywall on the inside. Non vented.

    Am I on the right track?

  9. GBA Editor
    Martin Holladay | | #9

    J oc,
    Q. "It says it is possible to install venting below the top layer of sheathing.... Do I really need to do this?"

    A. No, although the ventilation channels may reduce the chance of ice damming in cold, snowy climates.

    Q. "We are planning to install rigid insulation on the outside when we do our roof, and R-13 batts in the rafter bays and finished with drywall on the inside. Non vented. Am I on the right track?"

    A. You are on the right track, as long as you remember that building code requirements call for a minimum of R-30 foam (5 inches of polyiso or 6 inches of XPS) when building this type of unvented roof in Climate Zone 3.

  10. user-1085290 | | #10

    Thanks for the quick reply!

    Yes, the rigid foam has yet to be determined on what they will require as it is an older structure and not new. The local roofers who I had out for estimates said 2-4", but we will see when the time comes. Either way, what ever is required.... we will do.

  11. user-1085290 | | #11

    one more quick question...... When they redo the roof, they are going to leave the skip sheathing and go over it with ply. Do I need to worry about any side to side ventilation with the skip sheathing remains intact?


  12. GBA Editor
    Martin Holladay | | #12

    J Loc,
    Since you are planning to install insulation above and below the skip sheathing, you'll have to make sure that the perimeter of the skip sheathing is air-sealed. You don't want the exterior air to mix with the air between the old sheathing boards.

    In order to air seal this layer, you may have to use spray foam at the perimeter of your roof.

  13. user-1085290 | | #13

    Thanks, Thats what I was thinking would be necessary.

  14. Expert Member
    Michael Maines | | #14

    J, regardless of what your roofers say, you should listen to Martin's advice to go with at least code-minimum insulation levels on the exterior. Roofers are not known to be building science experts (aside from Martin). The minimum foam thickness is specified to keep the framing above the dewpoint; if you are going to use batts within the framing cavity you WILL get some warm, moist air in the framing cavity too. The thick layer of foam keeps this water from condensing and causing problems.

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