Insulation Question

[Old Moparz]

Sorry, I know it isn't actually a "garage" question, but I've been searching all over the internet for an answer & haven't gotten a clear one yet. I've always seen some good info here so I thought I'd post my question.

What I am hoping to find out is whether I can add some kind of insulation layer to the underside of an existing cathedral ceiling without removing the existing drywall & fiberglass insulation?

I'm concerned about the vapor barrier creating a moisture issue & was wondering if there is some kind of product I can install to the surface of the existing drywall on the cathedral ceiling or on the lightweight T&G cedar planking I will finish it with?

The existing R19 fiberglass insulation has a vapor barrier & is almost as thick as the depth of the 2x8 rafters, so there is little or no air space for ventilation. I plan to correct the sag on the exterior by adding 2x furring strips contoured to the sag once I tear off the shingles. A layer of plywood sheathing over the furring strips will add to the air space I need above the insulation.

For the interior, I am going to do something similar by adding 2x rafters below the existing 2x8 rafters & a lightweight T&G cedar planking for a "false ceiling" below the existing drywall. When I do this false ceiling, I am considering the installation of addition insulation. I was also hoping to avoid the removal of the existing drywall & R19 insulation because of the HUGE AREA it involves as well as the height that needs scaffolding.

There's a new beam (girder) I installed with diagonal bracing that acts similar to a truss. It'll remain exposed & give the appearance of a post & beam structure. The false ceiling will be supported by all the new frame work. Here's some photos of what I am doing inside....

 

[ddawg16]

If I understand you correctly, you are adding a second ceiling under the first one?

Personally, I think I would pull the drywall out...and then attach the new rafters to the existing rafters.....

Man...tough one.....at least your thinking ahead and know you need that vapor barrier.....you have to keep that moisture away from the insulation....that is why I would want to pull the ceiling drywall....I would be afraid any moisture that go past the first vapor barrier would condense on it and flow down to the bottom.

 

[Old Moparz]

I'd prefer to remove the sheet rock & the existing insulation, but the ceiling is massive & extends to the ridge that is literally over 3 stories high. You can't tell from the photos I posted, they only show a small area. The idea was to install the new false ceiling simply to hide the sag that will always remain on the new beam, but get a much better layer of insulation at the same time.

I don't have the budget, the time, or the help to hump sheet rock up 2 flights of stairs & then a ladder to a scaffold.....lol

Anyone know if there are breathable type sheets of insulation?


Here's a cross section to give an idea of the height & size of the ceiling area.