Insulating garage ceiling

[jmgreen7]

I'm only posting this because specific questions i have regarding insulation are not covered in other threads.
Background:
my garage ceiling joists run the width of the house and run directly into the basement. The people who installed the insulation initially did not block off between the garage and the basement. There is insulation, but it is obvious that there is air movement between the 2 rooms. The garage is already drywalled on the ceiling, and bare cinder block on the walls. insulation in the ceiling is faced and placed facing the warm side living area above the garage.

What i plan to do:
1. I would like to block airflow into the basement by pluggin up between the floor joists.
2. Pull drywall and replace/improve the existing insulation.
3. Frame in cinder block wall and drywall.


What i want to know...
1. Is rigid foam blocking and caulk appropriate as an air barrier between the garage and basement.
2. if i choose to stick with fiberglass batts, can i layer it 2 thck to fill the entire void, or does the open air between the batt and ceiling drywall serve a purpose. I currently have an 8 foot ceiling with garage door openers. I live in va south of dc, so my cilmate isn't too extreme in any direction.
3. should i consider 2 inch rigid foam between the floor joist and drywall?
4. better option//implementation than the fiberglass batts?
5. opinions of roxul vs fiberglass batts?

I can post pictures to better explain if needs be.

 

[rburke65]

I'm thinking some photos would greatly help.

 

[DC73]

The air gap between the insulation and ceiling drywall has an R value but insulation has a higher R value and there shouldn't be a problem with completely filling the void with insulation.

Roxul is mineral wool based, will be better for fire protection and will be better for blocking sound. Other than that, R value is R value and the fiberglass will work.

You might consider spray foam for both the ceiling and the wall (after framing). Closed cell spray foam would completely block air movement, vapors etc into the living space above and into the adjacent basement. You could cut some costs by doing a "flash and batt", which means a minimal layer of spray foam to do the sealing and then come back with fiberglass or Roxul for the remainder of the R value you want. There's a way to calculate how much spray foam is needed to avoid condensation issues within the remaining insulation but it's based on your climate and I don't remember the particulars. A good spray foam company should understand your climate and what is needed.

BuildingScience.com has some good information if you have time to wade through it all.

DC

 

[jmgreen7]

Files are attached. The third picture is looking toward the basement, you can see the darkened insulation. that is all dirt that has been absorbed due to air movement between the garage and the basement (located on the other side of the cinderblock wall).

the rest are just different views of the current insulation installation.

 

[jd_77]

I would block each hole with a piece of wood and then spray foam on the basement side. That should seal it up pretty good.