Insulated attic ceiling

I am homeowner and not too familiar with roofing. I plan on doing a tear off and replacing with shingles. I am worried about ventilation. My soffits are not vented. My eaves are solid so even if I put in soffit vents no ventilation. My attic ceiling is insulated with fiberglass batts with wood paneling over the top of the fiberglass, so even if I vent soffit/eaves, the airflow would be blocked to get to the ridge vent. Does fiberglass batting allow enough air to flow through it for ventilation? Or in my case, is it better than nothing such that I should vent the soffit/eave? My attic floor is insulated with plywood on top and I use it for storage, but it is otherwise an unheated space. This is Montana so we can have 90 plus degrees in summer and 20 below in winter. The attic has a window on each gable end and I keep those windows open from spring through fall for ventilation. Existing roof has ridge vent and would replace likewise. My questions: 1. Do existing windows and roof vent provide adequate ventilation? 2. Would installing soffit/eave vents be worthwhile even if fiberglass insulation remains? 3. Is tearing out the fiberglass insulation the only option (the attic floor insulation is asbestos vermiculite, so I hate to spend a bunch of time up there stirring things up)? 4. Could a synthetic nonpermeable underlayment exacerbate moisture problems, if I have any to begin with? 5. The roof has been on for decades, so if the decking looks fine, could I just as easily assume I don’t have a ventilation problem to begin with?

Sometimes it is necessary to remove the roof sheeting to install rafter/proper vents, this is easy but time consuming.
Combine this with a continuous soffit vents and ridge vents, the results are usually very good.

If you don’t experience any ice damming this may not be needed at all.

Hi atwood

No…fiberglass insulation does not allow for proper ventilation. If you have plywood on top of the insulation as your attic floor you do not have enough insulation to provide the correct R-factor. Call your local building inspection department and ask what the code is for your area.
Having open windows on the gable ends and ridge vent makes no since. They short circuit the ridge vents. If you install soffit vents you must also install baffles between the rafters to allow for air flow to the ridge vents.

Stormer - The house was built in 1930s and we bought it a year ago. Attic was inspected for insulation and does not have proper R-value. We blew in cellulose behind the knee walls, but for the rest of attic we left as is because we did not want to give up the storage space.

Axiom and Stormer - So I could remove sheathing, attach baffles to back side of sheathing, put sheathing back on, install soffit and eave vents, and reinstall the ridge vents and that may do the trick?

I have not had any ice damming problems this past winter, so maybe the house breathes well enough on its own. It is built in 1930s so I assume not very tight.

I

Just make sure you have a space for continuous airflow from the lower eaves up to ridge, even if it’s only an inch between the sheathing and baffle vent. Ice dams aren’t the only problem. Asphalt shingles will break down prematurely from heat if they are installed over a poorly vented surface. I’ve seen many asphalt shingle roofs less than 10 years old with bad heat damage from poor ventilation.