Have a 1930's 2-story house. I recently upgraded the wiring in the 2nd story to get rid of all the knob/tube left in the house, and I figured while I'm up there I should add some attic insulation (this was one of the main upgrades recommended during my home inspection prior to purchasing). Attic is about 600sqft. Ceiling is lath/plaster, there is currently two ~3" layers of fiberglass batt insulation, and then about 10" of blow-in cellulose insulation, estimated r-value was about r-20 by the inspector, I'd like to get that up to r-60ish. Last winter I did have some ice damming on the roof but nothing major, and no moisture issues that were observed (attic or outer walls in the 2nd floor).
I just had a few questions as I'm thinking I need to add some soffit venting:
I believe I don't have any soffit vents, at least it doesn't seem like it. There are six vents near the top of the ceiling, no ridge venting, and two old and small baffle vents on the gable walls. Attached is a picture of my soffit, and the rooms are built along the roof for the first 4 feet. If I want to add soffit vents, is it as simple as cutting holes and screwing on the vent covers from the outside? If I'm doing this, how many vents should I install?
Once I install the soffit venting, I'm a bit confused as to how to install baffles to ensure airflow gets to the attic. The rooms are built against the roof for the first 4 feet as I said above, see picture:
And the baffles I found at home depot are only 4' long. It seems like there is insulation stuffed all the way down the rafters to the soffit, so I have to dig that out I assume, add baffles (can you get longer ones?) then reinsulate?
Again, confused about the on the other side of the house. The bathroom is built into a gable (I think that's the right terminology?), so where do I add soffit vents on this side? (sorry, would add another picture but I'm not allowed!)
Is there an alternative to messing around with all these soffit vents? Maybe just a fan that pulls air in through the baffle vents already installed onto the gable walls?
I was planning on patching the holes I put in the lath/plaster ceiling while doing the electrical work and then spray foaming around the junction boxes to seal, is this fine, or is that a fire hazard?
Local home depot only seems to have blow in fiberglass insulation and it's on sale anyways. Is there any issue with mixing cellulose/fiberglass insulation?