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:

  1. 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? soffit

  2. 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:attic drawing

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?

  1. 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!)

  2. 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?

  3. 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?

  4. 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?


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    You may want to divide this up into two additional questions, especially with respect to the items that veer off the central topic here. – Michael Karas Oct 25 '15 at 17:42
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    The 4 foot baffles can be overlapped to make as long as you require. Shop somewhere else - blow-in fiberglass is terrible in cold as compared to cellulose (too much air movement.) – Ecnerwal Oct 25 '15 at 18:40
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    Your soffits are lower than your living space. The purpose of the soffit vents is to allow cold outside air to easily enter the attic at the lowest point to facilitate warm moist air (in cold weather), which builds up because of the warm, moist living area below the attic, to easily escape through the higher gable end vents or roof vents. But in your case, the roof area immediately higher than your soffits is part of your living area envelope and you're going to have it all sealed and insulated, right? – Craig Oct 25 '15 at 20:10

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