Hi all, I recently bought a 150+ year old row house and am having thermal comfort problems on the 2nd and 3rd floors. I was able to diagnose the cause easily (poorly insulated and air sealed ceilings and kneewalls, compounded by an infestation of attic mice who have been carrying off some of the insulation to make nests). My conundrum is how best to solve it. Applying spray foam to the underside of the roof sheathing and bringing the attic inside the thermal envelope would be the simplest fix, but would definitely cost more and I’m not a fan of the environmental impact of spray foam. Alternatively, I thought of another solution (see attached) that involves air sealing, removing old insulation, and re-insulating with blown cellulose, and also using wire mesh to block potential rodent access pathways. My only reservations with this are A. could adding more insulation cause moisture problems if I’m not able to air seal well enough? (my attic is unvented and the only place it would be possible to add venting is the ridge), B. Could I potentially make the rodent problem even worse? (I know there’s no way to block off every single possible path for rodent access) and C. Would the improvement in comfort even be worth it, or would I rather just spend a few thousand $ to avoid crawling around in nasty attic space? 

Thoughts? (For context, I’m in climate zone 5)