Background: One room in our house is consistently 3-4 degrees colder. I’ve gotten quotes from a few insulation companies, who recommended insulating the basement rim joists and adding insulation to the attic. The attic currently has 4-6 inches of blown-in cellulose insulation, which they recommended topping up to 15". (We’re in northern Illinois, where this matches the recommendation of R49.) One of the companies also said something about the tops of the walls not being sealed? We went ahead with the rim joist insulation, and also recaulked the windows, but haven’t noticed a tremendous difference. Increasing the attic insulation was outside our budget for now, but we hope to go ahead with this next year.
Here is my question: if I were to add cellulose insulation myself to cover just the attic above that cold room to 15", would that make any difference to heat retention in that room, or just be a waste of time without doing the whole attic? Likewise, I know the pros would also air seal the whole attic, which I wouldn’t be doing — would adding more insulation not make much difference without also air sealing?
Also, is this a reasonable thing to do myself? I have gone up there before and walked around on the joists to address a different issue and am comfortable doing so. It seems simple enough — open up some bags of cellulose, spread it around with a rake - but I wonder if it’s a much bigger undertaking than I’m assuming, or if there’s potential for me to do more harm than good. (e.g., I know moisture is a huge issue - do I have to worry about like, if sweat drips off my face into the insulation?)