Wednesday, October 22, 2014

Attic Insulation

The central section of our attic was originally insulated with blown-in insulation. The areas above the nursery and guest bedroom, and along the sides of the house are insulated with 12-inch-thick batts. The loose insulation in the attic wasn't particularly thick to begin with - I don't think anything has been done up there between when the house was built and when I started mucking about up there. And me mucking about up there had the unintended side effect of flattening a lot of the loose insulation.

I want to blow in new insulation. After looking at my calendars, it seems like my best opportunity to blow insulation into the attic is November 1st, a week from this coming Saturday.

The home improvement group on Reddit has been pretty unanimous that cellulose based insulation is the best way to go with blown-in insulation. But when I stopped by Home Depot after work today, the workers there (well, the whole two of them I talked to) were adamant that fiberglass is the best method.

All the insulation in the attic is already fiberglass, and part of me is thinking I should mix like with like, and go with fiberglass. But I really don't know. Maybe it doesn't even matter all that much, except to the competing companies that sell fiberglass and cellulose insulation.

I did find out that if I buy 10 bales of insulation, the rental for the blowing machine is free. 10 bales would cost about $300, plus tax, minus a 5% discount for using a Home Depot credit card and letting Home Depot track all my purchases - so 10 bales will cost about $300.

I estimate I have about 600 square feet of attic I want to insulate. As long as I'm going through the hassle of borrowing a blowing machine and getting someone to help me, I might as well go whole hog on this thing: adding R49 insulation to the existing insulation in the attic ought to get me to about R60, and apparently going above R60 is rather pointless in residential settings. (Unless you're Passivhaus - then you can never have too much insulation). So, adding R49 to 600 square feet is about 15 bales of insulation, or $450, plus protective gear (tyvek suit, fresh respirator pads, goggles, gloves). Yikes. That's adding up.

...Brianna? What's my budget for this project, honey?

The worst part is, all of this is ignoring the vaulted area of the great room. I have no idea how much insulation is in that area, I only have a vague idea of how I would even access the attic space above that part of the house, and even less of an idea how I could evenly blow insulation in to the scissor trusses. Right now, I think that will have to be a project for next year, assuming I think it's a good idea at that point.


  1. I would think cellulose/finerglass would be the same (your just trying to trap air). Cellulose might be better since it is recycled product. We have scissor trusses too. you might want to try and put sheets of fiberglass on top of whatever is there....just a thought.

    1. I did think about buying rolled batts of insulation. Two problems made me think blown-in was a better option: 1) The entry access to our attic is /small/. I barely fit through it, and a lot of the rolled batts are wider than I am. 2) There are a lot of joists in the way, and maneuvering around those joists to unroll batts would dramatically increase my odds of putting my foot through the ceiling.