I've been reading, and reading, and reading, and I think I'm more confused than when I started, so I'm posting.
I have a 1905 Queen Anne, it's about 2200 finished square feet. The third floor/attic is partially finished I guess... it has real stairs leading to it, and tongue in groove flooring covering most of the floor (minus a few bits where it's either been removed or just wasn't done in the first place). It's basically a steep hip roof, with extra complications since it's a queen anne (including one corner that's a partial witch's hat turret but intersects the roofline, leaving an interesting internal space in the attic. I don't have exact measurements, but I believe the tallest point in the center is about 20 feet.
A previous owner attempted to insulate it, apparently piece by piece as he was able to pick up insulation cheap or something. The home inspector's comment was something like "this wouldn't be too bad for a DIY job, if he hadn't left enough gaps between bits that it might as well not have any." The turret has none at all, and I can notice the difference from that bedroom to the other ones, though it may be because the rounded glass windows badly need restoration and have gaps large enough to put a finger through (the gaps are caulked over now).
Anyway -- I love the space and I'd like to finish it off. I want to rip out all the badly done insulation and have a professional come in and do it properly. When I researched it a year ago thinking I could afford it then, I decided that the best option was to do the whole roof with 6 inches of icynene and then put up something like stained beadboard to cover it but still keep that sort of aged wood feel. I brought in an insulation company for an estimate, but because I'd had to agree to pay for most of the fireplace restoration myself to get the sellers to agree to close, I didn't have the cash to do it then.
The quote, btw, was about 6k, and included ripping out the old insulation and disposing of it properly, using icynene on the roof and the.. uh.. I think it was rim joists and some bits in the basement or something? And also over a room on the back that was a later (1930s?) addition and appears to be completely uninsulated. They were also going to blow cellulose into all the exterior walls.
It seemed like reasonable suggestions, and echoed what the home inspector had said probably needed to be done when I first looked at the place. I just ended up not having the ready cash to do it.
So, now, I've got the cash, and as I went to do some more research, I come across a boatload of people screeching that open cell foam is the devil and only closed cell is safe; and people screeching the opposite.
I assume that a big part of the determining factors is the location/climate of the home: It's on the indiana/michigan border, so the heating bills are the more expensive part by far. I had a $300 gas bill for December and that's with programmable thermostats dropping the temperature to 55 when no one's home and only taking it up as high as 68, ever. And I don't think the climate is probably hot enough to worry about the shingles being damaged by the heat (but I could be completely mistaken there). We do get very heavy lake effect snow, which may also be a consideration (if the roof springs a leak, we need to know about it very soon, because finding out by having it rot unseen and collapse under a mountain of snow would ruin anyone's day). On the 1/7 weekend timeframe, we had about 36 inches pile up in my yard, most of it in the 24 hours from 7am friday to 7am saturday. But that's much much more than usual... 16-20 inches is far more common.
Another big part is probably the construction of the home... since it's a century old place, it breathes a lot, and even filling in the walls probably won't prevent it from breathing sufficiently.
Not sure if the reason for doing it comes into play, but just in case: Finishing off the attic will allow me to use it as dedicated office space for my consulting business, but with the possibility of converting it into living/entertaining space later on (the first thing I thought when I saw it was "wow, this would make a killer home theatre").
So... anyone familiar with old houses in upper midwest climates who has a definitive answer on whether open cell or closed cell foam is better for this application, and why? And if there's any reason not to use the blow-in cellulose in the walls? (Exterior walls are about 60-70% clapboard, 10% limestone blocks, and 20-30% cedar shakes... we won't be blowing any insulation into the limestone though :) )
Sorry this is so very longwinded. Thanks in advance for anyone who can offer good counsel.