I am renovating a 1975 Midcentury Modern house and would like to keep the natural wood vaulted ceilings throughout the house. The house is in rough shape, but the ceilings still look good. The house also needs a new roof, so my plan is to remove the (roll) asphalt and take up the sheathing to allow me to replace the insulation from above. I’m guessing there is roll fiberglass in the cavity but haven’t yet opened it up.
My question is what is the best way to insluate? Can I use some sort of rigid insulation or maybe foam? I need something that can be done fairly quickly because the entire roof is going to have to be off the house to get it done.
Any recommendations for material or technique would be appreciated.
Replies
https://www.greenbuildingadvisor.com/article/cut-and-cobble-insulation
I chronicled doing this on a MCM shed roof with a 4/12 pitch (see about 3/4 of the way down in the comments). All told it went smoothly, but you need at least three guys to help (2 to haul stuff back and forth, two to help set materials. Probably took about 20 minutes for every 4x8 area, and we were working pretty quickly). (and the denailer was absolutely key for removing the existing plywood. Made it so simple).
Excellent article - also read Insulating a Cathedral Ceiling. Follow-up question - if I take off the roof and sheathing and do closed-cell spray foam from above (onto the back of the natural wood cathedral ceilings), do I need to fill the cavity completely? If there is a slight gap between the cured foam and the underside of the new sheathing, is that a problem? Thanks.
That's really a question you might pose at Green Building Advisor (and there are serious experts that will answer your question (sometimes a bit tersely, sometimes very generously--always a fount of accurate information). I ended up not doing closed cell for two reasons--immense cost and timing. I would have had to have removed all the sheathing, had walking boards installed, and a lot of plastic protection built to catch overspray (per insulation installer). And schedule issues might have meant having things exposed for a week. Too much risk in the mid-Atlantic. Doing the polyiso "cut/cobble" got me the R factor and air sealing, but with the failsafe of a vented assembly in my case
Thanks for your reply. Two follow-up questions: First, was the roof you cut and cobbled already vented? It seems that makes a big difference in what solution is recommended. Second, and this may sound like I'm a stranger to a jobsite, but how does a denailer help taking off sheathing? Do you just push the nail into the rafter? I appreciate your assistance.
It was a shed roof, 4:12 pitch and 16' wide room. It was vented at the soffit and the peak, BUT, the builder had put in mid-span blocking and it effectively blocked the venting. So I put in layers of 2" and a 1" polyiso to still leave about 1.25" of space on top for venting, and I notched out the top 1.5" of the blocking. So it is now continuously vented. The fact that it was vented also (you can see in the comments) meant that Martin Holladay suggested I should rest comfortably with the cut/cobble method in my case. The denailer shot the nail about another 3/8-7/16" into the plywood, so then the head was simply barely holding a bit of the bottom lamination. The 4x8 panels simply lifted right up. It meant a lot less back-breaking prying of the sheathing off and we could remove a panel and bag the insulation in about 3 minutes flat. I had 3 guys helping me (my landscapers!) and two would carry the debris away while the other guy helped my pound the nails flat to the rafter.