Latest energy codes getting a bit out of hand IMHO. R49 requirement in ceiling areas of my build creates a scenario where I can go with 7" of spray foam, 4" of spray foam and 5 1/2" of Roxul, or double 5 1/2" Roxul and beg for approval since my permit was pulled in 2016 and I understand the requirement then was for R46. The whole thing bugs me out to begin with...all the horror stories of off-gassing, bad mix, etc, however the Roxul will be a major PITA to install. I have just completed a large Roxul install and it took some time and being exposed to it sucked for the most part. Performance wise, a properly applied foam job is superior to any fiberglass or Roxul installed job from all I have read. Yes, the foam guys are trained sales people, and it's true air or water/humidity penetration past or through fiberglass reduces its R-value on the order of 50%. However, properly installed fiberglass or Roxul batts is good enough for me from an energy efficiency standpoint, and to be honest, the last thing I want is an airtight house....or one of those ventilation systems as if there was Radon in the place. I still plan to do a fair amount of Roxul in the exterior walls, so whatever I decide, I will still be dealing with a combinational scenario. All Roxul installed in exterior walls (2x6) will be covered with CertainTeed MemBrain. Ceiling heights are high...averaging around 18 feet. All of the solutions outlined above will be expensive, but no surprise for me as I knew this was going to be a high expense item going into the project...I'm talking around 2300 sq. feet of ceiling to be insulated.
No insulation is perfect. They all are going to have down sides. I’d lean towards foam if you can afford to. A good company will do it right and quick. As far as I WANT TO KNOW, it will only off gas until fully cured.
And if you live in it for like 150 years you might start to see a return on your energy usage for that extra r3!
My biggest fear is finding a competent person/company to mix and spray this crap. My current boss' house got all f'ed up from a bad mix and perhaps spraying in cold temps. Needless to say, he's pissed. The contractor has been back 8 times in attempts to correct his mess. I told my boss to have his roof shingles and sheathing removed, then remove foam ad start again from the outside in. There's the horror story of a well known homeowner in LP who ended up doing this after his contractor screwed up his foam job. The millwork was already up on this particular gentleman's ceilings, so it made economic sense to take his roofing and sheathing off. In my boss' case, I think working from the inside would create a monumental mess and inconvenience since he has already inhabited the place. He's probably breathing all kinds of off gassing by product....not good. Botom line: I'm kinda paranoid about venturing into having the foam sprayed on my place, however, installing a shitload of material otherwise would be a beeache, as I would go up on a scaffold and do it myself to ensure a legit installation.
I had my place sprayed and would do it again. As you say it's all in finding the right people. I'm lucky in that the contractor I use is a buddy of mine whom I trust with everything, so taking his word that the insulation guy knew what he was doing was easy for me.