Down here we use open cell above grade and closed cell below Building Science articles do mention both cc and oc being used in attics, but they explicitly recommend cc. See "Unvented Roofs for All Climates" and "Understanding Attic Ventilation" (See Link below.) As I mentioned above, cc is excellent in attics as it acts as a secondary liquid water barrier. At the same time, it is permeable, allowing vapour to move both ways depending on the season. As for "hiding" leaks, I have seen commentary from foam appliers who handle all kinds of foam say that in case of leaks cc focuses the water, so it's easier to spot the source. Because oc foam is more permeable and holds water, the R value is degraded, which means the sheathing is more easily reaching dewpoint, which is not desirable. The same logic applies below grade. The one time I used oc foam, it was applied in cold weather and shrunk back considerably around the rim joists; this is recognized in the literature but brushed off as a minor quibble. When I've used cc foam in basements, rim joists, garage ceilings and attics (but not under the decking) I had none of those problems. Clint Eastwood's Dirty Harry had a famous comment about opinions--that I won't use here. That's why I try to reference mine to Building Science, whose principals are among the leading building scientists around; and who are also the source of much info at the US Energy Department --Energy Efficiency and Renewable Energy--Building Technologies Department. Here is a link that might be useful: Vented and Unvented Roof Recommendations

When you are looking at new construction. Blown in fiberglass is the better choice over blown in cellulose. For one R-factor is clear when you look at each individual manufacture's spec. Blown in fiberglass in 2x6 walls get an R-23 vs. cellulose gets an R-20.6. You can get a better R-factor in a ideal setting no wires, in cavity with high density fiberglass blanket/batts R-21. Blown in fiberglass is maybe a fraction of extra cost but no more if you go with dense pack cellulose with a netting. Which by the way if you do insist on going with cellulose make sure they install dry pack with netting. I don't know how many times I have seen mold law suits that have involved wet-spray cellulose. Wet spray you have to wait in ideal setting 72 hours (that's by the way 70 + degrees and almost zero humidity) before you can cover. How many times will the ideal setting happen during that stage of building? Which is not even the worst part, if you are planing to have cabinets installed on the exterior wall, guarantee if you went with wet spray cellulose you will have a mold issue there. I have been around insulation for over 14 years and for some reason a lot of people have never even heard of blown in fiberglass almost every one associates fiberglass as being the preformed batt/blankets. And if you look at most fiberglass versus cellulose side by side comparisons they always show the blanket/batt form of fiberglass why? Because that is the only thing cellulose is better than is the blanket/batt form because of the perfect fit scenario. In fact in studies from fiberglass companies show blown in fiberglass is up to 70 percent better than standard blanket/batt form fiberglass in air infiltration. They even have a sample where one side of cavity is blanket/batt then other side is blown in tight and you have a hair dryer attached blowing through both materials at the same time. The blanket/batt side reaches temps of 130 degrees while the blown in tight fiberglass only gets to 85 degrees. But blown in fiberglass you get both worlds perfect fit and highest R-factor. As to the case which products works best in ceilings. Again there is no specific studies that I have found in my research that is non-biased that says Cellulose is better than Fiberglass. Why is that? Because cellulose is not better than blown in fiberglass. If both products are installed to manufactures spec in inches then they will perform the same, until cellulose settles 20 percent as it says on the actual bag of material. In all the thousands of attics I have looked in almost every one that was installed with cellulose had settled below original suggested R-value at least 20 percent. The only time fiberglass need to be fixed is because of contractors or tradesmen have been up in attic and they never replace the insulation or they stomp all over it until there is nothing left but the depth of the bottom cord of truss. Also the rumor of cellulose being better in extreme cold temperatures I personally have found to be amusing. My brother lives in Alaska 40 degrees below zero and I asked what kind of insulation does he have in his house? Guess what it was fiberglass insulation. Bottom line fiberglass is better in exterior walls new construction and it performs the same at first in ceiling until cellulose settles then in the long run fiberglass is preferred between the two most common blown in insulation. Now if you have at least double the normal budget for your house then I would strongly recommend at least 1" thick sprayed closed cell urethane then covering the 1" spray with either blanket fiberglass or blown in fiberglass. Blown in still being the better option over blanket because of the perfect fit concept. This application completely shuts off any air movement in the wall cavity thus helping the fiberglass do its job to a better ability. One more word to the wise make sure you go with closed cell when you go with foam insulation. Open cell is no good it will absorb water like a sponge, and the R-factor is not there you can get better R-value per inch in blown in fiberglass in exterior walls. Well this has been my experience the past 14 plus years in the insulation industry. Take it for what it's worth. I hope this helps people. I feel I may have done a little to much rambling. Sorry for so much confusion that is out there. I really am only doing this to try to help combat all the confusion.

I've seen that flame spread video before and it is clearly intended to give the impression that cellulose will protect wood studs from fire which is not relevant to fire protection in a home. What protects rooms and structural framing from fire is gypsum wallboard (GWB). When exposed to fire, GWB releases water vapor cooling its surface and preventing the materials inside the wall (studs, insulation, wiring, etc) from getting hot enough to burn or melt. A fire resistance rating is the time it takes for a certain temperature to be reached on the face of the wall farthest from the fire. That temperature will be reached long before fire breaches the GWB. At the end of the test, the wall surface must remain intact when water is sprayed on it from a fire hose. Since insulation is normally installed in exterior walls, it would have little value in fire protection even if it did increase the fire resistance of the wall. In a single-family house, walls and ceilings are not normally required to meet a fire-resistance-rating but a layer of standard 1/2" GWB on each side of interior wood studs (with or without insulation) should give the occupants enough time to escape and the fire service time to arrive. However, the greatest risk to life in a home fire is the rapid spread of smoke and super heated gasses from between rooms through doorways. If you are concerned about fire safety in your home, rather than worrying about insulation, put automatic closers on solid core bedroom doors or install a quick response residential sprinkler system. Since insulation is usually placed in exterior walls it has list IMO the best insulation is "Dense-Pack Cellulose" but it is not offered in all markets. Netting is installed over the studs and cellulose is sprayed through it to a high density. If your GC doesn't know about cellulose in walls he is unlikely to know about dense-pack. But the insulation sub might know about it so he should be present when you are discussing it with the GC.

Our most recent project was half gut rehab/deep energy retrofit and half new construction. The cost for rehabbing the old part of the house was only somewhat higher than the new construction, about $425/sf vs $350/sf. (typical new spec houses in our area sell for $300-$400/sf, not counting land costs. We got much nicer finishes inside at a similar price by DIYing all of the interior trim, floors, painting, kitchen cabinets, etc) Dollar wise it was close to a wash vs a teardown because there would have been added costs in the teardown process, plus a much more complex permitting and zoning variance process. More importantly we saved many dumpsters of good quality old material from going to the dump. It's not as grim as Sophie portrays.