I have this tiny little CMU building, with wood sheathing as the roof deck (vaulted), exposed from below. The architect seems to remember some type of spray on insulation that he thinks can be sprayed onto the underside of the deck and it will just stay attached to the plywood and insulate the little building. Appearance is not a concern. Any suggestions for a gravity-defying spray insulation taht will adhere to the plywood deck?
Try the spray applied exposed insulation section:
http://www.4specs.com/s/07/07-2300.html
Get a look at the substantial discussion on “hot” roof insulation at www.buildingscience.com. Joe Lstiburek has done a lot of study on the overuse of ventilated attics. He’s monitored a bunch of buildings in several climates using spray-applied high density urethane foam installed directly to the underside of roof sheathing as you propose. The stuff is as tough as Gorilla Glue when it sets and will not come down; I’ve used it on my own projects. Needs plastic thermal separation protection in occupied buildings. Well known manufacturers include BASF and Demilec.
if you use a foam spray, it will need a 15 minute barrier to heat on the interior. Instead, check out International Cellulose Corporation at www.spray-on.com They have thermal and acoustical spray systems that can be the finish also.
In this condition, I have used laminated panels. They have nailable base for asphalt shingles, laminated to foam insulation. You can get them with ventilation channels under the nail base so the shingle manufacturer will give a warranty. It may be available with the sheathing as well, requiring only a single step to install–I haven’t checked that.
We looked at cellulose at the underside of a roof deck, and the manufacturers told us they would not warranty the installation without something below to hold the cellulose in place.
Depends on the cellulose supplier and their products. K-12, Monoglass and Thermacoustics (see link above) are designed to be exposed and have a water-activated adhesive in the mix. Most wall cavity cellulose products do not and would not work.
In addtition to the SIP noted by John B, consider a 2-component closed-cell polyurethane foam by BASF; “Spraytite 178 Series” and a spray-applied thin film thermal barrier. Another is Demilec “Polarform PF7300”; www.heatlok-soya.com
For a thermal barrier checkout BioBased Systems “No-Burn Plus” fire retardant www.biobased.net. There are others from Grace and I believe, Isolatek.