You can install spray foam on the underside of the roof sheathing to create an unvented conditioned attic.
Ceiling roof insulation foam.
Find ceiling foam board insulation at lowe s today.
Some types of thicker foam board insulation are available but they may need to be special ordered.
Spray foam is a very expensive option however.
Typical recommendations for exterior walls are r 13 to r 23 while r 30 r 38 and r 49 are common for ceilings and attic spaces.
Rigid insulation is one of the best tools to reduce your energy costs.
Image courtesy of d7 spray foam insulation houston tx.
Technically known as spray polyurethane foam or spf spray foam is most commonly applied in the space between attic rafters.
They keep your home at a comfortable temperature without the need to crank your heat.
A very energy efficient enclosure results.
In most cases however insulation will not help prevent moisture problems.
Foil faced iso board can be cost effective insulation for finished attics and cathedral ceilings.
Better materials for attic roof insulation are rigid foam boards and spray foam insulation.
Depending on where you live and the part of your home you re insulating walls crawlspace attic etc you ll need a different r value.
You can even place it under the foundation slab.
Even though your attic is large this makes sense because you don t want to install your ducts or hvac equipment outdoors.
Install it anywhere from the roof to the foundation.
Foam board insulation is easy to use and is a great diy way to add some insulation.
Rigid foam board installation in the case of a cathedral ceiling involves installing three different layers that are each 1 5 inches thick according to the procedure discussed in this article appearing in fine homebuilding.
If you decided to use a rigid foam board to help insulate your cathedral ceiling you would install the board on top of the roof sheathing and underneath the plywood at the top of the roof.
It can act as an air and moisture barrier in addition to providing very high r value.
It comes in standard size 4 8 sheets and smaller sizes in many different thicknesses from 1 4 inch to 2 inches.
Foam board insulation would be a more economical especially if you are supplying the labor see photo.