Insulation, Radiant and Vapor Barriers - Attic Ceiling Insulation

We are converting the attic of our 110 year old home to living space (a studio and bath). In the process, we scabbed on 2x10's to the existing 2x6 roof rafters to get enough depth for insulation. We also added soffit vents and a ridge vent.

Now we are looking into insulation options. We can either go with R25 in the "angled" walls, or R30C (compressed). Just wondering if the additional R-value will be worth the additional expense (special order item). The flat ceiling will be R38, and most of the walls are 2x4, so they will be R15.

We have a couple of small dormers that are 2x4 and 2x6 rafters, so they will be r15 and r19 as appropriate. We didn't want to add 2x10's to the dormers because it would make the ceilings too low.

Thanks!

We are converting the attic of our 110 year old home to living space (a studio and bath). In the process, we scabbed on 2x10's to the existing 2x6 roof rafters to get enough depth for insulation. We also added soffit vents and a ridge vent.

Now we are looking into insulation options. We can either go with R25 in the "angled" walls, or R30C (compressed). Just wondering if the additional R-value will be worth the additional expense (special order item). The flat ceiling will be R38, and most of the walls are 2x4, so they will be R15.

We have a couple of small dormers that are 2x4 and 2x6 rafters, so they will be r15 and r19 as appropriate. We didn't want to add 2x10's to the dormers because it would make the ceilings too low.

Thanks!

Just to add to this, we will have a high efficiency furnace in the attic that will heat the attic space and also the floor (2nd) below it. The 1st floor area (and a small portion of 2nd floor) are heated by another high efficiency furnace in the basement.

We can either go with R25 in the "angled" walls, or R30C (compressed). Just wondering if the additional R-value will be worth the additional expense (special order item).
In no way do you want to compress that insulation there.
Also you have to have the foam vent boards up next the the roof ply so that the vent air can get up over the insulation to the top vents or ridge vent.

ED ;)

We can either go with R25 in the "angled" walls, or R30C (compressed). Just wondering if the additional R-value will be worth the additional expense (special order item).
In no way do you want to compress that insulation there.
Also you have to have the foam vent boards up next the the roof ply so that the vent air can get up over the insulation to the top vents or ridge vent.

ED ;)

From what I understand, R30C is a special, high-density insulation product. It will not be "compressed" when I put it into the space. It is designed to fit into a 10" depth (2x10) cavity.

We will have the foam vent boards next to the roof decking.

My big question is how much of a difference will R30 make vs. R25 in our situation (with the lower insulation values in the rest of the space).