Best insulation for situation

[bmxer883]

So this isn't a garage but hopefully I can get some good suggestions. I have a 1/1/2 story house and had half of the upstairs spray foamed with closed cell to back side of roof. A lot of people have there opinions on it but it's already done and not changing.

So we are looking at finishing the other half of a closet space right now it has some fiberglass insulation but looks pretty nasty. I wanted spray foam but moneys to tight so I'm trying to figure out what's second best. The roof rafters are 2x4 so only 4in of room to insulate and they are like 28in apart kinda random measurements.

I have a decent amount of left over purple 2in foam board from doing a basement floor. So I'm wondering if I should cut and fit it in rafters and just can spray from around it or and some nailers so I can put fiberglass in or is there a better option like rock wool or something?

Picture with spray foam is how some of it was already done other picture is the one I'm looking to replace insulation.

 

[duneslider]

Your cut and cobble with the purple rigid and can foam for seams and gaps is a good method. Is this attic space a conditioned space? If you get is all insulated and air sealed it could be.

Using rockwool won't do anything to help with air sealing, but the cut and cobble will help with air sealing and ultimately help reduce ACH which will make a difference.

 

[bmxer883]

Yes it's technically conditioned now the actual attic use to have roof vents they are now covered and everything is sealed by spray foam from what I have read it may shorten life of shingles but it's okay other than that. My attic stays cool now in summer.

If I use the foam board is 2in enough that would be r 10 but sealed with no air flow

 

[bmxer883]

Here's how it's turning out. While taking down old fiberglass it was moist and all the nails sticking through were dripping water so I'm guessing there wasn't enough insulation causing condensation? It also wasn't sealed very well.
I'm hoping the foam will be enough. It's currently been in the 30s