Proper R-Value/insulation type for between living space and attic area above garage?

Question

My house has an unfinished attic area about the garage. This is on the same level as the upper floor of the house. The wall towards the living space is adjacent to a bedroom, the upstairs hall, and the stairs going up. The interior gets very cold in the winter in this area so I'm hoping to improve the insulation. There is some existing insulation but it looks like someone took some scraps and jammed it in between the studs rather than doing a quality job.

Everything I've seen with regard to R-Value for insulation refers to either walls facing the outdoors or attic floors. What is the proper R-Value for this scenario?

Any special considerations regarding type of insulation or features for this scenario?

I'm in the US in NJ in zone 5.

Answer 1

For purposes of insulation, a wall common to conditioned and unconditioned spaces should be treated as any exterior wall. Modern standards would be R-19 fiberglass batts (or R-13 for older 2x4 walls), or something modestly above that with spray foam.

Assuming a proper firewall (5/8" type X gypsum panels, joined over framing members), no special material is needed for the insulation.