We have a playroom upstairs. The ceiling and 2 walls are adjacent to the un conditioned attic. Should the walls be insulated to the same R-value as the ceiling? the walls have sprayed foam in 2x4 walls plus 1" rigid foam with foil on the attic side. ceiling has cellulose at 8" nominal. House is in the deep south. Maybe a dumb question but in this instance why wouldn't the walls need the same amount as the ceiling?
stack effect. hot air moves up, so more heat loss and gain is thru the ceiling. at the top and at the bottom of these knee walls you need to air seal the joist bays completely to avoid air wind washing the insulation and rendering it useless. Basically isolate the unconditioned attic completely from the conditioned space.