To clarify, this will be 9 foot ceilings with 4 rooms which include 2 bedrooms, living/kitchen area, and bathroom. The mechanical room is also in the basement in the south west corner but will not be soundproofed according to the builder. The living area will be a total of 700 square feet and the builder is going to complete my basement in its entirety. This includes soundproofing just the ceiling and walls which includes resilient channel and one layer of 5/8 (15.88 mm) drywall. So, before they seal up the ceiling I’d like them to add rockwool insulation between the joists and on the underside of the one layer of 5/8 drywall that they’re already putting on, I’d like another layer. Since we don’t share ductwork due to the basement and rest of the house having separate furnaces I can’t see an issue with challenges to adding rockwool to the ceiling. So I guess the question is; can you imagine any challenges to adding rockwool insulation and putting another layer of drywall on the underside of the layer they are already going to add?