The house comes with insulation in the upstairs ceiling and external walls but not the internal walls. We thought it would help a bit with sound proofing in the bedrooms if we put insulation in the internal walls upstairs and the study downstairs. This was an after thought since signing the contract. We put R1.5 insulation in the upstairs internal walls which is the same as the external walls.
We also put sound screen insulation in the study walls.