One aspect of the invention provides a including: (a) placing N×N max size buffers at an (n−1)st level of one of the voltage domains i until a maximum slew slewmax within the voltage domain i exceeds a defined slew threshold; (b) calculating maximum insertion delay values for all cases for each of the voltage domains; (c) if the maximum insertion delay values for all cases are associated with a single voltage domain j: (i) adding a max size buffer to all voltage domains except voltage domain j; and (ii) repeating steps (b) and (c); (d) reducing buffer sizes for each of the voltage domains; (e) recalculating maximum insertion delay values; and (f) adding parallel buffers to a first level of the voltage domain having a highest maximum insertion delay until the calculated skew across the plurality of voltage domains no longer improves.