Turer to the general contractor or building manufacturer.
Roof curb installation.
Curbs should be a minimum of eight inches above the finished roof and factory insulated to reduce condensation.
This type of curb has the added benefit of being able to be installed either during the roof installation of after the roof is finished.
Placing the curb on and attaching it to the ribs also allows better transitioning from under the roofing on the upslope end to cover the roof on the downslope end.
A canted curb for example should be used for a built up or modified bitumen system roofing system.
Curb installation should be a part of the roof deck not on top of insulation or roofing materials.
And installed by an experienced erector.
First the basic design of the curb should take into account the roofing components so that it can be properly flashed into the roof system.
Roof curbs should be supplied by the hvac manufac.
Contractors should not be asked to supply or install roof.