In the past we have heard people complain about cold rooms on the North side of the house.  It's never an insulation factor, because I inspect all installations as well as the building inspector.  Not that we are infallable, but the chance that we both miss it is zero.  Builders have been forced to make the homes air tight but air has to flow in through the insulation and that air is what keeps the house warm.  The key is to keep it in the wall as best as we can.

What we are doing to reduce those complaints however is using high density insulation in the walls and the ceilings.  We always caulk where the 2 x 4 touches the floor ply and the seam that runs vertically where the walls join in the corners.  We use foam insulation in between the window and the framing and we put in high efficiency electrical boxes that blocks most of the air that flows in the walls.  We are also trying to run 2 - 6" heat vents to rooms that may be more susceptible to the cold air.  All vapour barrier joints are taped - not just overlapped and stapled.  All exterior tyvek is carefully inspected and sealed around all openings, cracks, and crevices.  We also inspect and seal around any mechanical piping that goes through the exterior cladding.  We look for any places where air might get in and do what we can to stop it there.

The doors in the colder rooms must be left open do improve air flow.  That will keep them warmer.  Also, after a few years you may have to top up your attic insulation as it settles quite a bit.   A celing fan on the second floor to help push the air around works well too.  Be aware that the "draft" you are feeling is not convection currrent whereby the warm air and cooler air meet and makes it feel like there is a draft. 

Please read the maintenance manual from the warranty program and don't be afraid to do what they suggest.  It won't void your warranty.