What sort of renos did the contractor do to the house? Did they remove any walls on the main floor? Are you sure that it is just the plywood moving and that the joists are moving (deflecting) as well? Did they pull any permits for the work they did? You can find this out yourself by going to
http://calgary.ca/myproperty , plugging in your address, and checking the section labelled "
Building Permits (active or issued in the last 3 years)"