Flowable fill is being used in Canadian municipalities as a select trench backfill under urban streets subjected to heavy traffic loads. The flowable fill mixture being sold by the Canadian ready mixed concrete industry for backfilling utility trenches has been found to be a good structural fill in supporting the overlying pavement and, in some cases, has been used to physically support buried utilities. The high thermal conductivity of this material has been found by some municipalities to contribute to a deeper frost penetration when used as a trench backfill. This deeper frost penetration has caused hydrant laterals and water service lines to freeze as well as differential frost heave of the asphalt surface surrounding the trench. This paper discusses these problem, presents some results from a full-scale experiment in Edmonton, Alberta, and suggests some potential solutions.