Will the pipes freeze?

Not in a properly designed system. The IRC requires protection for water piping exposed to freezing conditions, and both the IRC's residential sprinkler provisions and NFPA 13D specify how. In a Colorado home that means accounting for exterior walls, attics, unheated spaces and anywhere else piping could freeze. These risks must be addressed during design, not afterward.

No water-filled system is immune to an extended loss of heat or an improperly protected pipe. Seasonal homes can be winterized, but the sprinkler system needs its own procedure, coordinated with the domestic plumbing. Homeowners should not shut off or drain a sprinkler system on the assumption that it winterizes the same way as ordinary plumbing.