Does my PRV setup need a backflow preventer?

[TCP]

Hey looking to install a PRV in my home but not sure if I need a backflow preventer. I get around 80-90 psi street pressure coming into the home. Looking to put in a PRV and drop it to around 50-60psi. However, when the sprinklers go off it drops to around 60psi coming into the house (had a gauge on a hose bib). So if I set the PRV at 50 lets say would I need to the BFP? Basically my question is if the house pressure is 10psi or less, greater than line pressure when the sprinklers are running will the BFP be necessary? I have a BFP on the sprinkler side but thats a separate branch off the main. Right now my expansion from my hot water heater goes back to the street but I did install an expansion tank when I put in my new hw heater for this future install. Looking to put in a Watts 25aub-z3 PRV.

 

[Jadnashua]

Code still requires the backflow preventer on your sprinkler system. Some people tap off for that prior to the PRV to provide maximum pressure to the sprinklers. Adding a PRV does entail adding an expansion tank in the house as well.

 

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[TCP]

Yes I have the expansion tank already installed. So will I need a BFP for the house domestic line with the PRV?