SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

If you are on city water, you need to check with the city to determine what BF might be required by LAW and who might be required to install it. Some places don't mind if you install it, others required certified plumbers.

There can still be government regulations that might (or might not) dictact what should be used (i.e. local building codes). There's a wide range of requirements. I think in most of Illinois, a certified plumber is required to at least oversee the ENTIRE instillation of a sprinkler system, other places require a building permit and a certified plumber to at least to the instillation upto the backflow preventer, and then there is where I live where the law only states that a backflow preventer of some sort be utilized (but the homeowner is free to do all the work himself).

If you're free to use any, then you have to decide which is right for you...

#1) PVB - Cheapest, but it has to be installed outdoors about 1 foot higher than any of the spray heads.
#2) Double Check - Next highest in cost. Can be installed inside/outside, above/below ground and above/below the level of the spray heads (you can place it anywhere because there is no discharge to worry about). Some do not consider it to be a safe enough device (especially if you are injecting anything into the water such as fertigation) because of the possibility of failure such as any trash in the water getting stuck in the device and preventing both check valves from properly sealing.
#3) RPZ - Most expensive and safest (I think "failure" mode is to discharge water all over the place rather than letting it backflow), but must be installed 1 foot above grade (or installed in such means that it is impossible for the device to become submerged).

Can I add a vertical double check in the basement (no need to winterize). I would also like to add fertilizer after the double check. Are there any issues I should be aware of?? Thanks!

Adding fertilizer means having an RPZ, if you want to cover all bases. It will take away over 10 psi from the system pressure, so you may have to rework the system coverage. Install a RPZ outdoors, a foot above grade, and follow its instructions carefully, come wintertime, if your pipes are subject to freezing.