Drip irrigation system - some plumbing and design questions

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Denver, CO
Hey all,

I am putting in some drip irrigation and hose bibs as part of a landscaping project, where we will have orchard, vegetable gardens, flower gardens, edible landscaping throughout, and aesthetic landscaping.

I have a lot of technical and design questions. I probably won't get answers to all, but meaningful input on any is helpful, and value your recommendations. Thanks so much!

This is drip for gardens, landscaping and hose bibs, but there will not be any watering of the grasses.

- Have the system be able to fully drain by gravity
- Design the system so that it can tolerate light freezes overnight. Here in Colorado, we get intermittent light freezes in the early fall and the late spring, surrounded by many warm days - want to minimize required effort during those times.
- Provide regional access points for the 4 drip irrigation zones (daily, every other day, weekly, monthly), from which shallower 1/2" lines can be run to groups of bushes, etc
- Have 2 frost-free yard hydrants and 2 seasonal hose bibs

Relevant Info
- NW corner of the lot is the low point. Slope direction shown on diagram.
- City water supply (around 60 psi) feeds the home, with the meter in the NW corner (near street; valve shown) and running along the west edge of the lot, beneath the ditch, and continuing south to the home (300' run)... currently 1" copper, but is under spec'd and needs to be upgraded.
- Diagram shows a single line, but where irrigation access points are shown, assume
- Backflow preventer will be used.
- FF yard hydrants off supply line to house. Seasonal hose bibs off irrigation valve.
- On 2015 IPC

Technical Questions
1. Aside from an expensive sanitary frost-free hose bib, are there no-maintence-during-light-overnight-freeze options for a hose riser that will be code compliant (no electricity available)?
2. For the seasonal hose bibs, is a sanitary yard hydrant required by code? I know that they are here, when tied directly into the water supply feeding the home... unclear if required off of the irrigation system w/ back flow preventer. Safe ideas welcome.
3. Will 100psi poly lines (without fittings) tolerate an occasional short belly that will freeze/thaw a few times each winter? Just gauging how 'perfect' my grade has to be.
4. For seasonal hose bibs and watering edibles, should I be using NSF rated poly? If so, I see the local supply house has a colored one that is NSF, but calls it HDPE, not 'Poly' as the others are. They also have one that is labeled glossy, but I'm not clear what that's about.

Design questions
5. Should drip zones be run with 1" poly, or downsize to 3/4"? Scale on diagram.
6. What's the minimum burial depth these should be 5 parallel run poly pipes in a trench? I was thinking of 8"(versus running under the shrubs) for light freeze protection. I do have a sub compact tractor that will traverse them (assume 2500 lbs), but pretty soon it won't be going in this space often.
7. Given gravity drain and light-freeze goals, what's the best way to surface the drip zones? I was thinking of placing a 6" deep valve box over the 5 parallel lines, with a threaded tee pointed upwards from each line. Then I have an option of going out the side of the box with 3" buried 1/2" line or a short section of poly to a riser just outside the box.

Overview diagram
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Not addressing your questions, but HDPE stands for High Density PolyEthylene.
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