Building a 600 sq ft ADU on Piers in Rhode Island Zone 5 – Plumbing/Insulation – GreenBuildingAdvisor

We are designing and building a 600 sq ft 1 br dwelling unit on piers. Goal is to build affordably, energy efficiently, meet code, avoid maintenance disasters. We have worries about burying plumbing in an insulated floor, and the issues involved with a plumbing leak due to frozen pipes, or a plumbing leak from a washing machine or water heater etc.. Looking for ideas to prevent frozen pipes, prevent water traveling along the floor in the case of a leak, and in the worst case scenario make servicing the plumbing possible without ripping apart the house from the inside. Planning an insulated chase with conditioned air coming up from the ground for bringing water in and sewer out that would be accessible in the floor of a closet next to water heater.

Some ideas: 

1 – Have two distribution manifolds one for hot and one for cold in the insulated chase from ground and run 2 or 3″ pvc from there through the floor to each fixture, then pull Pex-A through to each fixture. The PVC would be open at both ends, and above the floor at the fixture, so that conditioned air can get to the pipes, if there is ever a leak water drains to the insulated chase and to ground without getting into the floor system, and pex could be replaced without any floor dissasembly, also no fittings in the floor system. – Not sure this would be allowed by code though. 

2 – Dedicate one or two joist bays in the floor system for plumbing and leave a 2″ air space above the insulation water to run in, venting to interior conditioned air.

3 – Drain entire bathroom floor including washing machine to contain a leak to just the bathroom area, and make the sheathing under that part of the floor system more removable (screwed up 1/2″ ply or zip R instead of nailed)

Are there any tried and true methods of dealing with plumbing in an insulated floor in zone 5 and colder?

Thanks