San antonio is a temperate climate and it rarely gets below freezing and i know pex is more resilient when is comes to freeze ups as the plastic tends to expand as needed.
How to run pex through attic.
When running pipe from a slab to an attic use cross linked polyethylene tubing or pex instead of copper.
It may give it an extra hour before it freezes solid.
Pex is semi flexible which allows for long continuous runs through joists and studs.
Do your best to separate the hot and cold lines to minimize heat transfer.
I would re route it into the attic and down to each fixture.
For a variety of reasons from pipe damage under a slab to home design constraints water pipes may need to be run or rerouted through a home s attic.
Be sure to leave extra pipe on both ends of the run.
Insulation only slows the time when it will freeze after the water is not running through the pipe.
Secure the line to the joists using clamps image 2.
Pex c is the most economical choice with a 10 foot section running 1 75 to 3 50 depending on brand and diameter.
Pull the lines up through the holes drilled in the sub floor image 1 and then run the other end to the area where the water will be coming into the home.
I looked in the attic and noticed that all of the plumbing that once was in the slab had been replaced by pex and was now in the attic.
Pex type is forgiving when it freezes as far as breakage but insulating an exposed water line does little to keep it from freezing.
Best case imo is to use continuous runs of pex with no fittings in the attic so your plumber will have to plan the layout a bit and the pipe should be very well insulated and protected from damage so that people walking through the attic insulation can t step on it.