[greglepore]

I had a house on a slab here in Va for 3 years with late 90's Shell poly pipe in the attic-forget the name but its considered weak-and it was fine for a spell of a week in the teens a few years back-the air handlers in the attic kept it warm enough. If you're worried, let a faucet or two run very slowly at night.
However, did learn the hard way that mice get in in the cold and love to eat pex type pipe. Mine came in thru a external chase (think gutter alu pipe) that the freon lines ran in. Installers filled it with expanding foam, which the mice went right thru-should be filled with the stainless wool that rodent control guys use. Had numerous leaks in ceiling over Christmas week. Joy to the world.