Compression Fittings Allowed Inside Wall?

Can I use 1/2" FIP to compression fittings to attach 1/2" copper tubing to my Delta universal valve housings for my new showers?
Our Tucson hard water will eventually eat away at the faucet valve housings, and I want to be able to replace the valve housings in the future without major surgery.
I thought about using brass 1/2" unions, but they go for about $7-$10 each, and the compression fittings are about $3 each. It would take 4 unions for each faucet: 1 for drop ear shower outlet, 1 for cold inlet, 1 for hot inlet, 1 to tub spout (or cap the bottom outlet for a shower only).
I thought about using PEX adapters, put I don't know how you would get a PEX crimp tool in the small opening for the valve, not to mention the extra PEX slack you would have to allow for future replacement.
Tucson uses UPC - so I don't know if UPC allows compression fittings, or unions, inside walls.
Thanks

Compression fittings are not allowed in concealed locations.

So, any alternative to compression fittings? Would threaded unions be OK? How would you plumb the valve housing? The escutcheon trim plate is removable, which would allow access to the fittings.
Thanks.

I'd use sweated unions. Or install a water softener. Or both.

Contrary to my line of logic, compression fittings are not allowed but apparently sharksbites are.

So, sweat unions or threaded brass pipe unions would be OK? I'm a little leery about sweat unions - wrench the union to aggressively and you could break the sweat joint?

Would any PEX fittings allow for reuse of the PEX line without cutting it off and adding a coupling (i.e. function as a union)? In other words, can a PEX joint be disassembled and reused without shortening the PEX line? I'm not sure about using PEX inside the plumbed wall, but it looks like the cheapest way if I can reuse the fittings and PEX line to switch out the valve housing in the future. I just don't see how you could get a PEX crimping tool in such a cramped 5 1/2" opening cut in the fiberglass tub wall.
Thanks.

valve

I doubt that Tuscon's water is any harder than Phoenix's and I haven't seen any brass valves destroyed by the water.

So far, I have owned 4 houses in Tucson. Each house has had the valve housings of faucets corroded by hard water. You can replace the valves and the seats, etc., but if the housing is corroded the seats will not "seat" properly and leaks persist. Not a problem for kitchen and vanity faucets, but bath/shower faucets are not as easy to swap out - which is why I want to make replacement easy - without tearing out a wall or tub/shower unit.A water softener might work, but I'm not sure I want the continuing expense of salt and repairs. Tucson water is notoriously hard, and CAP water made matters worse. I can only imagine what will happen when we recylce sewer water for drinking in the future.

fortop said:

So, sweat unions or threaded brass pipe unions would be OK? I'm a little leery about sweat unions - wrench the union to aggressively and you could break the sweat joint?

Click to expand...

Use two wrenches, one on the union nut and one on the outside threaded part of the union and you avoid any tension on the sweated joints.

O.K. - I can make sweat unions work. But 1/2" C x C sweat union is about $6, C x FIP is about $13, and brass FIP pipe union is about $8. So, for not heating up the valve body with a torch, and a sturdier pipe setup, would the brass FIP setup be O.K.? The Delta universal valve has 1/2" male pipe ends on the valve housing - so it could go directly on one end of an FIP union.
Thanks.