How to fix depth issue in faucet stem?

Question

I started renovation of bathroom myself. Instead removing the old drywall and then put a backerboard, I installed backboard on the top of old drywall. This made the stem shorter. I tried my best to maintain the length of stem that is outside of wall so that everything works fine.

So the problem now is that the stems aren't enough out of wall. Therefore I cannot screw the trim kit and faucet handle. The instructions called for more length outside of wall, It is approximately 0.5 inch short. There is no give from the back side of the wall, but I do have access.

I don't know how to approach this problem. Any idea what can be done?

Can I buy different trim for Pfister model which needs shorted stem out of wall? Or can I buy stem with longer length? Could I find stem extension kind of thing?

Thanks in advance.

The white thing in photo is the drywall compound that I stuck there for strengthening old drywall.

Answer 1

Since you've indicated that you have access to the back side of the wall, my answer is to move the plumbing. It doesn't sound fun or easy, but it shouldn't be too bad. Use grinding and drilling tools to carve out the framing and drywall as needed, then shift and re-secure the plumbing.

The 1x4 down low may not even be a problem. I'd bet that the two 1/2" copper lines will flex enough. Otherwise, you could use pairs of 45° elbows to pull in above it.

I don't see much holding you back from shifting the valve assembly forward other than some drywall mud. Get to it!

Answer 2

A stem extension kit might work. Without seeing the trim I couldn't say for sure.