Are shutoff valves in shower supply lines against national plumbing code? I replumbed my house and installed shutoffs in each of the shower lines for the same reason shutoffs are installed in the other lines. The shower controls have the anti scald feature and a pressure balanced valve. The control instructions say not to install shutoffs on either side of the valve as this may create a cross-flow condition at the valve and affect the water temperature. I installed the shutoffs before I had the shower controls. Most people I know have newer houses and no shower shutoffs, which I suspect for the reason above. In my case, one set of shutoffs is not easily accessible, and I wired tied the handles on the other set to prevent accidental closure.

Hey Shader,

"Are shutoff valves in shower supply lines against national plumbing code?"

Chapter12, Section 1211.3(a) of the Standard Plumbing Code states; "Each individual fixture SHALL have a shut-off valve which will permit each fixture to be shut off without interfering with the water supply to any other fixtures."

Manufactures make shut-off valves a part of the valvebody,(see image).
Look down on the right hand inlet and you will see a AP16213 Screwdriver Stop Assembly. These are called "Integral Stops" and are there to get away from providing a access panel for stops on the supply lines.

With the possible exception of closing one stop and leaving the other open I can see no reason for a manufacture to advise not to install stops on the supplies. (1) it's against code and (2) it just doesn't make sense. Regards, Tom