pre-existing

A garden tub can be installed in a pre-existing bathroom. You have to remove the pre-existing bathtub and install the garden tub.

"pre-" means before, so pre-existing means to exist before (something), or to procede. For example, there were already pre-existing symptoms when the doctor diagnosed the disease. Or, fast food stores that pre-existed McDonalds.

No. Homeowners insurance does not cover un-repaired, pre-existing conditions.

You are thinking that some conditions are considered "pre-existing" and others are not. That's not it. Did you already have the condition before, say, applying for insurance? That's the idea of pre-existing.