Regulations change over time, this home's bathrooms are all interior, with fans to evacuate moisture, and the toilets accordingly have internal overflow†, both these features were not legal when my parents home was built.

† Historically for a residential toilet in the UK if the water rises above the intended maximum level in the tank, it just runs into a pipe to the outside of the building, in principle you can now see what's wrong and it's not dangerous... but, if you don't fix it promptly this results in a stain on the building exterior, as well as potentially wider water damage, plus it can freeze in mid-winter which isn't good. But wait, a toilet has a very obvious place to dump unwanted water, it's connected to the sewer and if that is broken you've got much more serious problems. So a modern toilet tank just re-uses the flush mechanism to dump excess water the same place as everything else. This elegant solution, already needed in some commercial applications, was I believe made legal in newer residential building regulations maybe in the 1980s.