Insulation and trace heating for plastic water pipes

Hello,

I have set up an apartment above the garage. For this, I had to lay a water pipe from the house. It is made of plastic (32mm), laid underground, about 120 cm deep. Now, the pipe freezes in winter. I assume that it is the connection from the house and the entrance to the garage that freeze. I insulated it with a plastic pipe filled with construction foam. I know that is not insulation and I apologize for my stupidity. So now I want to do it properly. I have to dig again.

The connection from the house and the entrance to the garage are quite close to the outside wall. In the picture, the entrance to the garage can be seen. The wall at the back is the garage wall. The connection from the house is the same.

My question is, which insulation made of which material and with what thickness should I use for insulation? Should a trace heating be installed as a precaution? If yes, which one... with a thermostat or self-regulating? Which is suitable for a plastic pipe?

Thanks in advance for the answers.

Regards from scxx72