Welcome to the Bunnings Workshop community. Thank you so much for joining us and sharing your question about what tube size to use for your home irrigation system.
I recommend using the 13mm pipe size. It is the most common size used in irrigation systems. It offers you flexibility and allows you to go smaller or bigger without adding too many pieces. I find that irrigation systems are in a state of constant change. As time moves forward, so do the number of plants we possess. By adding more plants, we, therefore, add more pipes to our irrigation system.
The 13mm pipe has more tolerance for dirt and debris in the line versus a 4mm pipe that could get clogged up if a sufficient amount of dirt got in the line. You can directly install accessories on a 13mm pipe. Common fittings sich as elbows, joiners, and drippers are made to fit in a 13mm pipe. If you need to use a smaller pipe, I suggest using it sparingly and only if it is necessary.
I suggest drawing your proposed pipe layout. This will help you determine the pipe length that you will need, plus the number of joiners, connectors, and elbows you will be using. My number one tip for your entire assembly is to install a Holman 13mm Pressure Reducer And Filter Assembly. This sounds like an excellent project for spring. Any updates you can provide while building your system would be much appreciated.
Please keep us updated with your progress, we look forward to seeing your irrigation system up and running.
If you need further assistance, please let us know.