Herniara Glabra as ground cover - How deep are its roots?

[mgpell]

We are looking at Herniaria Glabra (rupturewort) as an option for ground cover for our roof garden. Does anyone know how deep its taproot can reach and if it is considered as an aggressive plant in that respect? We need to know this so we determine if a root barrier is required to stop the roots reaching the insulation layer.

Thanks a lot

Micki