When installing artificial grass on hard surfaces i.e. balconies, paving, concrete. I would recommended installing the grass onto a drainage layer, for example drain cells, shock pads, basically any product that has a vertical and horizontal drainage aspect.
For grass areas fully exposed to the elements, will require the best possible drainage, the system I would use is drain-cell & geotextile.
The other reason for having a drainage layer / underlay it will make the grass fibres stand up straight longer because the softness the layer causes takes the stress off the fibres just like a carpet underlay take the stress off the grass fibres helping the grass fibres to stand up straight longer with a softer feel underfoot.
Which ever system you use, I would recommend laying the it loose and infilling the grass with double the amount of infill sand. If you require the draincell to be fixed and if possible, you can create a wooden frame on the edges of the grass and screw the draincell to the frame, and secure the frame to the surrounding wall.
