Read the soil report before you choose the waterproofing
The tanking specification is decided by groundwater chemistry, not by the architectural drawing. Here is which numbers in the geotechnical report actually change the build-up.
01The two numbers that matter
A geotechnical report runs to dozens of pages, but for a below-grade waterproofing decision two figures carry most of the weight: sulfate concentration in the groundwater, and chloride concentration. Together they place the structure in an exposure class, and the exposure class sets both the concrete and the membrane.
In the Eastern Province those numbers are frequently high enough to move a project two classes above what a standard detail assumes. Sabkha ground near Jubail and Ras Al Khair can carry sulfate levels well beyond the XA3 threshold, and chemistry varies sharply over short distances. A report from the next plot is not a substitute for your own.
02What changes as the class rises
At the mild end a single bonded membrane is adequate. As the class rises the build-up gains a second layer, then a protection board installed before backfill rather than after, then a crystalline system working with the concrete rather than only on top of it.
The detail that most often fails is not the membrane itself but the junction: construction joints, service penetrations, the kicker at the base of a wall. Waterstops and hydrophilic strips are cheap relative to the cost of finding water in a basement two years after handover.