A basement or below-ground garage faces a type of damp that terrace or roof waterproofing never encounters: the hydrostatic pressure of groundwater pushing against the wall or slab.
Why just any system won't do
A system designed for surface rainwater (without sustained pressure) may not withstand the constant pressure of groundwater, especially in areas with a high water table or during prolonged heavy rain. Choosing the wrong system is the most common reason a "waterproofed" basement still lets water in.
Positive or negative waterproofing
"Positive" waterproofing is applied on the outer face of the wall, in direct contact with the ground, and is the most effective because it stops the water before it can pass through the material. "Negative" waterproofing is applied on the inside, when digging outside isn't feasible (already-built basements, party walls), and works by retaining the water that has already partly passed through the wall, being generally less definitive than positive.
Perimeter drainage: the complement missing from many quotes
Besides the waterproofing treatment of the wall, a perimeter drain (with drainage sheet and a drain pipe connected to a discharge point) reduces the water pressure that ends up hitting the wall, greatly improving the overall result compared with treating only the wall's waterproofing in isolation.
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