Waterproofing a crawlspace as defined means preventing any ground water from passing through the foundation and accumulating in the crawlspace.
Most waterproofing techniques must be applied during the construction of the structure.
Outside perimeter drains, gutters, waterproofing materials on foundation walls and proper sloping of the land next to the structure all need to be considered.
Reality is, in most construction, the proper steps have not been followed through. In this case, water management is the proper term for the control of ground water entering the crawlspace. It may be possible to upgrade the gutters and improve the grade of the land but most often it is impractical to completely prevent water from entering the crawlspace. Landscaping, sidewalks, HVAC units and other items on the exterior of the home make it very difficult to achieve the desired results.
The best approach now becomes water management. Admitting that water is going to pass through the foundation and controlling it so it is no longer a concern.
A properly installed interior perimeter drainage system with a proper sump pit and sump pump discharging to the exterior of the crawlspace is mandatory for the control of water entering the crawlspace.
Even if the structure has water entering only every five to ten years the drainage system will be there to eliminate the destruction its effects can have.
Think of a drainage system as an insurance policy for your crawlspace!