In the middle of the crawlspace floor area on top of the building pad we place a perforated drain pipe with gravel and cover it with filter fabric.
The perorated drain pipe is installed with a T-fitting to connect a surface drain for the finished concrete floor of the crawlspace.
The 3" drain pipe from the floor drain to the outside of the foundation wall is non-perforated and sloped so that any surface water from the crawlspace floor from a severe plumbing leak or flood ...or good hose out ...will drain to the exterior where it terminates in a dry sump fifteen feet away from the house.
A 3-4 inch layer of drain rock is then backfilled into the entire crawlspace.
Any bulk water intrusion whether flood or otherwise will quickly drain out.
The crawlspace is now ready for a sturdy vapor barrier.