Exposed rock on the surface of french drains
When constructing a french drain groundwater removal system that you count on to pull rainwater away from your foundation, resist the common emotional arguments associated with the desire to cover up the rock left open on the surface.
This method is used for maximum groundwater collection when it rains hard. A common statement I hear is “my kids will toss rocks”, or “I don’t like the look of exposed rock”.
If you subordinate these contentions to the health of your hand excavated french drain, you will be pleased in the long run with no home drainage problems, and a groundwater free, healthy home, free of mold and moisture accumulation in crawlspaces and basements. I cannot stress this enough.
The rock is open on the surface of a properly constructed french drain groundwater removal system for the reason that during hard rains, this is required to collect the groundwater next to your foundation, or overflowing from filled gutters.
A layer of weed cloth is placed shiney side up approximately 4″ under the top layer of the rock to protect the french drain from clogging with debris. Rake leaves off the rock or spray them off with the hose away from the foundation periodically. Do not let landscapers cover them with barkdust, or dig into the sides of them for planting, or to do other landscape projects.