I recently purchased a house by Lake Erie which has a crawlspace foundation. There are existing drainage trenches throughout it dug into the hard clay, which all drains to a sump pump. These trenches are not maintained, and have built up over time with debris and now have standing water.

As part of my renovations, I plan to lay down a moisture barrier and seal the crawlspace as best I can. I was recommended to fill the existing drainage trenches with crushed stone, but after getting a quote for how much that would cost I am now wondering how necessary that is. What are the downsides of just leaving the existing trench system, and laying the moisture barrier over top of it? The crawlspace would be almost never accessed.

1 Answer 1


I think you want to insure good drainage under the plastic sheeting. I don't think it's a good idea to leave the channels to fill or to collapse.

At some point work in the crawl space might be required to repair plumbing and hidden channels under plastic sheeting might cause problems.

Flexible porous plastic drainage pipe in the existing channels might be a better solution than crushed rock. It would be very lightweight and easier to install.

I have seen advertisement for porous rubber block system that claims this system to be superior to "French drains". These blocks would presumably not need filling on top, but might be stiff and hard to get into the crawl space.

Both of the above would probably require the channels to be cleaned out and maybe deepened a little.

  • So the only real downside is the channels will eventually fill and collapse, which could cause plastic to slip and become inconvenient when working down in the crawlspace?
    – Rachel
    May 1, 2019 at 15:17
  • 2
    Nope, the danger is that you will have water pooling under the plastic and create possibilities for it to migrate into the house. The water is coming through the soil, the plastic barrier will help with dampness but you really want to drain that water out of the area. That is the purpose of the sump and pump. You really want to help the water leave as fast as it can rather than relying on the moisture barrier alone.
    – Ukko
    May 1, 2019 at 15:46

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