I've dug out a trench around the perimeter of my crawl space. Then I planned the next steps. I took a week off but I'd like to finish this project next weekend.

I'm going to put a 4" perforated pipe. But my question is about the necessity of backfilling.

The trench is as low as the bottom of the footing, at least a foot deep from the top of the dirt and about a foot and a half wide. We kinda had to dig wide for us to be able to walk. But now I can see how this may have been an overkill since I have to fill it with gravel. That's going to be a lot of gravel! Something like 250 ft3!

So the question is do I really need all that gravel? Do I need any at all? Can't I just put a pipe wrapped in garden fabric?

I'm also considering using NDS EZ-Drain although it's quite expensive at $45/10'. If I use that, it's not going to fill the trench. So again do I need to backfill with gravel?

What's the purpose of the gravel in general? I can understand how gravel is better than soil to allow the water to flow, but isn't an empty space even better?

2 Answers 2


I had to think about this one for a bit. The real reasons for a porous backfill are to easily track water, give depth to protect drain tile from freezing, and keep it in place so it won't float in the water. As long as those goals are met you should be fine.

  • 2
    Thanks! Not sure what exactly mean by "track water" but sounds like as long as I manage to prevent the pipe from floating I'll be OK without gravel.
    – Peter Q
    Jan 24, 2011 at 15:04
  • 1
    Be a sport and at least cover it with few inches of gravel or crushed stone. LOL Jan 24, 2011 at 15:54

In addition to @shirlock's answer:

  • Gravel doesn't compact much. If you fill with soil to grade level today, in a year you'll have a shallow trench.

  • Gravel supports the load of traffic, distributing and dispersing it, so your drain tile won't collapse.

  • Gravel gathers water from a wider area, keeping things dryer. (Soil that doesn't percolate well will hold the water instead of giving it to your drain).

Coarse sand also has these desirable properties, and is easy to hand-shovel, but is probably more expensive.

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