Foundation wall drainage
bryanw511
| Posted in Green Building Techniques on
To create better drainage, I’m considering extending the aggregate from around the drain tile up the foundation/basement wall closer to grade instead of just using regular soil backfill. I can’t find much info regarding this technique online. How is this accomplished? How close to grade is the aggregate brought, and how wide is it in the trench? Trenches are a couple feet wide; that’s not all stone, right?
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Replies
Bryan,
The standard advice here at GBA -- for example, the advice for a new-construction basement in my article, "Fixing a Wet Basement" -- is as follows: "Install a layer of dimple-mat drainage board installed on the exterior side of the foundation walls; failing that, the foundation should be backfilled with coarse, free-draining material like crushed stone, topped with an 8-inch layer of dirt (ideally, dirt with a high clay content)."
Not all sites need free-draining backfill. If the local soil is sandy, it may drain well. If you have to haul your backfill from a quarry, it can get expensive, especially if the excavation hole has sloped sides. Backfill costs will be less if the excavation is relatively small, and the sides of the hole are close to vertical. (Of course, such holes are dangerous to work in, but that's another story.)
If you want to minimize the volume of the expensive backfill, there will be some hand work, with alternating loads of free-draining material and dirt from the site, placed with a small bucket or laborers with a shovel.
If the excavation is cheap, and you can afford the backfill, a dump truck from the quarry can just backfill with nice free-draining material, and you can cap the backfill with high-clay soil.
I use sand on top of the fabric over the drain tile aggregate when site backfill is unsuitable, drains great.