5 of the 6 Components to a Dry Basement have to do with Drainage

The World of Concrete trade show is awe-inspiring. The thing I like the most is getting to listen to some of the smartest people in the world talk about how to build better with concrete.

February 26th I got to listen to Brent Anderson from Brent Anderson Associates, Inc. speak about residential waterproofing. Brent is a well-known expert on basement construction and waterproofing.

Here are the highlights of what I learned:

5 of the 6 components to a dry basement have to do with drainage:

1. Positive slope away from the foundation- this gets the water away from the basement quickly.
2. Use clay cap for the last 12"-16" of backfill at the top. The clay is not very permeable, so it sheds the water versus sending it right down the side of the basement.
3. Use a free draining backfill- water that somehow gets through the "clay cap" should perk right to the bottom of the backfill into the drain tile- not sit in poorly draining soil causing hydrostatic pressure.

Did you know that fine to coarse, clean gravel drains 23 feet per minute? On the other hand, silty sand drains 5 feet per month. Why have the pressure on your basement walls build up so much do to poorly draining backfill?

4. Properly installed drain tile and aggregate. Brent suggests drain tile on the outside of the footing and the inside- tied together with a sleeve running through the footing.

Keep the drain tile towards the bottom of the footing- particularly in areas where the ground water is high. Don't put the drain tile up at the interior slab height- by the time the water is backed up to that level problems may have already started and you have a wet basement.

5. Have a water discharge system- A sump pit or drain tile that discharges to a lower elevation. He suggest building a sump pit even if you don't think you need one. You don't have to buy a pump for it- but would have the option of installing one later if needed.

6. A waterproofing membrane properly applied.