Typically when building a home, a drainage system is necessary around the perimiter, in order to move ground water away from where the footings meet the foundation, in order to to stop water from coming in the house.
When we began excavating one of our projects, The Brody Spa, we ran into more water than usual. In this situation there were two reasons for so much ground water;
1) We were at the bottom of a mountain
2) We hit ledge at 8 ft and most of the hole was inside of a big rock with no where for it to drain so it filled with water.
We realized if we didn’t come up with a solution we would not be able to pour our footings, and consequently the foundation and rest of the house.
Our in house design team quickly came up with a fix: A two layer sub drainage system consisting of; an underslab drainage system, and a sub footing drainage system. The upper layer consists of perforated pipes at the footing level in a bed of gravel to drain the water and protect the under slab. The second and lower layer has a perforated pipe running below the footings and out to drainage to day light. This was neccessary to clear the water away and keep it out of the way so that we could pour the footings. Between both systems we made sure there would be no capillary effect or wicking of water into our slab. You can see both layers below (designed in sketch up by Glenn Callahan and Gabe Solberg):
The diagram below shows the sub footing drainage system at a pitch which takes the ground water to drainage to daylight:
This diagram shows the under slab drainage which is at the level of the footings in a bed of gravel:
There are perforated pipes running at a pitch to drainage to daylight.
After this system is installed, we then used EPDM (a type of synthetic rubber) combined with butyl tape to create a water proof barrier underneath the slab to stop wicking and any other chance of ground water getting in:
When all is said and done the water drains away from the hole and clears into drainage to daylight:
Check out part 2 to see what the drainage system looks like: Click here
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