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Old 03-21-2012, 02:23 PM   #1
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slope away from walk out basement area


I'm working on a crushed stone area that will be directly outside of my walk out basement. The contractor is proposing digging down to 8" below the current level of my basement door's cement sill, then filling with 4" of crushed stone. That would give approx. 4" step up from rocks to top of sill (on top of this cement sill is the aluminum threshold for the door, so the step would be more like 5-6" from the top of the rocks).

I believe that digging down to the 8" mark will be right around the point where the footing and foundation block wall meet, I base this on the fact that my basement door's cement sill is essentially a CMU block, so I assume about 8" tall. This concerns me because I was thinking that where foundation wall and foot meeting is a vulnerable point for water infiltration... Should I look into going a bit further down with the digging, or is it not necessary? The house was built in 1949, it's a block foundation and the drainage in the yard is generally on the poor side with the potential for seasonally high water table.

I am telling the contractor that under the crushed stone I need at least a 5% grade within the first 5' from the foundation and then at least a 2% grade from there. The area we're filling with stone extends about 12' from the foundation, so this would be about 3" of drop over the first 5' and then another 2" drop over the next 7', a total of 5" drop over the 12' of distance. The entire thing would then be filled with ~4" of crushed stone which would be approximately level. The idea is that it gives easy drainage and is a basic spot to store some tools and maybe keep the BBQ grill.

Is this amount of grading reasonable and necessary, or if it not as critical when you are essentially below the level of the foundation meeting the footing (which I believe I will be almost immediately)? Is it even reasonable or possible to achieve a 5" grade over 12' when you're just a local carpenter hiring out the excavation, or should I be pushing for something more aggressive to ensure it's met?

At the 12' mark (away from the foundation) the existing yard is probably about 10" higher then the current door sill, meaning the difference between the area we are proposing to dig and the existing lawn could be about 24" now with this grading. It may be possible to knock the existing lawn down a few inches, and there is the ~4" of rock which will be present, but overall we still have about an 18" or so difference that need to be accommodated. Rather than building a short stone retaining wall with a step or two, what I'm considering is tiering the area over about 6' using 4x6 PT timbers or something similar to create giant steps. I was thinking that if I started the "steps" at an 8' distance from the foundation and completed them at about 14', that would give me a total of three 2' wide tiers/steps to work with, so each tier would need to accommodate about a 6" rise to match the dug out area to the existing lawn level. Assuming I did 2-3" of crushed stone on each of the "steps", what sort of grading would I want on each step? Would it even matter, or would it be sufficient just to get it to eye ball "level" and not worry much about trying to pitch them?

Also, does any of this make sense, or did I just ramble on for 10 minutes?

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