Retaining Wall and House Grading Conundrum

by Donald Anthony
(Soledad, CA)

Hello,


I am in the process of trying to create a useable backyard out of a hill. The back yard slopes down directly towards the back of the house. My intention is to cut into the slope an put in a retaining wall. In the newly created 20' x60' area between the retaining wall and the house I intend to put a patio and lay sod. I am at a loss as to how to grade. If I grade away from the house at 2% that is a 4" drop directly into the base of the wall. This would require me to trench down another 9"-12". Should I grade in both directions towards the middle?

Thanks for any help or insight you can provide.

REPLY

Hi Donald,
I understand what you are trying to do, but I am not sure I understand your numbers.

You are correct in grading away fro your house at 2%. Whatever that elevation is becomes the bottom of the wall at the base where you can see it. As far as excavating for the wall goes, you should be able to do a search and find the proper construction drawing showing what is appropriate. This should help somewhat though.

http://www.landscape-design-advice.com/retaining-wall-drainage.html

You will also need drains behind the wall to capture the water coming down the slope towards the wall. You should also be able to find drawings online for this. These drains (running parallel with the wall) should pitch at a minimum of 2% and lead the water elsewhere on your property.

How high the wall should be depends on the elevation at your property line. Try to make the slope not more than 33%. You can figure out that 33% and then you will know the top of wall elevation. The difference between the top of wall elevation and the bottom of the wall becomes your wall height. I think you can figure this out since you knew about the 2% pitch of the area near your house. If not let me know and I'll give you the formula.

I hope this was helpful. If I misunderstood anything, please let me know.

Susan

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Clarification
by: Don

Thank you for your response. I think my question was a little vague. I am worried that if I grade away from the house to the base of the wall water will build up at the front of the wall. The soil here is very hard clay.

Wall Drainage
by: Susan

You need to install a trench drain at the base of the wall. It should be pitched towards one side and the water led elsewhere to a lower elevation on your property in an acceptable area. http://www.landscape-design-advice.com/trench-drains.html

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"Susan,  what a pleasure it was to work with you.  You made me feel like I was your only client - responding late at night and always so quickly!  Your design is amazing and we only hope we can do justice to it when we plant.  You have such fantastic ideas and you are so open to suggestions and changes.  Loved working with you - now if you could only come to Canada and plant it!!!"
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