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Recently, as in September [Final close date was 11/13/2015] this year, I bought a house. This house is on an extreme incline. I would like to level out this incline.

The front first floor of the house sits level with the ground. The property is 120' long and 40' wide. The rear of the property is ~23' below the front of the property. I want to build a wall at the edges while filling the inside until it is level to the front.

I know I have to offset the walls, but what I want to know is with a max of 25' walls slowly turning into level, how much property will I loose. Basically, how much do I offset the walls. I plan to compact the earth as I go along and the project will take place over a few years to help settle the dirt. The final result should be a trapezoid from over head.

In all honesty I considered asking this in Mathematics and Physics since I'm not sure this is reasonably doable. The bricks I'm using are mostly the red ones used to build houses I think 3-5/8" x 2-1/4" x 8". The dirt is fill dirt that I'll be collecting from other sites.

I've done some very basic research, but most of it assumes the wall is a max of six feet.

Edit: I agree with the answers and comments provided. I'm thinking about just building a large porch instead. My main concern regarding the hill is that once I clear the brush away, the hill would erode. Maybe I could use several small walls to make a sort of giant steps?

Update: I did a survey of the area and found that it is kind of a giant hole. Like some huge machine cut the valley out. The walls on the other side are more sheer than my side. It also looks like there was a wall near the bottom of my side of the hill but it gave out maybe 10 years or more ago. The underbrush isn't exactly retaining soil either. I think even grass would be a step up. I'm going to start cleaning the area up after the next hard frost since mosquitoes are still around the area despite one frost. I need a hardy non-invasive plant that will spread out once planted to hold the soil.

Edit2: (Wish I could add comments) If I could get the city to raise two sewer caps or even let me raise them, I could fill in the valley. I'd need about 20,000 cubic yards of dirt. I can get the dirt [shipping would be expensive], but the city won't even let me fix a side walk out front so, it's a no-go.

migrated from gardening.stackexchange.com Aug 12 '15 at 20:31

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  • So grade is 23' over 120'? – Wayfaring Stranger Aug 12 '15 at 20:38
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    BTW, a sketch would be a great help here. – DA01 Aug 12 '15 at 21:11
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    I think you'd be better served having a single wall, and having it professionally built. It would provide you more useful space, and would probably still be cheaper than building 6 or more smaller walls. – whatsisname Aug 13 '15 at 0:01
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    I work with the engineering groups that design retaining walls for a living, professionally. You are proposing both not a small task and a risky task. I have personally been out on several project sites that the retaining wall was either built by a homeowner or a contractor without considering the soil strength. They failed, sometimes in spectacular ways. Global stability is something big that is a worry with projects of this size that you could not just have a retaining wall tip over or crack, you could cause excess weight on the base of the lowest wall which would cause the ground to heave. – Dopeybob435 Aug 13 '15 at 13:19
  • You really need a geotechnical engineer to help you figure this out. This is not a homeowner project. Some of the ties that add strength to a wall go behind the wall into the soil 10+ feet. – Dano0430 Nov 17 '15 at 20:27
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Building 23' of retaining walls is not a small task. This is a giant undertaking. So be forewarned. :)

As stormy noted, 4' is typically the height you can go without having to trigger an engineering sign-off. However, some areas may also have a total height requirement as well. Personally, if I was buying a house with 6 levels of 4' retaining walls, I'd want to see an engineers signature before making an offer. That's a lot of land that's being held back.

As for how far you need to step back, the minimum is the height of the wall. So a 4' high wall would need 4' of space between it and the next 4' wall. More would be better.

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    I think in many jurisdictions the next wall up would be considered a surcharge and would require inspections and engineering review. – whatsisname Aug 13 '15 at 0:02
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    @whatsisname is right, but doesn't go far enough. In pure engineering terms it is a surcharge, and anybody trying to retain 23' of earth without using an engineer to design it is at extreme risk of it failing, and failing suddenly, burying alive anyone who's in the wrong place when it fails. OP - please engage a professional to design your wall. – AndyT Aug 13 '15 at 9:16
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I have very similar circumstances. I had a pro come give an estimate. 40k. The height difference in my backyard is 18-20 ft. He told me I would never make my money back and the best advice he could give me is basically pick a spot closest to the house and let's level it. Basically 30 sq ft. Then it was only 4ft retaining wall. The pro would do it 3k ish.

Sounds like you should do step terracing. Maybe 2-4 feet each level, but 2-4 ft from each other.

I'm thinking of decking the whole damn thing.

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You've got a 20% slope which is not a tough incline to work. You need to focus on walls that are less than 4 feet in height. Any higher will cost bucks to hire an engineer and get permitted. I'd go with shorter walls if possible. If you are good with math you should be able to do CUT=FILL. Buy soil/compost to top. In my experience to not figure cut=fill means lots and lots more money and maintenance. Also, you need to be taking in consideration for neighboring properties without causing any abnormalities. Send a plan with what you have, to include elevations and I'll be able to give you much better ideas. Hey, I taught 'Grading and Drainage'...very important stuff. I could use some practice...grins.

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