Retaining wall

Futbalfantic

Well-Known Member
Joined
Aug 5, 2006
Location
Charlotte
So I plan to put in a retaining wall in my back yard. It’s going to have to be a decent sized wall due to the grade. The back yard is approx 90ft wide and 50ft deep. But the grade change is excessive. About an 8ft rise. I want to put in a 4ft wall to gain some patio space as well as flat back yard space. I looked into an engineer but the one I found quickly charges $700 and in what I found for Meck Co the engineer has to be on site for the build, which increases the price.

For that money and the size of the wall I can over build it by a huge margin. Am I missing something here?

Wall is going to be U shaped. Center section approx 30ft wide 4ft tall. Side legs tapering down to grade.
 

kaiser715

Doing hard time
Joined
Jun 1, 2006
Location
Pocket, NC
Can you step it so you fall under code and permit requirements with a lower wall height? Like a 24" wall, go over 8-10 feet, and have another 24" drop?
 

R Q

Well-Known Member
Joined
Apr 4, 2005
Location
Charlotte
For that height of wall, you need some engineering help to a degree but mainly it has to be built right. If you're using landscape wall blocks you should incorporate Geo-Grid into the build , tamp ever so often, build more, add grisd, tamp etc., Those walls also use gravel as drainage. Most walls fail due to the hydro static pressure behind them.
You should visit a Site One store and they will engineer your project to a degree but will give you valuable info and advice. An 8' wall is no small task and you only want to do it once.
I've built them before a while back, I try to mind my own business now, lol
 

Kickdeez

Well-Known Member
Joined
Apr 6, 2010
Location
Charlotte
You're flirting with the threshold height (and code interpretation) for which a retaining wall requires an engineered design and signed/sealed drawings.

The code reads: "Retaining walls that are not laterally supported at the top and that retain in excess of 48" of unbalanced fill shall be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift."

I've seen it interpreted as any wall taller than 48" requires an engineered design. In this instance, you are close, but skirt under the design requirement.

I've also seen it interpreted as any soil behind the wall exceeding 48" would require the wall to be designed. This is how I interpret it, and I believe Mecklenburg County interprets it this way. Depending on where you put your wall, you could have more than 48" of soil behind the wall. If that's the case, I think your wall will have to be designed and have signed/sealed plans submitted to plan review for permitting.

*This all assumes you're planning to actually pull a permit for this work.* What they don't know can't hurt 'em...???
 

jeepinmatt

..l.
Joined
Mar 24, 2005
Location
On the internet
For that height of wall, you need some engineering help to a degree but mainly it has to be built right. If you're using landscape wall blocks you should incorporate Geo-Grid into the build , tamp ever so often, build more, add grisd, tamp etc., Those walls also use gravel as drainage. Most walls fail due to the hydro static pressure behind them.
You should visit a Site One store and they will engineer your project to a degree but will give you valuable info and advice. An 8' wall is no small task and you only want to do it once.
I've built them before a while back, I try to mind my own business now, lol
It's a 4ft wall and the naturally laying hill behind it slopes up to about 8ft total, at about a 30-45 degree angle.
 

Futbalfantic

Well-Known Member
Joined
Aug 5, 2006
Location
Charlotte
You're flirting with the threshold height (and code interpretation) for which a retaining wall requires an engineered design and signed/sealed drawings.

The code reads: "Retaining walls that are not laterally supported at the top and that retain in excess of 48" of unbalanced fill shall be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift."

I've seen it interpreted as any wall taller than 48" requires an engineered design. In this instance, you are close, but skirt under the design requirement.

I've also seen it interpreted as any soil behind the wall exceeding 48" would require the wall to be designed. This is how I interpret it, and I believe Mecklenburg County interprets it this way. Depending on where you put your wall, you could have more than 48" of soil behind the wall. If that's the case, I think your wall will have to be designed and have signed/sealed plans submitted to plan review for permitting.

*This all assumes you're planning to actually pull a permit for this work.* What they don't know can't hurt 'em...???

I’m using heavy block for structural wall. Not the big box blocks.

But yes like Matt said. It’s a 4ft wall with a (current) heavy slope up to 8ish feet. If my grading guy ever shows up I’ll have an idea what the grade change will be. [yard from the property line goes up a foot or so. Then slopes down towards the house.] So big project. Renting a mini skid and plate tamp for infill.
 

jeepinmatt

..l.
Joined
Mar 24, 2005
Location
On the internet
The code reads: "Retaining walls that are not laterally supported at the top and that retain in excess of 48" of unbalanced fill shall be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift."

I've seen it interpreted as any wall taller than 48" requires an engineered design. In this instance, you are close, but skirt under the design requirement.
If I were building a retaining wall behind my house that can't be seen from the street, and can't be seen from the neighbors, I certainly wouldn't mention it to the local jurisdictions.
 

awheelterd

Well-Known Member
Joined
Oct 18, 2007
Location
Kenly, NC
If I were building a retaining wall behind my house that can't be seen from the street, and can't be seen from the neighbors, I certainly wouldn't mention it to the local jurisdictions.
I don't care if it's beside i40, I'm not calling those bloodsuckers for landscaping
 

braxton357

Robot
Joined
Apr 6, 2005
Location
Morganton
That really isn't a tall retaining wall at all and truly wouldn't even require grid or tie backs, but building it stronger is usually the better option. NC building code straight from the book says "Retaining systems providing a cumulative vertical relief greater than five feet in height within a horizontal distance of 50 feet or less, including retaining walls or mechanically stabilized earth walls, shall be designed under the responsible charge of the registered design professional". That being said, in Morganton at least if you keep your wall at 4' or less they don't say anything. I think you'll be ok.
 

Futbalfantic

Well-Known Member
Joined
Aug 5, 2006
Location
Charlotte
That really isn't a tall retaining wall at all and truly wouldn't even require grid or tie backs, but building it stronger is usually the better option. NC building code straight from the book says "Retaining systems providing a cumulative vertical relief greater than five feet in height within a horizontal distance of 50 feet or less, including retaining walls or mechanically stabilized earth walls, shall be designed under the responsible charge of the registered design professional". That being said, in Morganton at least if you keep your wall at 4' or less they don't say anything. I think you'll be ok.
Isn’t there something in there about surcharge within x distance of the wall. And slope too the wall?
 

braxton357

Robot
Joined
Apr 6, 2005
Location
Morganton
,
Isn’t there something in there about surcharge within x distance of the wall. And slope too the wall?

Only if there's a structure above it. Meck county uses this same code verbatim.
20220805_152539.jpg

20220805_152549.jpg
 

Loganwayne

#BTL
Joined
Feb 15, 2013
Location
Clyde, North Carolina
Call your local concrete plant and see what blocks they pour, as most pour some kind of blocks with the extra concrete. Scm here doesn't do any "architectural" blocks just plain 2'x2'x4' blocks but another company in asheville pours hollow fill blocks that have a rock finish on one side. Either of those options could be done with two layer of blocks. Only down side is you gotta have a pretty hefty machine to set them. But you could do it in a 1/2 day fairly easy.
 

Futbalfantic

Well-Known Member
Joined
Aug 5, 2006
Location
Charlotte
Call your local concrete plant and see what blocks they pour, as most pour some kind of blocks with the extra concrete. Scm here doesn't do any "architectural" blocks just plain 2'x2'x4' blocks but another company in asheville pours hollow fill blocks that have a rock finish on one side. Either of those options could be done with two layer of blocks. Only down side is you gotta have a pretty hefty machine to set them. But you could do it in a 1/2 day fairly easy.

Do they look nice? Putting in this much work want it to look good.
 

Loganwayne

#BTL
Joined
Feb 15, 2013
Location
Clyde, North Carolina
Do they look nice? Putting in this much work want it to look good.
You'd have to call the concrete plants because some only have the big squares that don't look good, but I can get these below local to me
 

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braxton357

Robot
Joined
Apr 6, 2005
Location
Morganton
You'd have to call the concrete plants because some only have the big squares that don't look good, but I can get these below local to me
American concrete in morganton sells the standard 2x6 3800lb blocks with a faux rock face on one side, I use them a lot and they look pretty good, especially with the capstone they sell too.
Those look even better though and would be a lot easier to transport, hopefully they not outrageous expensive
 

Loganwayne

#BTL
Joined
Feb 15, 2013
Location
Clyde, North Carolina
American concrete in morganton sells the standard 2x6 3800lb blocks with a faux rock face on one side, I use them a lot and they look pretty good, especially with the capstone they sell too.
Those look even better though and would be a lot easier to transport, hopefully they not outrageous expensive
Ya southern concrete does those as well except they don't have the rock face but they are cheap
 

Tom@Hilltop_Machine

Well-Known Member
Joined
Mar 31, 2005
Location
Rural Retreat, VA
I haven't priced them recently but from what I remember they really aren't that bad once you compare them to the structural blocks you can buy that are sold
Okay. I found a place around here that wants 100 bucks a block. Just curious if that was a good price or not. The regular concrete barrier blocks are going for 60 bucks each.
 
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