Demolish and replace an exterior retaining wall

23 Replies

Hello BP,

Does anyone have any experience demolishing and rebuilding landscape retaining walls? I have a wall that needs to be taken down and rebuilt (or graded) and I'm wondering what my options are in terms of putting up another wall or just grating the soil as a slope after the concrete wall is removed. This wall is right next to the driveway, where an old "shed/garage" used to be. I'm also not sure what the cost is to do this, I'm working on getting a few quotes, unless I can handle the demo myself. Any thoughts?

Wow, I would really not want to mess with that one. Get a good excavation contractor to take a look at that one. That could be really, really dangerous if you don't know what you are doing.

Hi Justin,

Depending on where the property is, the rules are different.  In California where I'm at, because of earthquakes, retaining walls that are on a steep grade, have structures within a certain distance, higher than 36" (or 42 maybe, can't remember) all require a permit.   

Some counties have permits for demo, some don't.   If it were me, I'd look into that stuff, get a couple contractors or engineers out to look at the retained earth and then decide.  If it were just holding back some yard, with no structures relying on that soil, I'd rip it down myself with a jack hammer and sledge hammer.  

From the looks, seems you're in the 4-5' high range?  That's a pretty decent grading job to slope it so it doesn't keep collapsing on you.

Allen

@Allen Maris  Great point, I didn't think about this potentially requiring a permit...I'll look into that for sure. And yeah I think I'll need an expert's advice to determine whether to grade or rebuild.

@Peter Jordan  I've decided that I'm going to have an excavation contractor take care of this. There's too many variables of safety for me to consider it.

Thank you both for your input!

-Justin

yes, i used to do landscape and this is a big job. expect to pay at least 5k. a very experienced contractor has to get it done. i'd even budget for 10k, personally.

@Justin I've acquired a similar retaining wall challenge.  They are very simple to build.  I think it's very difficult to fix, but I've not tried to fix .. always rebuild.

To build, you demo never standing in front of the wall.  Then dig to a footer level.  The footer should be WIDE.  Remove a lot of dirt so you won't put pressure back on the wall.  Backfill with good piping and drainage stone and a shallow layer of dirt on top.  

Depending on the $ of the neighborhood, you can go with cinder block, cross ties, landscape timbers, Home Depot wall system, etc.

The wall I have is straight up like yours.  I'm planning on terracing the new wall.  Instead of 5' wall.  It will be 3', then a garden bed, 2 ft wall.  Much less technical to build.  Adds more curb appeal than a shear wall.  

I'd rent or hire an excavator to clear things out, but building the wall is very simple.  Just laborious.

@Justin J.  Best of luck.  What's the new wall going to look like?

Cheapest solution might be to leave it in place and fill the downhill side with soil sloped at 3:1 (that is 5 ft tall wall would extend 15 feet from the toe of the wall if the catch slope is flat). That only works if you have the space and cheap fill material.

If you are tiering it like @Rick Baggenstoss  suggested, then you could also leave the existing wall in place and start a few feet away.

It looks like it maybe set on or near the property line so be careful not to trespass with your solution.

@George P.   Wowsers 5-10k! I didn't think it could go out that pricey for what initially seems like a small job. I'll be sure to plan for more than I expect, thanks for your input George.

@Rick Baggenstoss  I would think rebuilding might be a better long term solution for the wall. I'm afraid that if I tried a fix, a big storm might erode whatever fix that I may try. Excellent suggestion with the terracing, I didn't think of that! It's more on the middle to low class/college students type neighborhood. I'm not familiar with the types of wall materials but I assume cinder blocks and wood based features are the lower end, might concrete last longer? I like the idea of building in a terrace to add a garden of some sort, I might consider that. 

Originally I was thinking that the wall would look similar -strong, simple and cost effective but you've expanded my creativity on the possibilities.

@Bill S.  Good suggestion Bill. This wall is adjacent to a detached garage that was demolished, so this space would ideally be used as additional parking. I need to retain the space up to the wall, so grading it over the wall probably won't work for this application. Property lines ahh! I'll be careful not to disturb the neighbors; If a contractor messes up and removes too much soil which damages or collapses a neighbors wall uphill am I responsible for re-mediating it or will the contractors insurance cover it?

@Justin J.  If I was the neighbor I would probably sue both of you and let the insurance companies figure it out.

Does the picture show what you are thinking? Again easiest to leave the existing wall in place and just cover it up.

Can't get the picture to work.

@Justin J.  

Is this wall solely on your property or does it divide your lot from a neighbor? If the wall is only on your property you could totally DIY the project. If not, you will probably need a pro. If the wall represents the dividing line between you and a neighbor, are you on the uphill or downhill side of the wall?

If it can be determined that the wall was built by the neighboring property, and now it encroaches on your side, you may have a good case to get them to repair or replace the wall. Either way, it may require an engineer to assess the current danger and necessary remediation. 

Keep us all posted on what you do!

@Bill S.  I will be getting a better picture of the wall in the next two weeks, and i'll give some insight on what I'm thinking for the fix when I post them here.

@Douglas Larson  This wall is solely on my property, the property line is about 7 feet away from the wall separated by a few tons of soil. I'm bringing in an excavation contractor and an engineer to assess safety as well as the plan moving forward. I'll post here when I know what I'll be doing moving ahead. Ideally this will be a DIY project.

-Justin

@Justin J.  good plan let us know how things turn out.

Typically, a retaining wall will have dead men, or anchors, 15' or so behind the wall (buried in the earth) connected to wall by rods.  This of course requires additional excavation.  A free standing cantilever wall will not generally take the load.

@Wayne Brooks  Would a design such as this be a sufficient way to approach the plan? 15' back may be overkill for the wall. I was thinking that a base slab footing like this could work for holding the weight.

-Justin

Not an engineer by any means, but I would be suspect of a cantilever wall, like above, but if that's what you build....You most certainly do Not want a construction joint as shown, you want one continuous pour for the wall.  You also will need rebar in the footer, And protruding up from inside the footer (prior to pouring the footer) into where the wall will be poured.  Then you'd have additional rebar tied on to the rebar protruding from the footer, up the height of the wall.  I assume the footer and wall would be poured at separate times.

@Justin J.  as @Wayne Brooks  said you must have steel in your footer and wall. The wall and footer must be completely ridged as a unit. What keeps the wall from doing what your existing wall did is the weight of soil above the footer behind the wall. You also want a keyway into the soil under the footer to keep the whole wall from sliding. Not sure why you would have a joint half way up the wall. The wall should be formed and poured all at once.

There are several types of retaining walls.

1) A gravity wall is a huge mass of concrete that uses the weight of the concrete to prevent the wall from overturning. These are shaped like a fat giant wedge with the wide side down. No footer or reinforcement needed. It takes lots of concrete but is less technically challenging to design.

2) A reinforced wall (the one in your sketch) use the weight of the soil above the slab behind the wall to prevent the wall from overturning. The wall and footer are tied together with reinforcing steel which keeps the wall from rotating about the connection to the footer. This involves the complicated design of a concrete structure as well as the wall to hold the soil.

3) The deadman wall mentioned by Wayne which uses the resistance of the deadman behind the wall to prevent the wall from overturning. There must be an adequate number, space, and length of the deadmen to keep the wall in place.

4) The geotextile wall is a variation of the deadman wall. It's easier to design, cheaper to build, fairly durable. Unlike the other walls, the actual face of the wall carries very little load. It is widely used in this area.

Here any wall over 3 ft tall requires a professional engineer to design and stamp the plans. You should have a geotechnical report that describes the properties of the soil that the engineer would use in their design.

Unless you have some real experience with wall design I would say you have more than a 90% chance that your wall will fail just like the one did that is already there.

Justin, it sounds you are doomed.  ^

Seriously, like 90% doomed.

If I lived next to you, I'd be checking my prepper stash.  This is gonna get real.  

Well, you're not going to want to build this wall in poured concrete. But, assuming you're acquainted with a shovel and a level, take some of Rick B's advice and look into the manufactured blocks that are made specifically for what you are doing. Watch some of the block manufacturer's videos.  Do some study.  Read.  Enjoy.

The worst part of this job will be demo and hauling the old material away. By counting the existing 8" tall CMU's in your photo, this wall looks closer to 6 feet tall to me. That's a lot of concrete and rebar... do yourself a favor and get some bids on the demo/hauling.

Yes, you'll need a permit, and yes, you should call the building department and ask about height limitations, engineer stamp requirements, property lines, setbacks, skirt lengths, and giant schnauzers.

But maybe before you alert the townfolk of an imminent geotechnical disaster -- a couple deep breaths and a coffee might be in order. You're not building a spaceship -- it's essentially a big pile of dirt.  Pretty sure you can do this. 

Justin,

Are you going to have cars parked above the wall? How tall and long is the wall? Is there any cracking within the wall or is it just starting to fail (tilt) as one piece? What do the soils look like behind the wall?  These are just a few questions I would ask to get started. If your answer to my first question is "yes" then I would strongly advise you to not make this a weekend DIY project. 

Make sure to get any necessary permits, it is important to keep the city after your back.

Justin, just now reading this thread.  Did you end up fixing the wall? What were the final details? 

I would add a french drain to the bottom of the wall for drainage. Allow this to daylight out at grade or just above.  I would have a couple inches of rock against the entire height of the wall to relieve any hydrostatic pressure. 

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