Hiring contractor to build 3' retaining wall

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Old 09-24-11, 11:06 AM
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Hiring contractor to build 3' retaining wall

A previous owner built a small cinder block retaining wall, perhaps 50 years ago, between my property and the driveway next door. About 32' feet long, it is now two different heights and is cracked and leaning. I got estimates to tear it down and rebuild a new cinder block wall.

It appears that it can be built to be only 3' tall, plus a 12" footing, which is the limit before having to get a permit from the city of Los Angeles.

Two contractors ended up bidding against each other, going lower and lower. One is not the person on the license, but I called the license owner and he OKed it. The license owner told me things to look out for in building the wall. For instance, all holes must be filled with cement from top to bottom. He said some contractors make it appear that they've done this when they haven't and the wall is not strong.

In the last round of bidding, I asked if all the holes would be filled top to bottom with concrete. The man associated with that contractor said at the current low price he could not afford to do that and neither could the other contractor. He then said that would be as expensive as building a concrete wall, which is a better wall.

He gave me a price on a concrete wall--raising the price after I asked how he's going to deal with water runoff so it won't upset the neighbor. I think both men were going to space the cinder blocks at the bottom so the water would weep out, but for the concrete wall he was going to run a pipe to the front of my property and the water would empty onto the sidewalk.

He also said that he uses materials superior to those used by most contractors, including 2500 psi concrete, while most use 2000 psi, and US rebar as opposed to Chinese.

I would like to know what is really important for building a good wall of this size.

Is the difference between cinder block and concrete significant?

Are the differences between the concrete and rebar types he mentioned significant?

Should 100% of the holes in the cinder block be filled top to bottom, or is there a minimum that is sufficient?

What about placement of rebar vertically and horizontally?

Should there be sand, gravel or a waterproof material below the dirt next to the wall?

If the wall ends up over 3' in any spot, can the city make me tear it down or do anything else?

What else do I need to know, and how can I tell if the contractor is doing what he says he's doing, other than paying more for an inspector to watch the process? I would like to go to the store with the person I hire and pay for the materials directly.
 
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Old 09-24-11, 06:37 PM
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My parents had a retaining wall in the front of the house. It held the dirt from falling on the sidewalk. It started to lean & they had someone remove it. Instead of building another wall, they sloped the property so only one row of block was needed. Is there any way that you could do that?
 
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Old 09-25-11, 06:32 AM
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Even though there is a difference between cinder block and concrete block, you won't find cinder block anymore.

I have a similar problem that you do. Concrete block retaining walls that are falling over. Everywhere I go and see this type, they are leaning. In my research to replace them, I found the concrete block walls are not the way to go. To have them perform properly to resist falling over, you need to use a lot of concrete and have a very large concrete footing. The footing needs to extend to one side 2/3 the height of the wall. You also need rebar in the footing that extends up through the holes in the block that also need to be filled. I recommend using segmented concrete blocks for your new wall. You don't need a concrete footing for them and they remain flexible enough to tolerate ground movement without falling over.
 
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Old 09-25-11, 12:57 PM
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Originally Posted by drooplug View Post
I recommend using segmented concrete blocks for your new wall. You don't need a concrete footing for them and they remain flexible enough to tolerate ground movement without falling over.
They also stack in a negative attitude toward the dirt emphasizing it's own holding ability.
 
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Old 09-26-11, 10:28 AM
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I think this is the fifth time I've tried to reply here. I keep getting cut off.

I called Building and Safety to ask if segmental blocks are OK for a 3' wall and the man I talked to said he didn't know anything about them. But a 12" footing is required and there are specific rules for rebar and mortar mix, so I don't think they would qualify. The man called my wall a slough wall rather than an actual retaining wall.

I'll talk to a company in the area that sells these blocks and see what they say.

I also considered sloping the ground to avoid walls completely, but some contractors said that would put my foundation at risk, since I only have a crawl space and the wall is about 10' from the house, so the sloping would have to start right next to it. Others were not worried, but I don't want to risk it.
 
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Old 09-26-11, 03:14 PM
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I don't believe that the slope would create any danger to the foundation. The slope would be in the right direction.
 
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Old 09-26-11, 03:53 PM
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Sondra -

You talked to an idiot that is not informed. Usually Building and Safety has knowledgeable people. In many areas, states, counties and municipalities have standard design plates for their crews, contractors and home owners.

In your area, the maximum height for an unreinforced (no grout) segmental wall wall is 3' (probably because of the seismic), but it is usually 4' or 5' in other areas.

To get an idea of the concept, go to one of the sites of the 4 major product lines (Allan Block, Anchor Wall Systems, Keystone and VersaLok) that all have good design (size, shape, configuration, texture and colors) and installation instructions and design guides that apply in most states and countries.

There are a number of suppliers of the different units in California. Some of the major ones are Orco Block, Angeles Block, RCP and Basalt in the north. Most sell small jobs only through distributors/dealers. I found the 3' limit by looking at one of the producer sites, since they had local requirements.

Your use is a casual or landscaping one, but the systems are not "fly-by-night" and are made in many countries and used up to 30'-40' high with no concrete footings allowed and no steel reinforcement, mortar or grout, but these must be engineered.

In your case, you may have to get rid of the existing concrete footings.

Dick
 
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Old 09-28-11, 02:50 PM
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For a 3' high retaining wall concrete is easily the best way to go and it's usually NOT the most expensive. As for specs on a concrete wall: 8" thick wall, 4 #4 rebar (2 4-6 inches above the bottom of the wall and 2 about 6-8 inches below the top) running continuously from end to end, a 12 x 8 inch footing with 2 #4 rebar running through it and rebar at 18" intervals extending out of the footing and into the concrete wall and it's been 25+ years since I've poured any concrete that wasn't at least 3000psi. Most concrete retaining walls have weep holes near the bottom of the wall spaced every 5-10ft to allow for drainage from the back of the wall to the front. However if you have a problem with water getting on your neighbor's property then run a perferated drain pipe along the back of the wall from end to end with one end exposed for drainage. Surround and bury the pipe in gravel (about a foot) as you go before backfilling the wall. And depending up your overall length of wall you might want to consider adding a few deadmen as anchors. OR you can go with Pavestones, Anchor wall systems, etc. Usually more expensive material wise, but the labor isn't bad and it is something many people can do themselves. Good luck.
 
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Old 10-01-11, 09:14 PM
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Thanks for the suggestions. I just saw a new contractor and he immediately wanted to go with concrete blocks. He also wants to pull a permit, even if the wall is 3 feet high. (As for the segmental blocks, I've decided to opt for conforming to code rather than going for beauty or even a possibly stronger wall.)

I pointed out to this contractor that I have sprinklers very close to the wall--about 2 inches. He said they wouldn't have to be moved. When I talked to him again, I asked if putting in gravel next to the fence would interfere with the sprinklers and he said it wouldn't. Other contractors had said the sprinklers would have to be taken out and replaced later. Is this guy right?
 
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Old 10-02-11, 06:48 AM
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It all depends how much room there is to dig around the poly pipe. If you hit a line while you're digging, you just splice it back together when you back fill. It's not a big deal either way. How many sprinkler heads are near the wall?
 
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Old 10-02-11, 06:10 PM
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I'd never counted. It turns out there are three. So I won't worry about that.
 
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Old 10-03-11, 03:14 PM
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Why, oh why, since you are planning to have this work done by a contractor anyway, do you not spend the $250 to $300 (that's a typical price for around here) and have a professional engineer produce a drawing? That gives the contractors exactly the same project to bid which makes your job easier to decide which one knows what he's talking about, it puts the liability for any design problems with the engineer, and if the winning bidder fails to build per drawings you have complete recourse to go after them for rework or a refund because you remove any excuse for doing the work incorrectly.
 
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Old 10-05-11, 01:52 AM
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A few thoughts (I'm a P.E., but not licensed in CA):

Hiring an engineer for a 3' wall is like using a howitzer to kill a mosquito--will definitely work, but considerable overkill. And in CA, I suspect you'll wind up paying more like $500 or $600 for his/her time and a sketch.

Why not do the sketch yourself, for all bidders to use? I've designed and poured several 3' retaining walls in the last 30 years (none failed yet, as far as I know), and usually did walls 6" thick, with No. 4 (L-shaped) bars at 2' centers vertically into the footing, and a single mat of No. 4 continuous longitudinals 10" or so apart. Footing size 6" thick by 18" wide, placed on compacted, well-drained base (compacted gravel, at least 4" thick). Don't go less than 3000 psi concrete, and plan on moving the sprinklers, as 2" setback won't leave enough room for the wall forms or footing. Include wording in the contract that any damage to existing irrigation features or landscaping/sidewalk/driveway features will be repaired by the contractor at his cost.
 
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Old 10-05-11, 07:09 AM
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What's wrong with hiring someone? Maybe we wouldn't do it but it's okay in my book. Actually, I would hire 2 day workers.
 
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