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Old 07-07-2011, 01:42 PM   #1
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Need help deciding on cost efficient retaining walls


Hi all,

I'm not sure if this is the best forum to post this in, but I was hoping to get some ideas on cost effective ideas for a couple of retaining walls that I'm looking to help a family member with. I realize that there are many different types depending on the circumstances in which they'll be used, so I'll explain the circumstances below.

First, this property is in upstate NY on a hill where the properties step down according to the slope. The property I'm working on is approximately 5' higher than the adjacent property. One retaining wall will be in the back yard, the other will be in the front along the driveway. I have a PE that I'll be working with on the backwall, although the building inspector says I really don't need one...which surprises me greatly, I always thought anything over 4' needed a PE stamp. But anyway.

Starting with the driveway wall, the driveway slopes from the street down to the house (approx 4' of slope over 30 feet or so). Initially I was thinking of an interlocking block on a bed of compacted crushed stone.....adding fabric every other course or so to tie everything into the wall. Of course backfilling with a foot wide of 3/4 crushed stone and a french drain tied into the existing gutter drains. The building inspector says I don't have to be below the frost line as long as I have good drainage...which once again, surprises me greatly. This wall will slope with the driveway from approx 4' high at the house to one course at the roadway.

I'd then planned on cutting the asphalt driveway to allow the drain to be tied into the corner gutter drains, then adding a two feet wide x 4 or 6" conc slab with a surface drain that ties into the wall drain below (this will be to allow for water that drains down the driveway to the house). I"d planned on covering the new drain in the concrete with some sort of steel grating which can be easily removed to allow for cleaning.

Now, with the backyard. The wall will be approx 40' long by 5' high. I'd planned on using the typical cantilevered retaining wall with a 42-48" wide x 12" high footing....then using cmu block with rebar @ 32" o.c. and grouting those cells solid. Of course I'll be tying the rebar into the rebar into the footing. I'd planned on leaving a brick ledge in the front of the footing to allow for future standard pavers to be stacked in front of the wall for aesthetic reasons. I'll also be backfilling with a foot of crushed stone and adding a proper drain which will be tied into the rear gutter drains.

The sole purpose of this back wall is to level out the backyard and eliminate the sloped area that's there for easy maintenance. The wall will be holding a 5' high by 5' wide triangular area that will be backfilled to level the property.

I hope my explanation of this is enough to get some good advice on what I'm thinking of doing. I realize it can be difficult to visualize the situation from a written description. If anything is unclear, please feel free to ask for clarification as I really want to get this right. I feel it's a fairly big undertaking, and being it's for a family member, I definitely do not want any future problems. I appreciate any insightful advice that anyone can offer and I thank everyone that responds in advance.

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Old 07-07-2011, 02:49 PM   #2
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Need help deciding on cost efficient retaining walls


Since you will be working with an engineer, you really ought to run your situation by him or her. Giving you sound, cost effective design advice is why you hire them after all.

As for building a "typical cantilever retaining wall", I am not sure what you mean. Cantilever walls are usually reinforced concrete, and are normally designed to fit the site, nothing "typical" about them. I would run the idea of building a segmental block retaining wall by the engineer, almost certainly less expensive than a cantilever wall, can by done DIY, and look better in my opinion. Properly designed, a segmental block wall can be over 25 feet tall, more height than you need here.

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Old 07-07-2011, 04:28 PM   #3
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Need help deciding on cost efficient retaining walls


Hi Dan,

Being that the building inspector says I dont necessarily need a PE, I was only going to consult with my friend to discuss what I'm doing....not necessarily hire him to stamp my drawings. I don't have a problem hiring him should it be necessary for the building inspector, but if it's avoidable, I intend on avoiding it. This project is so small in scope, that he really wouldn't be interested in tying up his time to design something so simple due to it costing him too much time from the large scale projects he's typically involved with.

I mentioned the typical cantilevered retaining wall to demonstrate my plan only, not to imply that cantilevered retaining walls are typical for any project. I also have many typical details demonstrating block retaining walls, showing 16" cmu for the bottom courses up to the lower grade and 8" cmu for the remainder of the wall....this allowing for the stacked block or brick facade that I would want to add in the future for aesthetic reasons.

My plan was to use these details (which are for walls up to 10' high), which I know would be more than sufficient for what I'm retaining. In fact, I realize that it's overkill.....hence me inquiring here for additional ideas. And I do agree with you that there are more cost effective ways of doing this which are substantially easier to construct than what I just mentioned.

Personally, I don't feel comfortable using a segmented block wall for the situation in the back unless there's some sort of footing. I just envision sinking blocks into a bed of gravel or lateral shifting due to frost heave. I plan on researching this further to verify what actually holds this wall in place at the base. I guess that's the main question I have, what holds this wall in place from the potential lateral shifting of the entire wall?

When you say segmented retaining wall, I'm assuming that you mean the interlocking blocks that you typically find at larger stores such as lowes or home depot. Please correct me if I'm wrong. Also, please feel free to elaborate on the lack of footing that I seem to be hung up on. I really appreciate any insight you have.
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Old 07-07-2011, 04:42 PM   #4
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Need help deciding on cost efficient retaining walls


Segmental block retaining walls use cmu (concrete masonry units), stacked together. When the wall gets higher than about four feet, the wall also needs soil reinforcing, which is often provided by cloth, sometimes by metal wire mesh, and sometimes by metal or plastic straps. The exact technique is normally specified by the manufacturer.

Segmental block walls typically require only a gravel or crushed stone footing, you don't need a concrete footing, you just need reasonably strong soil, no organics, no soft clay, no loose silt. The manufacturer of the blocks will generally provide a footing detail for their particular block. The blocks do not shift because the blocks actually do very little work, the soil behind the blocks provides the majority of the support, which is totally different than a cantilever retaining wall, where the concrete in the wall provides the majority of support for the wall.

When the wall is four feet or taller (each manufacturer has a different cutoff), the soil is reinforced as I noted above, which again allows the blocks to do little work. This type of wall is easy to build, flexible, strong, and cost effective. Frost heave is not an issue unless you have soil which is highly prone to frost heave, which generally means you have fine sand or silt, in which case you should consult with the manufacturer of the blocks for recommendations on the footing required. This type of wall, like other walls, normally requires drainage on the uphill side of the wall. See manufacturer's recommendations for the method of draining.

The wall also requires select granular backfill (structural fill) on the uphill side. The manufacturer will specify the mix, which generally contains gravel or crushed stone, sand, and a controlled amount of silt. The manufacturer will show in their details how much structural fill is required.

I built a wall like this in my backyard, very simple project. Many others on this site have built more complex walls. Most all would likely agree that the hardest part is the excavation, actually placing the blocks is easy.
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Old 07-07-2011, 07:13 PM   #5
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Need help deciding on cost efficient retaining walls


I've done some research now, although it's limited, so I don't feel I have all of the answers.....but I'm definitely moving along. I appreciate your thoughts Dan, it is helping me. I just find it difficult to believe that they don't use anything other than compacted stone for a footing.

I do agree that the wall isn't doing the majority of the work of holding back the earth, I understand the concept. I also understand about the fabric tying into the earth behind the wall. I just have a hard time understanding what prevents the wall from shifting forward at the base where it meets the earth.

I can see it holding well if the wall is buried a couple of feet below the low grade side...using the earth on the low side to resist lateral movement at the base. I'm assuming that's ultimately what holds the base of the wall in place, am I correct in my assumption.

Water is somewhat an issue here, although I'm not sure how much. This wall is being built for two reasons. First and foremost, to alleviate my relative from having to maintain a sloped hillside as she gets older. Second, she just bought the house about six months ago and she has a problem neighbor on the next lower property complaining of the water runoff that seeps onto her property.

I know for a fact that this will not solve that problem because there are two other properties that are adjacent to the neighbor with the problem. They're both higher than my relatives property, and both appear to be draining into the problem neighbors property. So this is also to alleviate blaming my relatives property from the cause, and shift the blame where it should be....to the other two properties. In my opinion, my relative is too nice, I wouldn't be doing anything to solve problems in a house I just bought when I haven't done a thing to the property to alter it....but that's just me.

So yes, water is somewhat of an issue, so I plan on adding the 3/4 crushed stone behind the wall (1 foot wide), and adding an appropriate drain to tie into the existing gutter drains. I also plan on wrapping the stone with fabric as I'm backfilling to eliminate clogging the stone with fine material. Do you feel this is a good idea?

Lastly, what block did you use for your project? I realize that there's a myriad of choices out there, now it's a matter of cost effectiveness. I did a quick price check of the versa lock blocks, and wow, talk about sticker shock. They were over six bucks a piece, which amounts to 750 bucks for each foot in height of the 40 foot wall. Bury that two feet, which would make the wall 7' high in total, and now you're talking roughly 5500 bucks for the back wall alone. Figure in another 500 for the crushed stone, and now we're talking 6k in materials for a wall that will never be seen. Can you think of a better choice than the versa lock?
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Old 07-07-2011, 07:16 PM   #6
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Need help deciding on cost efficient retaining walls


oh, and one last thing....I've always known cmu block to be "cinder blocks"....with the two hollow cells in the middle. Are you referring to the interlocking blocks when you say cmu blocks?
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Old 07-07-2011, 08:45 PM   #7
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The term cinder block refers to blocks literally made from wood cinders. Cinder blocks have not been manufactured for probably a hundred years. Blocks now are almost entirely concrete, hence the term cmu (concrete masonry unit). Generally the blocks used for retaining walls are solid. The blocks with holes are used for foundations, and are sometimes used for walls, but they are not used for segmental block retaining walls.

The important detail in the block is the presence of a key on each block. The male key fits into the female groove, causing each layer of block to offset back the correct amount, thereby making you build a slightly battered wall. So called cinder blocks (actually concrete block) do not have a key, and are not generally suitable for reinforced earth walls.

We built our wall with Ideal block, which is manufactured locally. We purchased a total of approximately 200 blocks, each block 6 inches high, 8 inches wide, and 12 inches deep, with a textured face that looks like stone. We also got some flat blocks for the steps, and some special blocks for the corners, but effectively it was $1000 for 200 blocks, or about $5 each. This is not much different than the quote for Versalok that you got.

Now to the question of what prevents the wall from sliding. This may be hard to wrap your arms around, but if you look at the mechanics of the wall, the soil behind the wall exerts virtually no lateral pressure on the block, assuming you build the wall according to manufacturer's directions. The soil supports itself. When the soil gets above a critical height, you need to install the reinforcing, but if you do it according to recommendations, the reinforcing supports the soil. Reinforced earth walls would hold themselves up without the block, however the block is there to prevent erosion of the soil, and to present an attractive appearance to the wall. Unreinforced earth walls (typically less than four feet tall) require some contribution from the block to hold themselves up. But in no case do you need to, or even want to, bury the block, install a concrete footing, or in any way deviate from the manufacturer's recommendation.

I installed my block directly on glacial till, no footing at all. No problem. The wall is only three feet tall, so it was pretty easy. I backfilled approximately one foot behind the wall with crushed stone (I used the same crushed stone for mixing concrete for my deck footers). No drain required in my case. Segmental block walls less than four feet high may not need a drain, see manufacturer's recommendations, because water will flow through the face of the block.
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Old 07-08-2011, 11:25 AM   #8
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Need help deciding on cost efficient retaining walls


Yeah, I knew that about "cinder blocks", but I've always known cmu to be the same style...the 7 5/8" blocks with the open two cells in each. I've never heard of interlocking blocks referred to as cmu block. That's just my experience.

The sections and installation guides I've seen all seem to show at least the bottom course shown below the low side grade, but definitely not below the frost line by any means.

I'm definitely going to put a drain in that ties into the existing gutter drains, no if's ands or buts about that one. If the neighbor were to see water seeping from the wall in any way, a complaining she will be. From what I know, she's seeking legal action to address this issue with the so called water in her back yard. Personally, I don't see how new owner can be held liable for water problems that have been there for years when the new owner hasn't done a thing to change the property in any way. So this is also meant to quiet the neighbor and eliminate my relative from having to listen to this neighbor complain and shift the blame elsewhere.

At this point, it seems to be a matter of researching the myriad of choices, and I'm now contemplating doing a stepped tier system which would allow for a raised planter between the two walls. This would allow me to decrease the cost of the blocks used substantially. This would also allow both walls to be under three feet high, which would open up more choices.

Please correct me if I'm wrong, but the research I've done seems to show that the horizontal surface of the planter should be at least twice the height of the lowest/front side wall. I hope that explanation is clear enough.

Forgive me for all of the questions, but my relative is somewhat indecisive at this point as to what she actually wants, so I'm exploring as many options as possible to get the best price, and not get myself into a project that's over my head.
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Old 07-08-2011, 12:14 PM   #9
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Need help deciding on cost efficient retaining walls


If you want to some research, go to the sites of any one of the 4 major retaining wall licensors (Allan Block, anchor Wall Systems, Keytstone and Versalok), that may also make to block near their headquarters. They also license producers in the U.S. and world-wide.

The web sites all have very good technical and construction details. These units all have many different size and shape units, but from a use all have generally the same basic information since they are frequently used in state, county and municipal department for their use and information. The common installation methods have been developed by their engineers working with geologists, deign and construction engineers, and DOTs for about 20 years.

Beware of some of the similar "knock-offf" local units that do not have the same features for legal reasons.

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Old 07-08-2011, 02:37 PM   #10
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Originally Posted by concretemasonry View Post
If you want to some research, go to the sites of any one of the 4 major retaining wall licensors (Allan Block, anchor Wall Systems, Keytstone and Versalok), that may also make to block near their headquarters. They also license producers in the U.S. and world-wide.

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I've been doing so much research about this and I hadn't thought to do that. Keystone has some really cool ready made plans that have given me great ideas. I also found a local distributor.
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Old 07-08-2011, 03:12 PM   #11
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Need help deciding on cost efficient retaining walls


I had been to allen blocks and versaloks websites, but I haven't heard of keystone or anchor wall systems. I'll be researching them as well, so thank you for the advice.
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Old 07-08-2011, 04:50 PM   #12
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Need help deciding on cost efficient retaining walls


You will find the same basics for installtion because the product has been researched for so long after being copied from elsewhere using different manufacturing techniques. The 4 major systems have been used globally because of the cost and ability to build strainght or curved walls (inside and outside curves) of gradually varying heights.

I have seen walls about 7 miles long built that were between 4' and 40' high without concrete footings but they were engineered because of the heights and geometry to follow a freeway.

For a DIYer, any of those a piece of cake if you get a excavating contractor and are willing to work or have the stacking hired out.

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Old 07-09-2011, 10:15 AM   #13
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Need help deciding on cost efficient retaining walls


Once again, thanks for the advice....but I'll be doing this myself, and I feel confident that I can do the design and the build properly. I generally do my own construction when it comes to my families' or my own property, and although I'm not able to do it with the speed and efficiency that a professional would, I feel that I can certainly do a solid job that will stand the test of time. I've been fortunate in that the things I've built have not had any issues....but I'm forced to spend alot of time in research that a professional would normally get from the master teaching the apprentice face to face.

I guess that's the good thing about being a designer...when you plan it all out, every piece, then you can generally have a good handle on getting the layout correct. And as I've read, the key to this project is getting the base and first course as true as possible, from there it's fairly straightforward. Please correct me if I'm wrong, and offer any instructive tips that can help me in any way. I'm certainly not claiming to be a pro here and I can use all the help I can get.

Unfortunately, I have to dig this all by hand due to the severe space limitations and the neighbors fence being very close to the area that I'll be working in. On the fortunate side, the slope that I'm eventually going to flatten and retain doesn't have to be dug a tremendous amount. I'm sure the lovely fill and rock of upstate ny will not be friendly, but unfortunately this is how it has to be.

I could also use some tips or links to how to build the stairs properly. This fence is ultimately going to be a "L" shape with a radiused corner....with stairs protruding through the radiused section. I guess I'm unclear on how to ensure that you get solid drainage under the stairs.

I also have to research how to properly allow the drain to pass through the wall to tie into the corner of the house gutter drain.

I'm sure there are plenty of details on the websites, and I'll definitely research these there. But sometimes the means and methods of the pros can offer practical advice on the actual how-to of the project. So once again, please feel free to chime in on these questions I have. I'm more than willing to learn as much as possible.

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