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We need to build a retaining wall near our pool area. We have not made final decisions on it, but it will be a minimum of 4' tall, and possibly 5' or more.

Many online tutorials recommend solid blocks with a back lip for walls up to 6'. These blocks don't require mortar or additional supports, and the lip makes placement very quick and easy. So I would love to use them.

However, when viewing these products on the websites of the two major home improvement retailers, the official response on all has been that these blocks should not be used for walls in excess of 2'. Said responses have also stated that any wall in excess of 2' tall should be engineered. So I'm unsure if they're saying their blocks cannot be used in a wall taller than 2', or if they're saying that they may work but are unwilling to take liability for that claim due to potentially poor installations.

So can these offset blocks be used to build a 4' - 6' tall wall if the wall is properly designed and constructed? Or would cinderblock with rebar supports be required?


Project Details

In case these details are relevant:

  • This wall will sit just off of our pool area patio, where there is currently a steep slope up to a gentle-sloping side yard
  • The wall will likely be around 15' long, with a max height around 5' at one end and a height of 3' at the other end (the yard being held back is lower over there). There will be stairs at the short end leading up to the side yard
  • I plan to dig 6" down for the first row of blocks, set on paver base
  • I was not planning to pour concrete around the bottom row, but can if necessary.
  • I plan to backfill behind the wall with 3/4" gravel over a 4" drain pipe, all enclosed in landscape fabric, with 3" of topsoil on top. Gravel filled and compacted after each row of blocks.
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    There is another and better choice than solid blocks with lips and cinder blocks with rebar. Look at both Keystone and Versa-Lok (versa-lok.com/products/residential-commercial/standard). These are concrete blocks with heavy fiberglass-epoxy pins which hold the courses together. There may be other similiar systems now. – Jim Stewart Apr 17 '18 at 19:25
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    What sort of guard rails does your jurisdiction require to prevent falls off walls of that height? – Harper Apr 17 '18 at 19:32
  • @JimStewart Thank you for the suggestion. I will look into these. – Nicholas Apr 17 '18 at 19:46
  • @Harper That's a good question; I hadn't considered that. Our county and borough are pretty lenient on these sorts of things but I will double check the codes. – Nicholas Apr 17 '18 at 19:47
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    The big box stores don't have the professional grade product you need for a wall of this type. You need to seek out a precast concrete type company for this type of material, possibly a well established landscape company. The manufacturer of these better products will have all the engineering specifications available. – Paul Logan Apr 17 '18 at 20:34
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There is another and better choice than solid blocks with lips and cinder blocks with rebar. Look at both Keystone and Versa-Lok (versalok.com/products/residential-commercial/standard). These are concrete blocks with heavy fiberglass-epoxy pins which hold the courses together. There are other similar systems now which may be cheaper than Versa-Lok and may be adequate for a wall 4 ft or 5 ft above grade.

Thirty years ago we got a retaining wall built on the downhill side of our lot, wrapping around back until the top of the wall reached grade. The height is 4 blocks or 32" giving a max height above grade of 28".

The contractor used Keystone "compact units" about 44 lb each. The Keystone blocks are held together with stout fiberglass epoxy pegs and have four holes on top for two pegs (and two holes on the underside) giving a choice of two different offsets per course, about 1" and about 2". This was somewhat overkill for this wall, but it certainly has not shifted. I did not want the possibility of blocks on top ever getting loose and falling on a child or a dog.

I think Versa-lok has some features that make installation easier and result in a very strong and long lasting wall which is easier to build. For example Versa-Lok has slits in the top of each block into which a special gripper is inserted to allow carrying and positioning of the blocks with no need to have fingers in danger.

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