--- title: Structural Retaining Wall Design description: A Structural RW Design is an onsite consultation to look at a wide variety of factors that influence the design and construction of your wall. image: https://back40landscaping.ca/hubfs/Imported_Blog_Media/120240704_164845-scaled.jpg --- 3 Min Read # Structural Retaining Wall Design Oct. 04, 2024 A Structural RW Design is an onsite consultation to look at a wide variety of factors that influence the design and construction of your Allan Block retaining wall. This design takes into account the layout and desired use of your yard, municipal building bylaws, Allan Block installation requirements, and equipment access.![](https://back40landscaping.ca/hs-fs/hubfs/Imported_Blog_Media/2AB-Slope-below-wall.jpg?width=960&height=582&name=2AB-Slope-below-wall.jpg) **Here are a few examples that a trained & certified Allan block installer would take into account when creating a Structural Retaining Wall Design.** ### Slope Below/Above Wall Slopes below the wall will require additional block to be buried in the ground. The Allan Block spec for how much block to bury is enough to create a level space of 5-7’ in front of the wall. Slopes above the wall create weight surcharges and RW reinforcement must be built into the wall. Failure to do this will cause the wall to lean forward and fall in time. ![](https://back40landscaping.ca/hs-fs/hubfs/Imported_Blog_Media/320231019_094920-1024x461.jpg?width=960&height=432&name=320231019_094920-1024x461.jpg) ### Weight Surcharge On Top of Wall: Vehicle, Pool/Hot Tub, Buildings, Etc. Typical RW design is based off of flat land on top of the wall. Adding additional weight is not a problem as long as the wall is built to handle this. An Allan Block RW can be reinforced to handle vehicles, pools/hot tubs, buildings, and more! ### Trees Above/Below Wall Trees in the vicinity of any concrete structure can be a problem. Allan Block RW can handle the roots the best as they can flex instead of cracking. However, care should be taken to ensure the roots, and canopy of a tree are as far away as possible. In general, the canopy of a tree should stay a minimum of 3’ away from the RW. ![](https://back40landscaping.ca/hs-fs/hubfs/Imported_Blog_Media/420220716_100429-1024x577.jpg?width=960&height=540&name=420220716_100429-1024x577.jpg) ### Water/Drainage Management Water adds a significant amount of weight a RW has to retain. Limiting this weight by draining the water away is the most overlooked part of a Structural Retaining Wall Design. Gravel is used to move the water to a pipe that carries the water to a desired location. Pipe is not always required, but this decision should be made by a trained certified installer. ### Curved Walls Stronger Than Straight Not to say straight walls are weak, but curved walls are stronger. Curves can be used for additional strength, or design elements. Curved walls really elevate the look of a retaining wall, and create a focal point. Important to note curved wall install in the same amount of time, however cutting the caps to finish the wall does take longer than simply placing straight caps on the wall. ![](https://back40landscaping.ca/hs-fs/hubfs/Imported_Blog_Media/520240325_114015-1024x577.jpg?width=960&height=540&name=520240325_114015-1024x577.jpg) ### Stairs Stairs are easily built into retaining walls, but they do take a considerable amount of time, and material to build properly. A 4’ wide staircase requires a minimum excavation of 8.5’ wide. This accounts for 12” of gravel and 12” of block on each side of the staircase. As the staircase goes up the sides of the stairs get wider. The amount of soil excavated, gravel and blocks used adds a significant amount [time and material costs to any project](https://back40landscaping.ca/education-center/retaining-wall-cost-fraser-valley). Stairs cheaply built will sink, and become a tripping hazard, whereas high quality stairs add value and function. ### Block & Cap Options: Colors, Sizes, Uses Blocks and caps come in a variety of colors and sizes. Grey concrete is the cheapest color, while Silverado or charcoal are the richest looking color. Contractors should be using the 18” wide block not the 9” block. Caps can be 12 or 18” wide. The 12” cap curves nicer, the 18” installs faster and looks best on straight walls. There are 2 styles of 18” cap. One works slightly better on straight walls than curved walls. Corner units come in 12 and 16”. Often times they are used incorrectly. 12” units should only be used as a step down, and the 16” should be used for 90° corners. Step downs in general have a few options, and what works best should be decided by a trained and certified installer. ### Excavation Excavation is the process of making room for the block and gravel below and behind the retaining wall. Due to how much soil should be removed, and how much gravel should be used doing this by hand is not practical. Compact equipment moves this soil to the road, and then brings in gravel to replace it. The excavation should be at least 10” deep, 30” wide, and as long as the retaining wall. This allows room for the block to be installed and a good drainage zone of gravel behind the wall. ![](https://back40landscaping.ca/hs-fs/hubfs/Imported_Blog_Media/620230323_125540-1024x768.jpg?width=960&height=720&name=620230323_125540-1024x768.jpg) ### Base Gravel Material The base gravel is what supports the retaining wall, and is the foundation to a long last RW that doesn’t sink or settle in time. Look around and you will notice most RW settling in places. Sand and fine gravels are tempting to use as they level really easily. The problem with this is over time this material moves and washes away. Using a coarse gravel is much harder to use, and level, but it will last a lifetime, and never erode. Knowing and using the best gravel for your retaining wall is more important than choosing a gravel that is easy to work with. ### Backfill Soils/Compaction Retaining walls backfilled with loose material have a lot more weight and pressure added to them. Reusing the onsite soil instead of drainage gravel will shorten the life of your retaining wall, and is not correct. Instead, compacted drainage gravel should be used behind the wall. Once gravel is placed in and behind the blocks, a compactor must be run directly on top of the blocks to compact the wall and gravel. This is oftentimes an overlooked step that is not known by contractors.   The Allan Block Technical Installation Manual (code book) goes into a lot more detail than I’m presenting here. This is meant as a quick read to make you aware of the most common Structural retaining wall designs that we take into account when conducting our site consultation and retaining wall inspections. Tags: [Quick Reads](https://back40landscaping.ca/education-center/tag/quick-reads) | [Retaining Walls](https://back40landscaping.ca/education-center/tag/retaining-walls) ![back 40 landscaping retaining cost guide in abbotsford, bc (1)](https://back40landscaping.ca/hs-fs/hubfs/Foundation%20Images/back%2040%20landscaping%20retaining%20cost%20guide%20in%20abbotsford%2c%20bc%20(1).png?width=400&height=400&name=back%2040%20landscaping%20retaining%20cost%20guide%20in%20abbotsford%2c%20bc%20(1).png) ## Planning Your Project? Get the Cost Insights You Need - Accurate price ranges for popular landscaping services - Tips to help you budget effectively and avoid surprises - Features and materials for your project [Access Your Cost Guide double_arrow ](https://back40landscaping.ca/landscaping-retaining-wall-cost-guide) ## Related Articles [![](https://back40landscaping.ca/hs-fs/hubfs/Imported_Blog_Media/amazing-backyard-find-2021-08-29-04-20-25-utc.jpg?width=352&name=amazing-backyard-find-2021-08-29-04-20-25-utc.jpg) ](https://back40landscaping.ca/education-center/landscape-design) ### [Landscape Design](https://back40landscaping.ca/education-center/landscape-design) [Quick Reads](https://back40landscaping.ca/education-center/tag/quick-reads) | [Retaining Walls](https://back40landscaping.ca/education-center/tag/retaining-walls) Landscape design can change any new landscape, or old outdoor living space to make it more practical or aesthetic for homeowners. Landscape design incorporates hardscape... 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[![](https://back40landscaping.ca/hs-fs/hubfs/Imported_Blog_Media/paver-fireplace-lakeview--1.png?width=352&name=paver-fireplace-lakeview--1.png) ](https://back40landscaping.ca/education-center/how-to-improve-your-outdoor-living-space) ### [How To Improve Your Outdoor Living Space](https://back40landscaping.ca/education-center/how-to-improve-your-outdoor-living-space) [Quick Reads](https://back40landscaping.ca/education-center/tag/quick-reads) | [Retaining Walls](https://back40landscaping.ca/education-center/tag/retaining-walls) The summer is a time for grilling, drinks with friends, and outdoor celebrations. Readying the patio is on the top of our list of things to do when the weather starts to... ```json { "@context" : "https://schema.org", "@type" : "BlogPosting", "author" : { "@type" : "Person", "name" : "Natasha Maerz", "url" : "https://back40landscaping.ca/education-center/author/natasha" }, "dateModified" : "2025-03-04T21:52:44.564Z", "datePublished" : "2024-10-04T23:29:03.000Z", "headline" : "Structural Retaining Wall Design", "image" : [ "https://back40landscaping.ca/hubfs/Imported_Blog_Media/120240704_164845-scaled.jpg" ], "mainEntityOfPage" : { "@id" : "https://back40landscaping.ca/education-center/structural-retaining-wall-design", "@type" : "WebPage" }, "publisher" : { "@type" : "Organization", "logo" : { "@type" : "ImageObject", "url" : "https://back40landscaping.ca/hubfs/Imported_Blog_Media/back-40-landscaping-logo-transparent-3.png" }, "name" : "Back 40 Landscaping" } } ``` ```json { "@context" : "https://schema.org", "@id" : "https://back40landscaping.ca/#back40landscaping", "@type" : "LocalBusiness", "address" : { "@type" : "PostalAddress", "addressCountry" : "CA", "addressLocality" : "Abbotsford", "addressRegion" : "BC", "postalCode" : "V4X 1Y5", "streetAddress" : "30353 Sunset Cres" }, "image" : "https://back40landscaping.ca/hubfs/Logo/test/back-40-landscaping-logo-white-transparent.webp", "logo" : "https://back40landscaping.ca/hubfs/Logo/test/back-40-landscaping-logo-white-transparent.webp", "name" : "Back 40 Landscaping", "openingHoursSpecification" : [ { "@type" : "OpeningHoursSpecification", "closes" : "16:30", "dayOfWeek" : [ "Monday" ], "opens" : "08:00" }, { "@type" : "OpeningHoursSpecification", "closes" : "16:30", "dayOfWeek" : [ "Tuesday", "Wednesday", "Thursday", "Friday" ], "opens" : "08:00" }, { "@type" : "OpeningHoursSpecification", "closes" : "12:00", "dayOfWeek" : "Saturday", "opens" : "09:00" } ], "sameAs" : [ "https://www.facebook.com/back40landscaping.ca/", "https://www.instagram.com/back40landscaping.ca/", "https://www.youtube.com/channel/UCPBamgRYCxNTbnbCN1ehbGA", "https://www.google.com/search?q=back+40+landscaping&oq=back+40+landsca&aqs=chrome.0.0i512j69i57j46i175i199i512j69i61l3.3447j0j7&sourceid=chrome&ie=UTF-8#lrd=0x5485cb6c3c1abc6f:0x7093e643eeb29c6c,1,,," ], "telephone" : "(778) 808-6961", "url" : "https://back40landscaping.ca/" } ``` ```json { "@context" : "https://schema.org", "areaServed" : [ { "@type" : "Place", "name" : "Chilliwack" }, { "@type" : "Place", "name" : "Abbotsford" }, { "@type" : "Place", "name" : "Mission" }, { "@type" : "Place", "name" : "Langley" }, { "@type" : "Place", "name" : "Burnaby" }, { "@type" : "Place", "name" : "Maple Ridge" }, { "@type" : "Place", "name" : "Port Coquitlam" }, { "@type" : "Place", "name" : "Surrey" }, { "@type" : "Place", "name" : "New West Minster" }, { "@type" : "Place", "name" : "Walnut Grove" }, { "@type" : "Place", "name" : "Crescent Beach" }, { "@type" : "Place", "name" : "Mt. Lehman Area (Abbotsford)" }, { "@type" : "Place", "name" : "Promontory (Chilliwack)" }, { "@type" : "Place", "name" : "Anmore (Port Moody)" } ] } ``` ```json { "@context" : "https://schema.org", "@type" : "Review", "author" : { "@type" : "Person", "name" : "Springman" }, "itemReviewed" : { "@id" : "https://back40landscaping.ca/#back40landscaping" }, "reviewBody" : "Sam and his Back 40 team were amazing to work with on our retaining wall project. Very professional and upfront from the moment he came by to look at our old failing wall, and worked around a few tricky spots and provided an amazing final product. We would use them again in a heartbeat and easily recommend them to anyone looking for quality and efficiency." } ```