How to Build a Retaining Wall

When asked how to build a retaining wall, my response is almost always, “What kind?” This article covers the basics of how to build various kinds of retaining walls, including wood retaining walls, timber retaining walls, block retaining walls, and even vinyl sheet piling retaining walls. I will go over each wall in more details in following articles. If you want to know how to build another kind of retaining wall after you have read everything here along with the materials I have linked to, leave a comment and I will do my best to respond.

Basics of Retaining Wall Design
Remember that the forces on your retaining wall change with the weather. If the ground behind your retaining wall become saturated with water from rains or watering it will become heavier and put more force on your wall. The design and materials you choose for your retaining wall need to take into account what it will need to support during its darkest moments. If you have any doubts about your materials choice or retaining wall design, please call a civil engineer or professional contractor and spend a few dollars on a professional retaining wall design and/or installation.

Why a Retaining Wall Fails
Retaining walls typically fail in one of three ways:

1. Top Failure – the top collapses forward because the wall was too weak to retain the force behind it.
2. Breach – the wall bursts in the center. This is usually caused by weak or improperly installed materials.
3. Toe failure – the bottom of the wall comes up. This is usually caused because the retaining wall was not planted or supported deeply enough in front.

Each of these causes of failure can be avoided with the proper design, proper materials, and proper installation for your project. Please consult a professional before designing and building your retaining wall and please understand that this article should be used as a guideline only.

How to Build a Wood Retaining Wall

There are really two wood retaining wall designs. The main difference between the two designs is that in one of the designs the retaining boards are horizontal and in the other they are vertical. I personally think using the retaining boards vertically will give you a stronger wall because of the specifics of that particular design. Using the boards horizontally makes building the retaining wall a little easier, though, and still gives you a great wall that will last a long time.

Building a Wood Retaining Wall with Vertical Boards
This is retaining wall design commonly used to build wood bulkheads along shorelines. It is an effective design and the basic rules of it are pretty standard. The drawing is pretty self-explanatory but here are some more guidelines (PLEASE NOTE – the drawings leave out the tie back rods that I strongly advise you use. See the design for the vinyl retaining wall as they use the same tieback systems):

• The posts go about 50% into the ground (e.g., The posts of a 3′ tall wall will be 3′ IN and 3′ OUT)
• The retaining boards should go at least 1′ into the ground (part of the reason this wall is strong than using the boards horizontally)
• The filter cloth should be longer than the retaining boards and roll back away from the wall
• Use granular material (sand or small pebbles) to fill in behind the wall and allow water to drain
• Use at least two back boards but do not be afraid to use three
• For a stronger wall use “center match” or “sloppy tongue and groove” boards for the retainer boards
• You can use round posts or square posts
• Leave a comment if you have any other questions
• Use tieback rods and buried “deadmen” or other anchors for extra wall support to prevent top failure
• The tie rods should start at the front of the posts and extended through them and behind the wall where they bolt to the deadmen.

Building a Wood Retaining Wall with Horizontal Boards

This is probably the most common type of wood retaining wall built around gardens. Unless you are using really heavy materials or a professional retaining wall design, do not use this design to build a wall that is any more than 16″ or two feet tall. It is a simple design meant for small loads such as garden beds. For the moment, buildeazy has the best plans for building this kind of wood retaining wall so I will simply let you read their how to article and get on to explaining how to build other kinds of retaining walls.

How to Build a Timber Retaining Wall

Building a timber retaining wall is conceptually easy and physically back-breaking. If you use properly treated timbers and build the wall properly a timber retaining wall might last 30 years. Timber retaining walls are simple to understand, simple to design, and simple to layout. Using a backhoe or tractor to manipulate the timbers will make building one easy as well.

To build a timber retaining wall, begin by digging a trench along the line of where your wall will be. The trench should be approximately the depth and width of the timbers you will be using to build the wall. If you need space to work on the back side of the wall, dig that space out before you begin building the wall. Use a line level to level the ground where the timbers will lay. Place the first row of timbers flat in the trench. After your first row of timbers is laid along the ground begin stacking your second row of timbers and make sure to stagger the ends of the timbers to ensure a strong wall. Attach each layer of timbers to the layer below it with spikes (8 inch long 60D nails). Timber retaining walls are built straight up – not slanted like stone walls – so keep your timbers plumb as you stack them.

Timber Tie-Backs
If your wall will be higher than about 18 inches use tie-back timbers every eight or ten feet on various levels to hold your wall upright and make sure it will not fall forward due to the constant pressure exerted upon it from behind (top failure). To add a tie-back timber, simply lay one timber perpendicular to the other timbers but with its length extending into the area that will be back filled. When the area is back filled this timber will act as an anchor to hold the wall in place and ensurer your timber retaining wall can withstand time and rough conditions.

Timbers United into One Structure
One aspect of my retaining wall design which is a little different from others you may see is that I prefer to unite the entire timber retaining wall structure with re-bar driven vertically through all the timbers and into the ground via a hole that is drilled through all the retaining wall timbers after they are completely stacked. The re-bar should fit tightly into the drilled hole. This step might be an overkill but I like strong stuff that lasts a long time. An alternative but similar method is to drive re-bar through the bottom two or three layers when the wall is about half-built and then connect the bottom timbers to the top layers once the top layers are added (see pictures).

Use Properly Treated Quality Timbers
Some books and sites will recommend that you use “garden timbers” (those cheap ones with two round sides and two flat edges) to build a retaining wall but I strongly advise against that practice because “garden timbers” are typically made from the cheapest pieces of wood leftover from the production of other lumber or plywood and contain mostly heartwood which does not accept pressure treatments. They will probably be heavily rotted within a few years and will eventually fail. Building a timber retaining wall is hard work so use timbers that will last. You might even consider using timbers with a vinyl or polymer coating. American Pole and Timber is a reputable company that ships quality timbers nationwide and offers a few types of vinyl coatings that can make wood last virtually forever.

How to Build a Vinyl Retaining Wall

Building a vinyl retaining wall is basically exactly like building a vinyl bulkhead and since I have made a sketchast about that before, I am using it here (below). The main things to remember about building a vinyl retaining wall are:

1. You push vinyl sheet pilings into the ground. Don’t hammer them.
2. Lead with the male edge of the sheets because the female side gets clogged with mud and makes it almost impossible to add the next sheet.
3. Keep the sheets straight (vertically and inline) as you drive.
4. You may find it easier and faster to drive two sheets side by side instead of strictly driving one at a time.
5. Use properly treated wood for your wale and backboard and make sure they are solidly connected to the sheets and one another.
6. Use galvanized or stainless steel hardware.
7. Building a vinyl retaining wall is hard work and requires equipment. Expect it.

How to Build a Block Retaining Wall

Block retaining walls are built very much like the others and some people consider them the easiest type of wall to build. They also look very nice and allow you to easily build a wall with curves. The process of building a block retaining wall is fairly slow and painstaking because you are building with such small pieces but the end result is probably worth it. There are a million great tutorials already existing about how to build block retaining walls so for now I am going to point you to them and get on with other projects.

This video from Alan Block is far-and-away the best about how to plan a block retaining wall. I am not endorsing their products (at least not intentionally) but this is a really great video.

Other great tutorials for how to build block retaining walls can be found at PaverSearch, this student’s page, DoItYourSelf, and Lowe’s.

There are the basics of how to build retaining walls – five kinds of retaining walls, in fact. If you have any questions or want to know about another kind of retaining wall, leave a comment below. I will respond as quickly as I can. Thanks.

Construction Span Tables

I often get asked by engineers, architects, and designers (and farmers) about the span tables for dimensional lumber. So, I have compiled a list of many places with various span tables for your reading enjoyment and project fulfillment. The idea here is to create a one-stop shop for span tables so let me know if I am missing something.

Roof Truss Span Tables: This is a great find for roof truss span tables. It is easy to use and breaks down the span tables by truss type, pitch, and length. Here’s a list of roof truss manufacturers, too.

Maximum Span Tables for Joists & Rafters: The MSR Lumber Producers Council created and published these span tables floor joists, ceiling joists, and roof rafters. The pdf is 12 pages long and the span tables start on page 3.

Span Tables for Structural-Use Panels: Free pdf download from the APA Engineered Wood Association for Structural-Use Panel Span Tables.

Floor Joist Span Tables: Southernpine.com probably has the best publications – like this one showing floor joist span tables.

Residential Steel Beam & Column Span Tables: This is a pretty specific span table (warning: 29 page pdf) developed by the American Iron & Steel Institute. The span tables start appearing on page 12. If you are having trouble sleeping, start at the beginning. Otherwise, stick to the span tables.

Lumber Span Tables: This is a span table for U.S. Spans for Canadian Species from the Strober Organization, Inc. a supplier for contractors in the eastern U.S.

Header and Beam Span Tables: These span tables are a great find if you are trying to build with beams and/or engineered lumber. The pdf is free from The Southern Pine Council.

Deck Joist Span Tables: Their is a good span table tool in here for deck joists but I cannot link directly to it so go here and click on “Joist Calculator” about halfway down the page. You might have to sign up/in.

Span Table Pocket Card: This is like a cheat sheet from The Souther Pine Council. Every wood professional should have a copy of this around somewhere. The pdf is free or you can order the real thing (laminated) for $0.50 each.

Beam Span Tables: The American Institute of Timber Construction has a nice list of tools and span tables for timber construction.

Bridge Span Tables: This is just interesting and offers no actual value. It is a chart of the longest bridge spans around the world. By “span” they are referring to the distance between the two farthest-apart supports on the bridge (the longest spans). The lengths, which are in meters, are not referring to the total lengths of the bridges.

Tell me what I missed. I know there are a million other span tables out there and I would like to list them here. If you know of something, add it yourself as a comment and I will add it to the list.