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:
- Top Failure – the top collapses forward because the wall was too weak to retain the force behind it.
- Breach – the wall bursts in the center. This is usually caused by weak or improperly installed materials.
- 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:
- You push vinyl sheet pilings into the ground. Don’t hammer them.
- 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.
- Keep the sheets straight (vertically and inline) as you drive.
- You may find it easier and faster to drive two sheets side by side instead of strictly driving one at a time.
- Use properly treated wood for your wale and backboard and make sure they are solidly connected to the sheets and one another.
- Use galvanized or stainless steel hardware.
- Building a vinyl retaining wall is hard work and requires equipment. Expect it.
[youtube:http://youtube.com/watch?v=vcaPHq1T7S4]
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.
[youtube:http://www.youtube.com/watch?v=RefZ0caGE2E]
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.
Thank you for the great information! I’m a camp director for a summer camp and I am very interested in either the wood retaining wall with vertical boards, or the timber wall and I have two questions- We are trying to build an outdoor, amphitheater style chapel for our camp. This chapel will be constructed on a lakeside, and will consist of 3- 15foot X 16foot sections that will contain the seats or benches (2X10X16’s), which will be built on top of 6X6 landscape timbered boxes or terraces. Because our lakeside slope is too steep for walking up and down the aisles, we have determined that we will need a roughly 60 foot long retaining wall that will have to be 6 1/2 feet tall (and this wall will not come in contact with our lake). In your timber examples, what size timbers are common- 6X6’s? Or, when you describe timbers, are you referring to larger railroad ties?
One other question please- with one of these wooden walls, will the filter cloth be adequate for drainage? No need to intall some type of drains underneath the backfill. I hope not- if only the filter cloth is needed, then this would be fantastic news and not so complicated.
Thank you very much for your help
Casey
Casey,
I am glad Lumber Talk has helped you.
Q&A1. 6×6 timbers are probably ok for your wall IF you use a great tie-back system. The timbers are strong so I would not worry about them breaking (or “blowing out”) but a wall built with any size timbers might fall over. Tie back with tie rods or timbers turned into the earth (like in the side view drawing above).
Q&A2. It depends upon the type of soil behind your retaining wall. If the soil is very heavy with clay, which does not drain well, then you should give it every possible opportunity to drain, including using drains. If the soil is very granular, such as sand or gravel, then filter cloth alone is probably fine.
As always, please consult an engineer or builder who is familiar with the area.
Thank you for your questions.
Chris
Regarding the timber retaining wall and the tie-back timbers. In the front view picture the tie-back appears to extend out and flush, with the main timbers butting up to it on either side. In the top view picture the tie-back appears to butt up against the back of the horizontally running main timbers, which would seem right to me. Which is correct and is the tie-back secured to the main timber with spikes or rebar? I’m ready to go to work once I get cleared up on this.
Thanks so much for the instructions.
Dave
Hi Dave,
The tie-back timber should extend between the ends of the timbers in the wall and be flush with the front of the wall. This allows you to fully connect the tie-back timber (top, bottom, and sides) to the other timbers with spikes and re-bar if you are using re-bar, too.
Good luck on your project. Enjoy!
Chris
I was wondering if I used galvanized poles and set them in concrete, drill holes in the timbers and then anchor them together using 8″ long screws, would I still have to worry about blow out or tipping? Has anyone seen this type of retaining wall built?
John,
Overall, there is not information there to answer your questions. Please be more descriptive. What KIND of wall are you building? How deep are you setting your poles? How big are they? What are you supporting?
I would basically always suggest using a tie-back system.
Chris
Chris,
Your instructions for building a timber retaining wall seem pretty straight forward, but I would like to use some old railroad ties we just received for free. They are 6″ X 8″ and about 8 feet long. Would I need to do anything different or additional because I am using this material or could I follow the timber instructions?
Alyce
Hi Alyce,
The basic instructions are the same for most wood materials except that I am always weary of using old or used railroad ties. They are often rotten inside. Please test them before using them by sawing a few in half or hitting them pretty hard with a sledge hammer. If they seem solid enough to you, then go for it!
I don’t trust old rail road ties – they are old and are usually taken out of commission for good reason.
As always – all the best to you and ENJOY your project.
Chris
I have a couple questions first I need to know what to use in the anchoring system like a buried timber and cables or what, second what to use as the filter material and where would I get it any help would be appreciated
Hey Jeff,
For question about the anchoring system, please re-read the article above as I think that is covered at least once. If you have a more specific question let me know.
For the filter material, use “geotextile” – a thick black “filter cloth” material. American Pole and Timber can sell it to you – http://www.AmericanPoleAndTimber.com.
Thanks!
Chris
I am constructing a timber retaining wall using pressure treated 6×6 timbers. The wall will be 18 inches high on level ground 4 feet in front of an existing masonry retaining wall that is 27″ high. I am receiving conflicting advice on how deep I need to make the trench and bury the first course, and whether or not tie backs are appropriate. Any help is appreciated.
Mike
Mike,
It’s always tough to call these things without being there. I will always err on the side of strength. With that, bury the first row 1/2 or 3/4, drive re-bar vertically through all the timbers extending a foot into the ground, and use a tie-back system.
That is not advice, by the way. It’s just the approach I would take.
Chris
Chris,
In building a Timber retaining, wall how close together should the re-bar be placed if I only put rebar through the first 2-3 levels and then use galvanized spkes to conent the remaining levels. The approx length of wall is 3-35 ft and about 3.5 Ft high.
Also, my soil is all sand do i need to lay a layer of gravel under the first row of timbers?
Thanks
Dan,
That’s a good question but I wouldn’t touch most of it with a ten foot pole. There are too many variables to consider and I’d sure hate to guess wrong.
Sand should be fine as it settles evenly and allows water to drain well.
Thanks for writing – sorry I can’t do more.
Chris
Could 6×6 posts cemented 3 to 4 ft deep every 5ft be used instead of deadmen? I’m looking to build a wall 85ft long wall with an average 6ft height.
Hey Joe,
6×6 posts are certainly strong pieces of wood and occasionally used as deadmen when people have old ones laying around. Otherwise, they are simply too expensive for that use.
Are you burying them or building a fence behind your retaining wall?
Enjoy your project!
This is great information. Thank you.
I have a 3 foot high by 20 feet retaining wall, horizontal wood boards, and 4×4 posts spaced about 6-8 feet apart. We have a shed that’s about 2 feet from the wall. A couple of the posts are rotting from the top and one of the horizontal boards behind our shed is broke. What are your recommendations for replacing the posts and fixing this horizontal board? Thanks.
Hi David,
That’s a tough one and you WILL get wet and messy while repairing. That being said, I’ve seen people build onto and around by driving new posts adjacent to the existing broken posts, bolting or lag-screwing them to the existing posts, and putting the new horizontal boards on that.
The proper way (but your shed makes it tough) is to dig it out and rebuild that section. If the whole wall is 20′ you may as well rebuild the whole thing if you go to that much trouble, though.
Good luck!
Next time, use vinyl coated wood so your grandkids will have to deal with it. 🙂
I am considering building a wood retaining wall with vertical boards aprox. 4′ high using 6×6 pt posts. My question is how far apart should the posts be and are these set in just like a fence post with concrete or are they just packed in. Thanks
Rob,
The spacing of your posts depends upon the size of your horizontal boards AND the slope of the ground behind your wall (the load). You should consult an engineer or contractor experienced in your area.
The general rule for the depth of the posts is 1/2 in 1/2 out. So, if your wall has 4′ exposed you should drive the posts 4′ into the ground. You probably will not need concrete, especially if you use a good tie-back system.
Chris
Hey Rodger,
That sounds like a great project – boathouse and deck included. Very cool. New walls are built in front of existing walls all the time. I am not going to take a stab at the length of the tie-back timbers (for obvious liability reasons) and your best option there is to call a local construction professional or engineer.
It all sounds reasonable to me EXCEPT I am not so sure I agree with any ideas that the old wall is stable. If it was, it wouldn’t be leaning forward.
Enjoy the project, the end result, and life in general.
Chris
Hi great info, looking to build a 42′ long x 5′ high horizontal wall with the 6×6 timbers but have a few more questions.
1. For the “deadmans” how long should the extend from the back of the wall because I only have about 5′ of depth to work with. So can I do a 4′ deadman with a T design to add more strength.
2. Should I also do some vertical boards to help with support do to the size of the wall.
3. I want to cover the face with a stacked stone. Is this possible and if so what will I have to put on the face (cement board, roofing paper with chicken wire, ect.)
Thanks Stephen
Chris, great site, really informative and extremely helpful. I’m building a playland enclosure (4 walls in a rectangle full of mulch with a swingset on the mulch) using wood timbers laid horizontally and driving 1/2inch rebar to anchor to the ground and connect the timbers. The enclosure is 24ft by 28ft. The wall will be 2.5ft at it’s highest and 8inches at its lowest. Questions for you:
1. Do I need tie-backs that go into the mulch or does the rebar do the job? I was going to sink the rebar the same amount it sticks out of the ground.
2. Is the rebar enough to connect the timbers or should i drive 8inch nails too?
3. I was going to drive rebar in every 4ft, does that seem often enough?
4. Do you put anything over the rebar tip or just leave it exposed, but fully sunk in the wood.
5. I planned on using a 1/2 auger drill bit. Will that leave the 1/2 inch rebar snug enough in the wood?
Thanks for the insight.
Preston
I am attempting to build a 7′ retaining wall underneath my deck. The deck posts are in the mix, therefore my question is how far behind the posts should I place the wall? Should I put the wall on the inside of the posts? Seven feet tall is not too high is it?
Thanks,
John
Hey Stephen,
Sorry it took so long to reply. There’s a lot going on. It sounds like you have some real constraints to work with. You might want to build a “navy wall” which is basically a normal wall with pilings driving immediately in front of the wall (water side) for additional support. This is commonly done with taller walls but it might be a good solution to allow for shorter tie back rods.
As always, you should definitely consult an engineer before doing something like this and certainly take an engineers advice over mine.
Thanks for reading.
Chris
Hi Preston,
There’s a lot going on there and I hate answering questions like that too specifically. Here’s what I (that’s a big boooooold capital “I”) would do…
1. No tiebacks – it’s just mulch. I would use longer rebar – driven into the ground much farther, especially on the taller sides.
2. Depends on the size of the timbers. 4X4’s would get rebar only, 6×6 or larger would probably get some nails, too. (those dudes are heavy)
3. Every 4 feet seems fair enough but, again, I would drive it deeper into the ground – like 2X height of wall into the ground.
4. Fully (FULLY) sunk into the wood. We don’t want any accidents with the kiddos.
5. Hmm, you’ll have to test that one but you are right that it should be very snug. Remember that treated wood will shrink when it dries.
I hope this got to you before your project. Otherwise, I hope it helps someone else. Great questions!
Chris
p.s., all that stuff is just what I would do. 🙂
John,
I don’t get it. Give a little more description and I will be more than happy to give it a shot.
Thanks!
Hi,
I’m building a 4′ retaining wall that is 70′ long. There is a creek about 40 yards away but the water will not be reaching the retaining wall. Im in northeast FL what type of drainage if any you would recommend?
I will be using 8” butt x 8′ for the piling. I’m spreading them apart every 6′. The whalers will be 2”x8”x12′ that will be double stacked onto the pilings. What is the proper size screw I will need to attach the whalers to the pilings?
I will also be using 2”x8”x10′ cutting them in 1/2 for the wall. What is the proper size screw to attach the wall to the whalers.
Thanks!!
I am looking at building a horizontal retaining wall that will probably be about 2 to 2.5 feet tall at highest point and 20 foot long. I am |_| shaping this on uneven ground to level out for a 12×16 gardern shed to sit on. Question is what size wood should i use 4×4, 4×6, or 6×6. I was thinking of 4×6 but just curious. I will be back filling with rock to level out for the shed. And also would i be better off putting a hard lime rock in that will set up or just back fill with pebbles for water drainage.
Thanks
Hi! Hoping for some help today!
We are building a 2 ft retaining wall at the front of our property. We plan to use square steel tubes as fence posts and 2 courses of 2×12″ wood placed horizontally. We are also planning to build a fence right on top of this wall by using 8′ steel tubes to anchor both the retaining wall and the fence above it. We think to sink them 3′ down, 2′ retaining wall and then 3′ fence.
Our problem is- what do we do about the sides of the wall? The 2 sides of the wall- one borders our neighbors property and the other borders our driveway. Do we build the sides of the retaining wall too? (like a 3 side huge planter box?!) What sort of anchors do we use if we have to turn the corner of the front retaining wall with the 2×12′ boards?
I have a 6×6 x16ft pressure treated post which has a slight twist from end to end – how can I remove the twist ?
– if I puton flat surface & put heavy weights on each end, and constantly soak the whole unit , then let it dry in summer heat over 2-3 week – (soak & dry, soak & dry, 3 -4 times) will this be the right action?
Hey Brian,
That should do it – soak, weigh it down, soak, weight it down. That is a strong piece of wood. It will take some SERIOUS weight – like a car on each end. No kidding.
Dawn,
sorry for the slow response. I have trouble getting to this sometimes. Ask your neighbors. Maybe they want to build onto yours. Otherwise, it is very common to build “wing walls”, which are just short walls (3 to 6 feet) that extend back and protect from erosion and such.
Enjoy it, either way.
Chris
Hey Chuck,
Cool project. If it were mine, I would always opt for bigger timbers. Dirt is heavy. I would use 6×6’s or 4×6’s laid flat and backfill with a granular dirt (pebbles, sand, dirt). Have fun building the shed. Whistling helps.
Ron,
Unfortunately, I totally missed this one so it’s probably too late to help. Either way, if by “drainage” you mean backfill then you should probably use something granular like sand or dirt with pebbles so the water will drain away instead of holding pressure on the wall.
You’ll need lag screws for the whalers – min 5/16″. I am known for “overbuilding” (but my structures don’t break) so I would use 3/8″ or even 1/2″. For an extra dimes per piece you will sleep easier for another 10 years. Tip. You will often save money (a lot) on hardware by buying it from a local small business lumber dealer instead of through a hardware store or big box like Home Depot, etc. You might get better/friendlier service, too.
For the boards/sheets/centermatch use big stainless screws. You’l know ’em when you see ’em.
Tip for the boards – cut the 10 footers in half at about a 35 degree angle. When you drive the boards into the dirt, the angle will automatically force them against the adjacent board (the last board you installed).
Chris
Chris;
I want to build a soundproofing wall with timbers. This would not be a retaining wall, but a free-standing wall. I was thinking of making it 12 inches thick, using two walls of 6 by 6 eight foot timbers and attaching them together somehow. I would like to make it six feet high. Any suggestions, recommendations, or alternative approaches? The wall will be forty feet long.
Steve
Addendum-
A lot of people say to put #57 gravel under the base timbers, but you don’t. Why not? Also, my project is designed to keep out road noise, and the road is sixty feet away, and the road level is fifteen feet lower than the base of the wall, and partially blocked by an embankment.
Hi Bob,
That sounds like a great plan. I would use .60 treated timbers, though, to ensure they last a really long time. Also, some people use a ‘3X the height of the wall’ rule-of-thumb for the tie back rods, which would put yours at more like 9 feet long but you are probably ok with 5′.
Your plan is great overall.
Hey Steve,
You know what? I don’t know much about sound proofing so you got me there. Putting the posts two feet in the ground is right on the edge of adequate, though. You might consider putting more in the ground (via longer posts or a shorter wall).
I might recommend gravel if you are in a place with very clay soil and slow drainage. Otherwise, the lack of oxygen underground (along with well-treated timbers) is the best protection.
Sorry, Frank. I can’t say I know anyone up there. Anyone? (spam is filtered but I don’t mind sending Frank an email with legit info).
I don’t know what you mean by “deal with” and “overhanging away from wall.” I am happy to help if you help me understand, though.
Chris,
I will be building a 30’x5′ retaining wall on my lake front property. Your comments in this section are noted and appreciated. The lake where the work is to be done is down and I can work in the area and not deal with water in setting the pilings. I have 3 questions.
1.I will be using 6″x12′ treated round posts. Can I auger down 5′ to set the post and fill with concrete or should I backfill with dirt (mostly silt & clay)? I was told that concreting the post under the lakebed could cause the post to rot faster.
2. If I don’t have room to use a deadman, can I set the posts every 2-3 feet for support versus every 4-6 feet? or should I excavate back further to install the deadman? I have about a 10 degree slope to the edge.
3. Can I backfill behind the wall with the clay/silt that was pulled from the lakebed or should I use gravel?
Mark
Chris,
we just took out a round pool out of our back yard, an are transforming it into a fire sunken in fire pit. i have a bunch of 4×4 and we are making it shaped like half of a stop sign. and we want to put in three steps. how should we go about starting and what materials do we need other than our 4×4? thank you