Skip to main content

As promised, this is the second of five parts on wall construction. In this feature, I'll provide you the information to build a pressure-treated wall. I have not included railroad tie walls in the discussion because, here in the Southeast summer's heat, the preservative tends to liquify and eventually get into the groundwater (big no-no) and the kids will drag the tar into the house, making mama very unhappy (equally big no-no). From a construction aspect, the ties may have big spikes in them, requiring arduous removal, and the tar will eat up a saw blade very quickly. That said, if you have an available supply of RR ties and you can put up with the noted downsides, have at it.

Here are some varied uses for timber walls -- have a look and then we'll get started; note particularly the manner of staggered joints and the tiebacks or "deadmen."

Building timber walls(click thumbnails to view gallery)

Pressure-treated timber wallPressure-treated timber wallPressure-treated timber wallPressure-treated timber wallPressure-treated timber wall


First off -- safety: you will need safety glasses, dust mask, gloves, hearing protection, protective chaps ( if you use a chainsaw); all the items are self-explanatory or will be, when you get started on the project.

For our purpose, walls are based on a maximum height of 4'; those exceeding that height generally need a permit (check with your local building code authorities) and a good idea would to get an engineer to spec your project, or get a licensed and experienced pro to do the job. You can, of course, build multiple walls 4' tall; they have some setback guidelines you should observe, but this is an option to increase the height of the structure. Walls less than 2' in height generally don't need gravel backfill or sockpipe drainage provisions; there is not usually sufficient hydrostatic pressure to bother with, given the gaps in the wall timbers.

Materials:

  • 6" x 6" ground contact pressure-treated timbers; they come in various lengths, but the easiest to handle is the 8' size; you'll need one 8' timber for each 4 square feet of wall + one timber for each 3 1/2 lineal feet of wall, for the "deadman" or tieback system. Get them delivered; you don't want to make multiple trips with these guys, sticking out of the top of your convertible.
  • 1/2" or 3/4" rebar to pin the first lift of timbers in the trench; 4 pieces of rebar for each base timber. Get them delivered with the timbers.
  • 10" x 3/8" galvanized spikes -- you'll need about 4 per timber; buy them by the box ( they're cheaper that way) and have them delivered.
  • gravel for drainage backfill, if the wall height exceeds 2' -- get the stuff that's about the size of your thumb (#57 stone); it goes about 6" to the rear of your wall and about 3/4 of the height. Get about 25# for each square foot of wall; get it delivered so you don't have to haul it in the aforementioned convertible.
  • soil backfill -- since most walls are dug into a hill, you should have sufficient excavated soil for backfill behind the gravel; it's when you get into walls taller than 4' that you need extra; that calculation depends on the design of the wall (see above for the need for an experienced professional.)
  • sock pipe, if the wall height exceeds 2' -- one foot for each lineal foot of wall.; used to carry water away from behind the wall. It's slotted pipe with a permeable sock on it to keep the pipe from clogging and goes behind the second course of timbers, with the drainage to the downhill end of the wall. (This will fit in your convertible.)
  • landscape fabric -- placed against the back of the wall; allows water through, but not soil. Get one square foot for each square foot of wall. (As will this,)

Time: if this is your first wall, a 4' tall x 24' long wall will take you about 2 days to build, assuming you have all the materials on hand. Needless to say, the more help you have, the faster it will go; sounds like payback time for the help you've given your kids or friends?

Tools:

  • An electric drill with 1/2' or 3/4" bits for drilling the rebar holes; don't use a battery drill -- you won't be able to keep up with the battery drain.
  • tape measure and carpenters pencil.
  • shovels, rakes, and perhaps a wheelbarrow.
  • a hand tamp for compacting the backfill behind the wall.
  • small and large sledgehammers for driving the rebar and spikes (pre-drill the whole timber for the rebar and half the thickness of the timber for the spikes.)
  • a 10" carpenter's chop saw (may be rented for about $35 a day), circular saw, chainsaw (optional-- they don't provide nice, clean cuts like a chop saw does).
  • large carpenters square.
  • a level at least 4' in length.
  • a torpedo level to ensure that your timbers are not leaning forward or backward; the level is 8-9" long and used in confined spaces.

The process, again assuming a 4' wall:

  • excavate a trench as long as your wall, about 8" wide and deep; you want to bury the first course of timbers completely. Lay in your timbers, end to end, and level -- use tamped, excavated soil as a base and your 4' level to ensure the wall is level side to side; use your torpedo level to ensure the timbers are level front to back. The first course is the most time consuming to install; take your time to ensure it is level side to side and front to back or you'll not have a good looking, sturdy wall. Stick the timbers to the trench with your rebar, spaced 4 pieces to the timber, through your drilled holes.
  • fill the trench with excavated soil, tamping the soil around the timbers.
  • add the next course of timbers, staggering the joints and setting each subsequent lift approximately 3/4" to the rear -- this is called "batter" or setback and provides strength to the wall by "leaning" it into the slope. (Now is a good time to review the photo gallery above to note the staggering of the joints and to prepare for the next step, installing the deadmen). Use your levels to ensure side to side, and front to rear, level.
  • "deadmen" or tiebacks are those timbers installed perpendicular to the wall which provide strength. The face of the deadman is flush with, or slightly protruding from, the face of the wall, and extends to the rear in a length corresponding to the height of the wall (e.g. if the wall will be 4' tall, the deadmen are approximately 4' long). The tiebacks are nailed together to form a box -- see the excellent example here. Spike them together on at least two faces.. They should be emplaced every 8' along the wall and every third lift high, up to the last two courses -- no deadmen here or they will interfere with your sod or plantings atop the wall.
  • gravel backfill, about 6" behind the wall -- use it starting at the second course and continuing as you increase the wall's height, stopping two courses from the top so as not to interfere with sod or plantings.
  • as you backfill with the gravel, place the landscape fabric against the rear of the wall, holding it in place with the rock.
  • soil backfill goes between the gravel and the slope of the native soil and fills the "box" you constructed with the deadmen. Tamp the soil thoroughly, in approximately one foot lifts. It's a little cumbersome, working the soil in and around the timbers, but the more you tamp, the stronger the wall. You sure don't want this baby to fall down, after all the work you've put into it, not to mention the embarrassment factor.
  • fill behind the top two courses with good native soil, or that plus some soil amendments and you are ready for sod or plantings.

A final note; my experience is that timber walls, in the shade, will last about 18-20 years; in the sun, about 14-16 years. That's the downside; as with just about everything in life, however, proper maintenance will increase the longevity of a wall (or a relationship with a girlfriend, boyfriend, husband or wife -- not that a reminder of the upcoming Valentine's Day would be necessary); when you note the wall is getting a little dull in appearance, pressure-wash it and give it a shot of wood sealer and it will last through a bunch of Valentine's Days.

There you go; it's all yours now -- have fun.



  • Willy

    How do you feel about pressure treated lumber as opposed to railroad ties? Don't RR ties have more "character"? Will they last as long as pressure-treated lumber?

    Reply
  • James Colson

    The short answer is no. The reason why is because the railroad ties that are used in constructing a retaining wall are not NEW. They have been removed and sorted by the track company. New crossties would outlast new pressure treated timbers, but they would be considerably more expensive.
    So when choosing between crossties and timber, go with timber. As a consumer you should be aware of what grade timber. For retaining walls you want Ground Contact treated timber rated as # 3's. There have been cases where companies have installed timber that was not rated for ground contact and three years later they are replacing the wall.
    Also you should be aware of the best alternative to both which would be concrete modular block. This type of retaining wall when properly installed is designed to last better than 50 years. It is more expensive but will not need to be replaced further down the line.

    To get more information feel free to contact me at james@rwallsinc.com or visit http://www.rwallsinc.com


  • bill.volk

    Willy--a good question. RR ties will likely last as long as timbers, but I have little experience with them, given their construction downsides; I don't think the character factor is a plus. I forgot to mention, in my feature, that chipmunks and yellow jackets (yikes!) love to take up residence in RR ties, but not timbers.
    Thanks, Bill

    Reply
  • Rube

    When using 3 high 6 x 6"s is a deadman needed. I'll be driving in the first course with 3' rebar and spiking the nest two into that

    Reply
  • Bill Volk

    No need in this case; the rebar in the base timber and spiking them all together should do just fine. I would suggest that you still emplace the first timber a bit below ground level, to prevent kickout, and be sure to put some setback into the wall. Thanks for the question.
    Bill


  • Ken

    The ground is sloped where I want to put the retaining wall. The top of the wall will remain level. Can I just step up the next ground timber as long as the each one is partially buried? How much overlap should I use (side to side)?

    Thanks, Ken

    Reply
  • Tom

    what would be different if you wanted to utilze this as a driveway extention no higher than 2 foot filling with gravel

    Reply
  • Bill Volk

    Tom -- thanks for the question. I would be concerned that the weight of the vehicle would cause it to sink into the gravel. I wouldn't do it unless you thoroughly compacted the gravel and topped with at least 6" of concrete + rebar. Also, you want to make sure that the vehicle doesn't run off the end!!
    Bill


  • Eric

    I'm looking to make a raised paver patio in SE Wisconsin. First, I would think it wouldn't be too hard to make a 3 course (or so) high timber wall, fill it with gravel and sand and then put pavers on the top. Does that sound like it would work, or should I go with stone. If it would work, would I need to worry about the winters here heaving stuff around? I could bury the first course and use rebar down into the yard, but I think our frostline usually needs a 48" deep hold dug if you were going to bury posts or whatnot for a deck.

    Reply
  • Bill Volk

    Eric--thanks for the question. That's a typical application here in Georgia, although our frost line is only about 1". I'd recommend that you use at least 6' of deadmen, tamp the gravel thoroughly, and dig in the first lift of timbers. Certainly the frost heave is going to be a major concern, but if you use enough rebar (perhaps 6' length) I think it's an acceptable risk.
    Bill


  • Eric

    Sounds good! Forgive the newbie question. I'm assuming that a "deadman" is a timber lying perpendicular to the wall and in my case would be under the patio?

    Reply
  • Bill Volk

    Eric--sorry; "deadmen" is a local term. You're probably more familiar with "tieback", but yes, it is perpendicular to the long axis of the wall and goes under the gravel.
    Good luck.
    Bill


  • Ron

    Couple of questions.

    1. You mention using 6" x 6" timbers, but the timbers in the gallery look larger. If so, can you tell me the approximate size?

    2. Isn't better to place the landscape filter between the gravel backfill and the soil instead of directly on the timber wall to keep the soil out of the gravel?

    3. I'm building a level area bounded on three sides by a timber wall. Drainage will be required. What's the easiest method to get the drainage pipe exit to the outside of the wall?

    Reply
  • Nadeem

    I I have a 4.5' exposed wall with 2 course below the grade. I am an
    Eengineer & needs to design this wall. Is there any good design example available for this type of wall as I have experience in the design of concrete & MSE walls.
    TThanks for the help
    nnadeem

    Reply
  • Bill Volk

    Thanks, Nadeem, for the question. Do I understand that you need some help with the design for a pressure treated wall? If so, I think that the article will help quite a bit. If not, please let me know your specific questions and I will try to help.
    Bill


  • Nadeem

    TThanks Bill for the help.
    II I need help in term of submitting stability analysis. Normally for a
    c cantilever retaining wall, pressure diagram will be triangular. What
    s shape will the pressure diagram will be. Also, how to check the stability of the individual pieces. I mean to say what is the allowable
    foforce for these 1/2" railroad spikes. If there are sample calculation for this type of wall, please let me know.
    ththanks


    \

    ii


    Reply
  • Bill Volk

    Nadeem - a pressure treated timber wall cannot be cantilevered, so I'm not certain I understand your question. As for a pressure diagram, you'd have to have a registered engineer do the calculations based on the design. The same goes for the lateral force on the spikes. Has this been helpful?
    Bill

    Reply
  • Dennis

    Two Questions:
    1. I've been told not to use rebar with the new pressure treatment. It will corrode it away quickly. Do you agree?
    2. I will be a long (100ft) but relatively low (2 1/2ft) high. Can I use
    4 x 4 instead of 6 x 6 to save cost?

    Reply
  • Bill Volk

    Dennis -- thanks for the question.
    Rebar will, indeed, corrode in time, but it will be a very long time. No concrete office building, highway, or big wall (concrete or wood) is professionally built without rebar, so don't give it a worrisome thought.
    As for the 4 x 4's: they are structurally less stable than 6 x 6's and, I suspect, if you look at comparable square foot costs, the bigger timbers are about the same price. I would stick with them.
    Bill

    Reply
  • Scott B

    I want to replace my pressure treated wall with stone. The wall is only 3 years old and I have a friend who would like the timber. How to I remove the spikes (rebar) from the pressure treated wood without damaging the pressure treated wood?

    Reply
  • 22 Comments / 2 Pages

Add Your Comments

  • New Users
  • Returning

If you are posting a comment for the first time, please enter your name and email address in the fields above. Your name will be displayed with your comment. Your email address will never be displayed.

Add Your Comment

Please keep your comments relevant to this blog entry. Email addresses are never displayed, but they are required to confirm your comments.

When you enter your name and email address, you'll be sent a link to confirm your comment, and a password. To leave another comment, just use that password.

To create a live link, simply type the URL (including http://) or email address and we will make it a live link for you. You can put up to 3 URLs in your comments. Line breaks and paragraphs are automatically converted — no need to use <p> or <br /> tags.

Advertisement

Follow Us

  • No features currently available.

  • More Hot Topics The Daily Fix  •  DIY Warrior  •  Home Ec  •  Handmade
    DIY Disaster Doctor  •  In the Workshop  •  Product Picks

    Home Improvement Videos